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The Professional Barista’s Handbook

The

Professional

Barista’s

Handbook

An Expert’s Guide to Preparing

Espresso, Coffee, and Tea

Scott Rao

The author has taken care in preparation of this book but assumes no responsibility for errors

or inaccuracies.

Copyright 2008 by Scott Rao

All rights reserved. No part of this book may be used or reproduced in any manner whatsoever

without written permission, except in the case of brief quotations embodied in critical

articles or reviews.

Published 2008

Printed by [xxx] in the United States of America

ISBN 978-1-60530-098-6

Text and photographs copyright 2008 by Scott Rao

Photography by Alex Dubois

Email: [email protected]

Book design by Rebecca S. Neimark, Twenty-Six Letters

Please visit www.theprofessionalbaristashandbook.com for information about purchasing

this book.

This book is dedicated to James,

who generously gave me my first roasting lesson

and whose coffee set the bar impossibly high.

First and foremost I would like to thank Jean Zimmer for your knowledge, guidance,

and friendship. This book could not have been a reality without your encouragement

and help. To Alex Dubois, I am grateful for your time, energy, and patience

during our photo sessions. To Andy Schecter, Jon Lewis, James Marcotte, and Tony

Dreyfuss, thank you for your insightful and expert feedback.

Introduction x1

1. Getting Started 1

2. Espresso 3

Espresso Percolation: a Primer

Grinding for Espresso

Dosing and Distribution

Grooming

Tamping

Water Temperature

Putting It All Together

Preinjusion

Contents

Espresso-Making Techniques in Italy Versus America

Pressure Interruptions During Espresso Brewing

3. The Science and Theory of Percolation and Extraction 35

Percolation Dynamics

Fines

Basket Shape and Extraction

Espresso Brewing Ratios and Standards

4. Milk 45

Milk Steaming

Milk Pouring

5. Barista Systems 61

Efficiency Enhancement Tools

Work.flow

6. Drip Coffee 67

Freshness

Drip Brewing Standards

Grinding

Temperature

Turbulence

Optimizing Different Batch Sizes

Coffee Brewing Chart

Setting Up the Filter

Stirring: the Key to Making the Best Drip Coffee

Programmable Brewer Settings

How to Hold Brewed Coffee

Brewing Drip Coffee to Order

Coffee Filter Types

Freezing Coffee Beans

7. French Press Coffee 79

How to Make Great French Press Coffee

8. Water 81

Water Chemistry 101

Brewing Water Standards

Water Treatment

Descaling

9. Tea 87

Basic Tea-Making Guidelines

Preparation by Tea Type

Appendix 91

References 93

Glossary 95

Index 98

Introdt1ction

When I began in the coffee business fourteen years ago, I read every book I could

find about coffee. After reading all of those books, however, I felt as if I hadn’t

learned much about how to make great coffee. My coffee library was chock-full of

colorful descriptions of brewing styles, growing regions, and recipes, with a few

almost-unreadable scientific books mixed in. I would have traded in all of those

books for one serious, practical book with relevant information about making great

coffee in a cafe.

Fourteen years later, I still haven’t found that book. I know many other professionals

as well as some obsessive nonprofessionals would like to find that same

book I’ve been looking for. This book is my attempt to give it to them.

Chapter 1

Getting Started

Equipment

There will be many opportunities throughout this book to test and practice different

methods of making coffee. To get the most out of the recommended techniques

it is useful to have the following equipment on hand.

• A commercial or prosumer (professional-quality machine designed for serious

consumers) espresso machine.

• A commercial or prosumer espresso grinder.

• A tamper sized properly to form a good seal with your portafilter baskets.

• A bottomless or naked portafilter.

• Nonessential, but helpful, are a Scace Thermofilter™, a timer, a thermometer,

and a gram scale.

Standards

A “shot” of espresso can mean something different from barista to barista and

country to country. For the purposes of this book a shot of espresso will be broadly

defined as having the following parameters.*

ESPRESSO

BREWING RATIO EXTRACTION PRESSURE EXTRACTION TIME TEMPERATURE

6.5-20 g grounds to

.-1ó oz (21-42ml) water 8-9 bar 20-35 seconds 185°F-204°F

These standards are not recommendations; they are simply meant to reflect common, current

practices. Please refer to the appendix for a more comprehensive list of coffee, tea, espresso,

and water quality standards.

Some Fundamental Terms

Extraction is the removal of mass from the grounds. Extracted substances are either

soluble or insoluble.

* It is traditional to measure shot size volumetrically, but it is far more useful to measure shots by

mass. Volumetric measurements can be misleading due to variations in crema quantity; different

amounts of crema can distort one’s perception of how much liquid espresso is in a shot. (See

“Espresso Brewing Ratios and Standards” in Chapter 3.)

In drip coffee and espresso, “solubles” are solids and gases dissolved in the

brewing liquid. Soluble solids contribute to taste and b,·ew stl’ength while soluble

gases, or volatile aromatics, contribute to aroma.””

In drip coffee, “insolubles” are solids and oils held in suspension. Insoluble solids

are made up primarily oflarge protein molecules and fragments of coffee fiber.””

Insoluble solids and oils combine to form b,-ew colloids. These contribute to aroma,

body, and taste and alter.flauo,- by trapping and later releasing soluble solids and

gases”” and by buffering acidity.

In espresso, insolubles are held in either a suspension or an emulsion. The suspended

solids are primarily coffee bean cell wall fragments that contribute to body

but not flavor. The emulsion is a dispersion of tiny oil droplets surrounded by liquid;

these oils contribute to aroma, body, and taste and also act to decrease the

perception of bitterness of an espresso·* by coating the tongue. 9

EXTRACTION

SOLUBLES

SOLIDS GASES

I

TASTE AROMA

INSOLUBLES

SOLIDS OILS

BREW COLLOIDS

BODY, TASTE,

AND AROMA

•-An espresso tastes more bitter when made into an Arnericano because the addition of hot water

dilutes the oil content, which prevents the oils from completely coating the• tongue.

2 Ge/tiny Sturted

Chapter 2

Espresso

Espresso is a small, made to order, concentrated coffee consisting of liquid topped

by foam, or crema. The liquid and crema are each multiphasic systems consisting

of an emulsion, a suspension, and a solution. 9

Crema is composed primarily of CO, and water vapor bubbles wrapped in liquid

films made up of an aqueous solution of swfactants. 3″ Crema also contains suspended

coffee bean cell wall fragments, or.fines (responsible for “tiger striping,” or

mottling), and emulsified oils containing aromatics.:10

The liquid phase of an espresso consists of dissolved solids, emulsified oils, suspended

fines, and an effervescence of gas bubbles.”

Espresso Percolation: a Primer

What follows is a general overview of espresso percolation. This section is not intended

to be comprehensive, but rather to introduce the fundamentals.

3

The Basics

Espresso is produced by the percolation of pressurized hot water through a tightly

packed bed of finely ground coffee. The water erodes solids and oils from the surfaces

of the coffee particles as it flows through the coffee bed and deposits the solids

and oils in the cup.

The flow rate of the water through the grounds is determined primarily by the

amount of pressure applied by the machine, the mass of the grounds, and the fineness

of the grind. Higher pressure, up to a point, increases the flow rate; beyond

that pressure, flow rate decreases. A larger dose or a finer grind produce greater

flow resistance and a slower flow rate.

Water always follows the path of least resistance through the coffee bed; it is

the barista’s job to create not only the proper amount of flow resistance, but also to

form the coffee bed such that it provides uniform resistance to the water. A poorly

formed coffee bed is vulnerable to the creation of a channel, an area of high-velocity

flow through the coffee bed.

Channels are detrimental to brew strength and flavor. The large volume of water

flowing through a channel dilutes the shot and causes the grounds along the channel

to overextract,* increasing bitterness. Because less water passes through the

denser areas of the coffee bed, those areas underextract,* resulting in underdeveloped

flavors and lower brew strength. To minimize channeling, a barista should

prepare a bed of grounds so it has a smooth and level surface, forms a tight seal with

the wall of the portafilter basket, and is of uniform density.

Evidence of channeling can sometimes, but not always, be seen when using a

bottomless portafilter. Channeling is indicated when extract flows more rapidly or

yellows more quickly from some areas of the basket than others.

The Barista’s Role

When preparing an espresso, a barista’s basic goals should be to:

• Create a dose of consistent mass every shot.

• Choose the grind setting that will provide the desired flow resistance.

• Distribute the dose evenly to provide uniform resistance to the water.

• Tamp with enough pressure to eliminate void spaces within the coffee bed and

to seal the surface of the bed.

• Ensure the brewing water is of the desired temperature.

• Complete all of these tasks efficiently.

The Grinder’s Role

The grinder is the most important piece of equipment in an espresso bar. Grinders

are usually overshadowed by more expensive, flashier espresso machines, but

* The terms “overextract” and “underextract” are subjective; by using them I do not mean to imply

there is a universally agreed-upon ideal level of extraction for coffee, tea, or espresso. Instead, the

reader should interpret overextraction as a general reference to extracting more than the intended

amount, usually to the point of excessive bitterness or astringency. Underextraction is meant to

indicate less extraction than intended, usually such that the resulting beverage has insufficient

flavor development.

4 Espresso

The yellow extract on the left indicates channeling.

grinder qualit~· is arguably the single most important factor in preparing a great

espresso.

A quality grinder must:

Produce the proper particle sizes to provide adequate flow resistance.

Create a bimodal or trimod(l/ distribution of particle sizes. (See “Grinding for

Espresso” in Chapter 2.)

Cause minimal heating of the grounds during grinding.

Limit the production of fines.

Fines play many impmtant roles in espresso percolation; these will be discussed

in detail in Chapter 3. For now it is impo1tant to know that the brewing water can

transp01t and deposit fines lower in the coffee bed during percolation, a phenomenon

known as.fines migration. When fines and large insoluble protein molecules

are deposited at the bottom of the coffee bed they can form a compact layer,’ or

densely packed solid mass. A compact la~·er clogs holes at the bottom of the filter

basket and can result in obstruction of flow paths, uneven resistance to flow, and

channeling. It is desirable to have some fines. but too many fines or too much fines

migration can damage espresso quality.

‘/11eE spresso M<1chi1\1 eR ole

The espresso machine’s task is to deliver water to the grounds in a predetermined

pattern of temperatures and pressures. These patterns are known as tempemture

/J/'{?fi/esa nd p1·essw·e pmfiles.

A quality espresso machine should be able to produce consistent temperature

and pressure profiles every shot. ewn under heav~· use.

5

The Phases of Espresso Percolation

1. Preinfusion. Once the pump is engaged, the first phase of espresso percolation

is a brief, low-pressure preinfusion. (Some machines skip this step and

go directly to the second phase.) During preinfusion the grounds are wetted

by a slow, low-pressure flow, which allows the coffee bed to reorganize itself

and create a more even flow resistance.

2. Pressure increase. In the second phase, the pressure increases, compacting

the coffee bed and increasing the flow rate. Machines without a preinfusion

cycle start at this phase; such machines can make great espresso, but they are

more fickle and less “forgiving” of inconsistencies on the part of the barista.

3. Extraction. In the third phase, extraction begins, and espresso flows from

the filter basket. Extraction is primarily accomplished by the washing, or

erosion, of solids from the surfaces of the ground coffee particles by the

brewing water.

The eluted extract starts out relatively dark and concentrated with solids and becomes

more dilute and yellow as extraction progresses. Throughout extraction,

solids are removed from the coffee bed in a mostly top-down fashion; solids are

preferentially removed from the upper layers of grounds. As solids are transported

through the coffee bed, some settle lower in the bed, some get deposited in the compact

layer, and others get extracted from the bed into the cup.

Brew Strength and Yield: Espresso

The brew strength of an espresso refers to its concentration of solids, which is between

20-60 mg/ml when using traditional Italian standards. 9 The solids yield of

an espresso is the percentage of mass removed from the grounds during extraction;

solids make up about 90% of the extracted material in an espresso. 9 Please

note: when discussing espresso it is common to refer to solids concentration and

solids yield, whereas when discussing drip coffee it is more appropriate to focus on

solubles concentration and solubles yield.

Brew strength and yield have no direct relationship. For instance, using higher

water temperature simultaneously increases brew strength and yield, while running

extra water through a bed of grounds decreases strength and increases yield.

Grinding for Espresso

Grinding is the fracturing of coffee bean particle cells. Its purpose is to increase the

amount of coffee solids exposed to the extracting liquid.

Why Espresso Requires a Very Fine Grind

Quality espresso requires an exceptionally fine grind for numerous reasons.

• It creates particles with extremely high specific surface area, a prerequisite for

rapid washing of large quantities of solids from the particle surfaces.

• It opens more particle cells, which allows more large molecular solubles and

colloidal material to be transferred to the extracting liquid. 7

6 Espresso

• It accelerates wetting (and diffusion, if it in fact occurs) by providing a shorter

average path for water entering cells and solubles diffusing out of cells.”

The greater specific surface area of smaller particles, along with their ability

to pack together more tightly, provide the hydraulic resistance necessary for

proper flow rate through the coffee bed.

G,-i11dePr e1fonna11ce

I recommend you invest in the best grinder you can afford, even if it means you

have to buy a cheaper espresso machine. A mediocre grinder under heavy use can

damage flavor with excessive heat and can prevent even extraction by producing

clumps, too many fines, or poor distribution of grounds in the basket. No espresso

machine, no matter how impressive, can (yet) compensate for the problems created

by poor grind quality.

The single most important feature a grinder can have is shm·p burrs. This cannot

be overemphasized. Sharp burrs create less strain on a grinder’s motor,- generate

less heat, produce fewer fines, and offer better particle size distribution.”

Because it can be expensive to regularly purchase new burrs, I recommend you find a

local machine shop or grinder manufacturer willing to resharpen dull burrs. Burrs can

be resharpened several times before they need to be replaced.

Espresso 7

How to Evaluate a Grinder

A home barista who rarely pulls more than two or three shots in an hour will probably

not notice much difference in the performance of various professional-quality

grinders. A home barista also has the luxury of using a time-consuming method

such as the Weiss Distribution Technique to compensate for poor grinder performance.

(See “Grooming” in Chapter 2.) Therefore a home barista can achieve consistently

excellent results with any professional grinder of reasonable quality.

On the other hand, a barista who works in a cafe and frequently pulls several

shots in quick succession needs to be more careful when choosing a grinder. A

professional barista needs a grinder that facilitates even distribution and does not

overheat the grounds when under heavy use.

The following are some important criteria for evaluating a grinder.

Minimal heating of the grounds. Some heating of the grounds is inevitable

during grinding due to friction and the breaking of molecular bonds, but additional

heating of the grounds due to contact with very hot grinder surfaces is undesirable.

Such heating can damage coffee flavor and accelerate the loss of aromatics. 1t

can also cause oil to bleed to particle surfaces, creating sticky clumps of grounds,*

which leads to erratic percolation. 9 Clumps resist wetting and can cause large sections

of the coffee bed to remain dry throughout percolation.

A well-designed grinder should have no small, enclosed spaces that trap and

build up heat during heavy use. Sharper burrs, lower rotation speeds, and larger

“functional” burr surfaces also mitigate the heating of the grounds during grinding.

I refer to functional burr surfaces because in some grinders much of the burr

surface is useless, due to the burrs being too far apart to crush the beans. The larger

the functional surface, the better the heat dispersion during grinding.

Appropriate particle size distribution. Commercial espresso grinders are

designed to yield bimodal ( or trimodal) particle size distribution. This means the

greatest frequency of particle sizes is clustered around two (or three) particular

values. In such a distribution the coarser particles serve to allow proper flow, while

the finer particles provide the large amount of specific surface area necessary for

rapid extraction. 9 As mentioned previously, sharp burrs are necessary to optimize

particle size distribution; dull burrs create a more uniform distribution of sizes.

No clumping. A grinder must be able to dispense grounds without clumps. To

test your grinder, dose a couple of shots’ worth of grounds onto a piece of paper

and search the pile for clumps. If there are any, clean the burrs as well as the passageway

between the burrs and the dosing chamber, and replace the burrs if they

are worn. If the grinder still creates clumps, try the Weiss Distribution Technique.

(See “Grooming” in Chapter 2.)

Clumping is caused by excessive heat generation during grinding, a grinder design

that forces the grounds to squeeze through a small passageway between the

* I had this problem once due to using small, dull, flat burrs; upon inspecting the spent coffee pucks,

I found that 20%-25% of each puck was still completely dry!

8 Espresso

burrs and dosing chamber, or by particles with a lot of surface oils due to aging or

dark roasting.

Ease of uniform distribution. Many baristi have come up with ingenious ways

to improve distribution while dosing, but a good grinder should not be so dependent

on a barista’s skill to achieve uniform distribution.

Some dosing mechanisms facilitate uniform distribution, while others make

good distribution so difficult that even the most skilled barista has difficulty achieving

it. Good distribution is easiest with grinders that drop grounds vertically as

opposed to diagonally into the portafilter, dispense “fluffier” grounds, or have a

homogenization (blending) mechanism.

Grinding Systems: Pregrinding Versus Grinding To Order

Most commercial grinders are designed to pregrind, with the dosing chamber kept

full of grounds so the barista simply needs to pull the lever one or two times to dose

the required amount of grounds. This system is very fast and convenient, but it has

two significant flaws: first, the weight of each dose is affected by how much ground

coffee is in the dosing chamber, and that amount constantly varies. Second, the ebb

and flow of business causes the grounds to spend a variable amount of time degassing

after grinding and before infusion.

Degassing is the gradual release of gases, primarily CO, plus some volatile aromatics,

produced during roasting.* Once coffee is ground, degassing dramatically

accelerates.

The amount of CO, in the grounds is important because it influences flow rate

during percolation. When hot water contacts the grounds, they vigorously release

CO,,:t. which repels the surrounding liquid and increases flow resistance, slowing

the flow rate.

The pregrinding system results in inconsistent flow rates because shots are

made from grounds containing variable amounts of CO2

Inconsistent flow rates in

turn cause flavor, body, and brew strength to vary.

Grinding to order is superior to pregrinding. Grinding coffee freshly for each shot

preserves more aromatics and produces more consistent flow rates because shots

are made from grounds with a consistent amount of CO,. The only disadvantage of

grinding to order is that it requires more time and attention to make each shot.

* One gram of freshly roasted Arabica coffee beans contains 2-10 mg of CO2 ,14 with most reported

values in the low end of the range. In whole bean form it takes several weeks for the bulk of the CO2

to be released; in ground form coffee degasses many times faster. One study demonstrated that

45% of the CO2 held in freshly roasted beans was released within the first five minutes after grinding.”‘

A typical espresso grind, finer than that used in the study, would release CO2 even faster.

* At espresso brewing temperatures, CO2 is more water soluble at higher pressures than at lower

pressures. During espresso percolation the pressure is highest at the top of the coffee bed (typically,

9 atmospheres) and lowest at the bottom of the coffee bed (atmospheric pressure). The

brewing liquid encounters progressively lower pressures as it descends the coffee bed; therefore,

the preponderance of outgassing occurs in the lower coffee bed. A lot of outgassing can also occur

throughout the entire coffee bed during low-pressure preinfusion.

Espresso 9

A boristo should rarely adjust the grind more than one notch at o time.

Adjusting the Grind

During the normal course of business, the most important factors affecting flow

rate from shot to shot are the grind and dose. Varying the dose by only 1 gram can

alter the flow rate for a given shot volume by several seconds. Therefore, a barista

should not adjust the grind in response to just one shot with poor flow rate if there

is a chance the dose was not identical to that of previous shots. On the other hand,

whenever the flow rate has trended faster or slower over the course of several shots,

the barista should feel confident the grind needs adjusting.

To achieve consistent dosing a barista should:

1. Practice the same exact dosing, distribution, and grooming (leveling and

refining of the distribution) techniques every shot.

2. Practice until he or she can consistently create a coffee bed with a variation

in mass of only about 0.5 gram.

3. Periodically test his or her consistency by weighing a few doses during a

busy period.

It is best to adjust the grind in small increments. lf your grinder has a small tunnel

between the burrs and the dosing chamber, any new grind setting should not be

evaluated until the first 5 grams or so of grounds have been used or discarded. This

eliminates any effect caused by “old” grounds that had been stuck in the tunnel or

scattered around the dosing chamber.

Espresso

Dosing and Distribution

Unlike many other coffee professionals, I consider dosing and distribution a unit,

since the distribution of most of the coffee bed is determined during dosing. A barista’s

goal when dosing and distributing should be to provide every shot with a dose

of identical mass and evenly distributed volume and density. Dose size variation

leads to inconsistent flow rates, and uneven distribution causes uneven extraction.

Perhaps the single most important skill a barista can have is to be able to consistently

create an evenly distributed coffee bed. Distribution starts as soon as dosing

begins, so it is critical to dose with careful aim.

How to Dose

The following is one example of a dosing system.

1. Unlatch the portafilter from the espresso machine.

2. Knock out the spent puck.

3. Wipe the inside of the portafilter basket with a dry rag; moisture on the side

of the basket can promote channeling around the edges of the coffee bed.

4. Ensure all of the basket holes are clear.

bSJJl'<!SSO 11

5. Turn on the grinder. If you have a very slow grinder, you may turn on the

grinder as the first step.

5. Pull the handle repeatedly while rotating the portafilter so that the grounds

fill the basket as evenly as possible. If more grounds fall into one section than

another, the favored section will be more compacted, even after grooming.

7. Turn off the grinder when the proper amount has been ground.

8. Stop dosing when the desired amount is in the basket. This amount can be

exactly the amount used for extraction, or it can be a little more, with the

extra grounds removed during grooming. Whatever amount you choose, it

is important to consistently dose the same amount every shot.

Dosing Var·iations

No matter what dosing method you use, it is easier to get a uniform distribution by

sprinkling a small dose with each pull of the handle than by dumping large amounts

of grounds with each pull. A couple of common dosing methods are efficient enough

to use in a busy cafe.

1. The pie piece method. Think of the coffee bed as a pie cut into several wedgeshaped

pieces. As you dose, fill each “pie piece” to the rim of the basket,

rotate the portafilter and fill in the adjacent piece, rotate and fill again, and

soon.

2. The layering method. Sprinkle small amounts around the basket while continually

rotating it to form a shallow, even layer of grounds. Repeat the process

to build a second layer on top of the first. Continue stacking layers until

the desired dose is in the basket.

Constantly rotate the portofilter bock and forth (not shown) to create layers. Always aim doses

at the lowest spot on the surface of the bed.

12 Espresso

Grooming

After dosing and before tamping, a barista should groom the dose. Grooming involves

redistributing the upper layers of the coffee bed (or, in the case of the Weiss

Distribution Technique, the entire coffee bed), eliminating any extra grounds if the

barista deems the dose too large, and then polishing the surface of the coffee bed

before tamping.

Grooming Methods

Several common grooming methods are in use today, each with its own advantages

and disadvantages.

1. The NSEW (No1·th South East West) Method (not to be confused with the

tamping method of the same name). The NSEW method is easy to learn and

fast enough for use in a busy cafe.

Using your finger or a straight-edged tool, push the mound of grounds

toward the far rim of the basket (i.e., “north”) without pushing the grounds

over the edge. Then push the mound to the near edge (“south”), then to the

right, then to the left. Finally, push any extra grounds over the edge. The

surface of the bed should be smooth and level, with no divots or visible

inconsistency. Using the NSEW method, it is critical that the amount of

“extra” grounds in the basket prior to grooming is consistent every time.

The mass of the mound before grooming heavily influences the density of

the groomed bed. The end result might always look the same, but a bed

that began with a larger mound of grounds before grooming will be denser

after grooming.

First push the grounds to the for rim of the basket [north), then bock toward the handle [south),

then right (east), then left (west), pushing any extra grounds over the edge before tamping.

2. Stockfleth’s Moue. Stockfleth’s is perhaps the most difficult grooming technique

to master but works well once you get the hang of it. Begin by slightly

overdosing the basket. Hold the portafilter in front of your torso with both

elbows facing outward. Put a straightened finger, or the webbing between

the thumb and forefinger, gently on the grounds. Pull both elbows inward,

causing the portafilter and the leveling hand to rotate in opposite directions.

The mound of grounds should rotate around the center point of the

Espresso

Begin with the elbows out, and pull the elbows in while rotating the mound of grounds around

the center of the coffee bed. Repeat this motion two or three times.

Perform a NSEW swipe before pushing any extra grounds over the edge of the basket.

14 Espresso

basket. Repeat the motion several times until all areas are equally filled and

compacted. You may polish the surface with a quick NSEW swipe before

pushing any residual grounds over the edge.

3. The Weiss Dish·ibution Technique (WDT). Invented by John Weiss, the WDT

is an ingenious way to compensate for clumps or uneven distribution. To execute

the WDT, squeeze a funnel into the top of the portafilter basket. (John

recommends using a small yogurt container with the bottom cut off.) Funnel

the grinds into the basket until it is slightly overfilled. Stir the grounds

well with a slender, pointed object such as a dissecting needle or straightened

paper clip. Remove the funnel, groom the dose with a quick NSEW swipe or

Stockfleth’s Move, and tamp. Alternatively, the grounds can be dosed into a

separate container and stirred before being poured into the portafilter basket.

This version has the advantage of allowing the portafilter to retain more

heat, since the portafilter spends less time detached from the group head.

The WDT offers the two unique benefits of breaking up clumps and

redistributing an entire dose after it is already in the basket. The disadvantage

of the WDT is that it might be too time consuming for regular use

in a busy cafe.

Ugh! Lots of clumps. Stir the grounds vigorously with a straightened paper clip to break up the

clumps. The end result is fluffy, clump-free grounds.

Grooming Shallow Doses

All of the above grooming methods require starting with a mound of grounds large

enough to fill the basket to the rim. Doses too small to crest the rim cannot be

groomed with a level finger or tool. To groom a smaller dose, a barista has two

choices: groom with a rounded tool or switch to a smaller basket.*

* Grooming with a convex tool results in a coffee bed with a concave surface. After tamping. such a

bed is denser near its perimeter than its center. This uneven density is not ideal. However, because

channels most frequently form near the perimeter of a coffee bed, such a distribution eliminates

the most common source of channeling. A coffee bed groomed with a convex tool usually results

in good. but imperfect, extraction patterns, and rarely forms large channels.

Espresso 15

Use the lid of the dosing chamber or any other curved object to groom shallow doses. The

greater the curvature {i.e., the smaller the object, if it is circular), the smaller the resulting dose

will be.

Shallower doses can be groomed with a rounded, convex tool such as the lid of a

grinder’s dosing chamber. One option is to rest the object on the rim of the basket

and swipe NSEW before pushing any extra grounds over the edge. Alternatively,

swipe the tool until it is at the centerline of the basket, and then rotate the tool one

or two revolutions in a fashion similar to Stockfleth’s Move. Residual grounds can

then be swiped over the edge with the rounded object.

Using a smaller basket can eliminate the need for a special grooming tool. For

instance, a 15-gram dose might be shallow in one double basket but will be level

with the rim in a different manufacturer·s double basket. If you prefer to always

groom with a level tool, it is worth having a variety of baskets on hand.

Tamping

Tamping locks in a distribution, polishes the surface of the coffee, and eliminates

any large void spaces in the coffee bed. Tamping also offers a perceptive barista

feedback about dose quantity, distribution, and grind.

How Ha,.d to Tamp

Contrary to popular belief, the difference in flow resistance caused by lighter and

harder tamping is minimal.q Once the coffee has been tamped with enough pressure

to eliminate any large void spaces in the bed, additional tamping pressure ,..viiin ot

16

have much effect on extraction quality or flow rate.* Two factors account for this.

1. Some or all of the pressure generated by tamping is immediately relieved

when the coffee particles are wetted.

2. The 50 lb or so of force applied by a barista when tamping firmly is dwarfed

by the 500+ lb of force applied by the pump during extraction.*

Very firm tamping does not seem to offer any benefits, but there are at least two

reasons to tamp lightly: it causes less stress on the barista’s wrist and shoulder, and

it makes it easier for the barista to achieve a perfectly level tamp. (This is immediately

clear when using a tamper and basket designed to have a very tight fit. When a

barista tamps with a lot of force they will get stuck together much more frequently,

indicating the tamper is not level.)

* One interesting reason many ba1isti overestimate the impact of harder tamping on flow rate is

that, for a given dose and basket, a harder tamp \,viii compact the bed more, leading to more

“headspace” between the grounds and the dispersion screen. Because the entire headspace must

be filled with water before the water will percolate through the grounds at full pressure, the extra

headspace increases the lag time between pump activation and the appearance of extract from

the portafilter. The extra lag time might lead a barist,1 to overestimate how much the harder tamp

slowed the flow rate.

*9 bar pressure z 130.5 psi; coffee in 58-1110b1a sket has surface area of 4.09 sq in: 130.5 psi x 4.09

sq in= 533.7 lb.

Espresso 17

To Tap or Not to Tap?

A recent point of contention in the tamping debate is whether to tap the side of the

portafilter between tamps. The argument in favor of tapping is that it dislodges any

loose grounds which had crept up the walls of the basket during the first tamp, and

those grounds can then be sealed into the coffee bed with a second tamp.

It is hard to see how incorporating a few loose grounds into the coffee bed is

worth the potential harm done by tapping. The tap can break the seal between the

grounds and the wall of the basket, creating an easily exploitable channel around

the edges of the coffee bed. In my experience a broken seal is difficult, if not impossible,

to fix with a second tamp. It might be possible to tap without breaking

the seal, but tapping does not seem wo1th the risk. The bottom line: a few loose

grounds are a minor problem, if in fact they are a problem at all. (I don’t think they

are.) A broken seal between the grounds and the basket is a major problem.

One barista I admire taps with her wrist (an action akin to a strike with a “dead

blow” hammer) in order to limit any jarring of the coffee bed. If you must tap, this

seems to be a safer method than tapping with the hard handle of a tamper.

How to Tamp

Grip the tamper loosely in your hand, aligning the shaft of the tamper handle as if

it were an extension of your forearm. Your wrist should be neutral, and the base of

the tamper handle should sit comfortably in the hollow of your palm. This position

will minimize strain on the wrist, which is critical for a barista who tamps hundreds

or thousands of times per week.

Keeping the tamper level, squeeze it gently onto the grounds. That’s it. There is

no need for a twist or a second tamp.

When you release the tamper some loose grounds might remain on the wall of

the basket or on the surface of the coffee bed. Briefly turn the po1tafilter upside

18

Hold the tamper comfortably in the hollow of your palm with the shaft of

the tamper handle aligned as on extension of your forearm.

Esp,·esso

Tamp lightly with a neutral wrist to minimize strain.

The tamped coffee should have a smooth and level

surface.

down if you wish to get rid of these grounds. Next, wipe the edges of the portafilter

clear of grounds. Last, latch the portafilter onto the espresso machine gently

in order to avoid jolting the grounds and breaking the seal between the coffee and

the basket.

Perform the above actions quickly but carefully to prevent the portafilter from

losing too much heat while it is unlatched from the group head.

Espresso 19

The Tamper

The tamper should fit snugly into the portafilter basket. If the tamper is too small it

will not seal the perimeter of the coffee bed, and channeling around the edges of the

bed is more likely to occur. Ideally, the tamper should fit such that if it sits the least

bit crooked, it will get stuck in the basket. I have had numerous tampers machined

to fit my baskets and so far have found the ideal gap between the tamper and basket

to be ‘i/1000 inch, i.e., a difference of rn/1000 inch (.25 mm) in diameter. A larger gap

will create a slightly higher frequency of channeling over the course of many shots.

Custom tampers can be made by a local machine shop or by a tamper manufacturer

willing to make custom sizes.

Whereas most commercial tampers are machined precisely, portafilter baskets can

vary tremendously in size; in a recent batch of triple baskets I bought from one supplier,

the diameters varied within a range of 75/1000 inch, or 2 mm! I have found it is

easy to find double baskets of consistent size and tampers designed properly to fit

those baskets; I’ve had less luck with triple baskets. For triples my strategy has been

to order dozens of baskets, measure their diameters to within 1/1000 inch, and return

the baskets of exceptionally large or small diameter. Usually, the majority of basket

diameters will be within a range of 2/1000 inch to 3/1000 inch; those are the ones I keep.

Then I have a tamper machined to a diameter 10/1000 inch smaller than the smallest

diameter in the range.

Please note: a standard 58-mm tamper designed for single and double baskets

does not fit all baskets equally and is not designed for use with triple baskets.

Water Temperature

Brewing water temperature is very important because it affects flavor, brew strength,

and flow rate. The “ideal” brewing temperature is determined by numerous variables,

including the coffee used, the flow rate of a shot, and, most importantly, your

taste. It is fair to say almost all professionals prefer temperatures in the range of

185°F-204°F.

A few established facts exist regarding the relationship between temperature

and espresso quality.

• Excessively low temperatures produce sour, underextracted espresso.

• Excessively high temperatures produce bitter, acrid, and woody flavors.”‘

• Higher temperatures result in more solids extraction and body.”‘

• Higher temperatures result in slower flow rates. 9

Managing Brewing Temperature

Before pulling a shot, a barista should purge, or flush, water from the group head

to clear coffee particles from the dispersion screen and to manipulate brewing temperature.

A flush can be done with the portafilter removed or with an empty portafilter

latched onto the group head.

Some flushes are done to cool the group, some to preheat the pipes feeding the

20 Espl’!!SSO

Flushing with no portofilter. Flushing

can also be done with on empty portafilter

in place to preheat it.

group head, and others to purge the heat exchanger of overheated water. Every machine

is different and requires a customized flushing routine based on the machine’s

design, the desired brewing temperature, the pressurestat setting, and other factors.

Managing Tempemru.re on Multiple-Boiler Machines

Multiple-boiler machines have one boiler dedicated to steam production and one

or more thermostatically controlled boilers dedicated to brewing water. If it is welldesigned

and has a PlD (proportional integral derivative) controller, a multipleboiler

machine can produce extremely consistent brewing temperature every shot.

Such machines usually require a very short purge to produce the desired brewing

temperature. The temperatures resulting from various purge amounts should

be measured using a Scace Thermofilter or other bead probe thermometer.

Espresso

The Scace Thermofilter and Fluke”” multimeter

21

The temperature profile produced by a thermostatically controlled machine is

considered “flat” and looks like an “L” rotated clockwise 90°. Depending on the machine,

it takes between a fraction of a second and several seconds for the brewing

water to reach a constant temperature.

……

IL,

.0. ….

Q.j. . .:.::., ,

.R.I. Qj

C.

E

Qj

I-

0

FLAT VERSUS SPIKED TEMPERATURE PROFILES

5 10 15 20

Seconds

Managing Temperature on Heat-Exchange Machines

25

Spiked

Profile

Flat

Profile

In heat-exchange machines, cold water is drawn through the heat exchanger, a small

pipe within the boiler where water is flash-heated on its way to the group head. Most

heat-exchange machines have a thermosyphon loop in which water circulates between

the heat exchanger and group head. This keeps the group head hot and keeps

the water cooler than it would be if it were to stagnate in the heat exchanger.

Heat-exchange machines do not dispense brewing water at a constant, or flat,

temperature. Instead, as shown in the illustration, the temperature increases sharply

over the first few seconds of a shot, peaks, stabilizes, and then drifts lower.*

Managing temperature on most heat-exchange machines requires three steps.

Step 1: Adjust the pressurestat. The pressurestat controls the pressure, and

hence temperature, in the boiler; higher pressure leads to higher temperature. The

pressure should be set low enough to limit overheating (relative to the desired temperature)

of the brewing water but not so low as to compromise milk steaming pressure.

If you choose to use very low boiler pressure, please note that you might need

to switch to steam wand tips with smaller holes in order to maintain enough steam

velocity to produce quality milk froth.

* Heat-exchange machines dispense water at a wide range of temperatures over the course of a shot.

When I refer to a heat-exchange machine as being consistent within 1°F shot to shot, it means if

you mapped the temperature profile graphs of several shots on one grid, the curves would consistently

be within 1 °F of each other.

22 Esp,·esso

Most stock pressurestats allow the boiler pressure to fluctuate by about 0.2 bar,

causing temperature fluctuations of approximately 4 °P. More consistent boiler

temperatures can be achieved by decreasing the pressurestat’s deadband, if it is

adjustable, installing a more sensitive pressurestat, or installing a PID controller.

(See the discussion of PIDs later in this chapter.)

Step 2: Adjust the thermosyphon flow restrictors, if there are any. Thermosyphon

flow restrictors improve temperature consistency from shot to shot and

limit the amount of cooling flush needed. The right combination of pressurestat

setting and flow restrictor size in conjunction with a very short flush will allow a

barista to consistently achieve any reasonable brewing temperature range with

variations of less than 1 °P shot to shot.

Please note: some restrictors are adjustable; others need to be replaced with a

different size to alter brewing temperature.

Step 3: Temperature surfing. Heat-exchange machines without flow restrictors

require much more effort on the part of the barista to achieve acceptable temperature

consistency. These machines require the barista to adjust the length of the

flush to the conditions of each shot, a technique known as temperature surfing.

To temperature surf, first flush beyond the point when the brewing water

changes from sputtering (boiling) to quietly flowing, and then allow the water to

run a few seconds more. The end of the sputtering indicates the heat exchanger has

been fully flushed. The longer the water is allowed to flow, the cooler it will get, up

to a point. As soon as the flush is halted, the water in the heat exchanger will begin

to reheat. Therefore, to achieve the desired brewing temperature, a barista has to

consider both the length of the flush and the time of the pause between the flush

and pulling the shot.

For efficiency in a busy cafe, a flushing routine should be designed with minimal

pause time, a technique is known as “flush and go.” This consists of flushing down

to the desired brewing temperature and then immediately latching on the portafilter

and engaging the pump. Home baristi without concern for expediency have the

luxury of experimenting with various combinations of flushes and pause times.

It is useful to accurately measure the temperatures produced by various flushing

routines before settling on one. The easiest way to do this is by using a Scace Thermofilter.

Other high-speed bead probe thermometers also work, but they require

a fresh dose of grounds per shot to create the realistic flow resistance required for

accurate temperature measurement. That can quickly make temperature measurement

messy and expensive.

Spiked Versus Flat Temperature Profiles

Many coffee professionals have expended a lot of energy debating the merits of

spiked versus flat temperature profiles. There is little doubt the two types of temperature

profiles result in modestly different flavors in the cup. However, with all

machines, extraction takes place at a wide variety of temperatures throughout the

coffee bed, especially in the earlier stages of extraction. This is because the grounds

absorb heat from the brewing water as it descends the coffee bed. This fact alone

makes it hard to justify many baristi’s slavish devotion to flat temperature profiles.

Espresso 23

Many baristi prefer flat temperature profiles because they are easier to comprehend

and reproduce. Spiked profiles are harder to replicate from shot to shot and

from one machine to the next, but the bottom line is the “best” shot each profile is

capable of producing is quite similar.

If you are feeling super geeky and have an extra few hundred bucks lying around,

you can buy a Scace Thermofilter, a digital thermometer, and datalogging software

and play with your machine’s temperature profiles. To learn how to do this, refer to

some informative discussions at www.home-barista.com. Go to “forums” and search

for “datalogger scace fluke.”

Proportional Integral Derivative Controllers

Recently PID controllers have been installed in espresso machines to precisely control

brewing temperature. A PID controller works by fine-tuning the on/off cycling

of the heating element.*

In a multiple-boiler machine the PID acts directly on the brewing water boiler as

a precision thermostat and can consistently produce brewing temperatures within

a few tenths of one degree. If you are willing to spend $6,000 to $10,000 for a

multiple-boiler espresso machine, I recommend you spend an extra few hundred

dollars on a PID to greatly improve temperature stability.

In a heat-exchange machine a PID controls brewing water temperature indirectly

by maintaining a consistent boiler temperature, in turn making the effect of

the heat exchanger more consistent. Installing a PID in a heat-exchange machine is

arguably a waste of money since a reliable, precise pressurestat can achieve a comparable

level of temperature consistency at much less cost. A PID does, however,

provide real-time boiler temperature readings and a quick, convenient means of

changing temperature settings without any guesswork.

Dispensing Temperature Versus Extraction Temperature

The temperature of the brewing water as it leaves the dispersion screen (dispensing

temperature) and the actual temperatures at which the grounds extract (extraction

temperature) are quite different. Many baristi obsess over dispensing temperature

but don’t think much about extraction temperatures. But of course extraction temperature

is what determines the flavor of an espresso.

Why are they different? At the beginning of an extraction the grounds, basket,

and portafilter absorb heat from the water, causing extraction temperatures to be

* A PID controller uses a feedback loop to control the output of the heating element based on calculations

involving the “error,” or the difference between the actual boiler temperature and the desired,

or setpoint, boiler temperature. The PID calculates the output based on three parameters: P

(proportional), I (integral), and D (derivative). The proportional calculation adjusts output based

on the magnitude of the error, the integral action is based on the duration (time) of the error, and

the derivative action is based on the rate of change of the error.

24 Espresso

lower than the dispensing temperature. As an extraction progresses the coffee bed

gets warmer and extraction temperatures increase, eventually approaching the dispensing

temperature if enough water is run through the grounds.

The major influences on extraction temperature are:

1. Dispensing temperature. This is the dominant influence and is approximately

the upper limit of extraction temperature.

2. Portafilter mass and temperature. A cold portafilter can dramatically decrease

extraction temperature. To keep the portafilter hot, minimize the amount of

time it is detached from the group head during dosing and tamping.

3. Grounds temperature. This factor does not vary much from shot to shot,

since almost all cafes store beans at room temperature and almost all grinders

dispense grounds at just above the ambient temperature.

4. Mass of the grounds (dose). The larger the mass of grounds, the more heat

they will absorb from the water and the lower the initial extraction temperatures

will be.

5. Mass of the water. The more water passed through a given mass of grounds,

the higher the average extraction temperature will be.

Putting It All Together

Up to this point we have analyzed the various details of espresso making in isolation.

I would now like to put all the parts together and describe the process of

pulling a shot. Please note that this is merely one sample system; your particular

equipment might necessitate a slightly different order of tasks. For instance, if you

have a very slow grinder, your first action might be to turn on the grinder.

1. Unlatch the portafilter.

2. If your machine requires a long flush, start flushing now. Stop the flush

when appropriate.

3. Knock out the old grounds.

4. Wipe the portafilter basket clean and dry. Ensure all basket holes are clear.

5. Turn on the grinder. (If you have a very slow grinder, you may turn on the

grinder as the first step.)

6. Begin dosing. Rotate the portafilter while dosing to distribute the grounds

evenly throughout the basket as it fills.

7. Turn off the grinder when you estimate the proper amount has been ground.

8. Finish dosing.

9. Groom the dose.

10. Be sure the tamper is dry and free of grounds.

11. Tamp lightly.

12. Wipe any loose grounds from the rim of the portafilter basket.

13. If your machine requires a very short flush, do it now.

14. Latch on the portafilter and engage the pump.

15. Observe the underside of the bottomless portafilter. If there is immediate

channeling, consider the possible cause, address it, and return to step 1.

16. Stop the flow based on your desired shot volume or color.

Espresso 25

17. Serve the shot immediately.

18. If the flow rate was faster or slower than desired, consider whether to adjust

the grind.

What Does a Good Pour Look Like?

A barista cannot know how an espresso will taste by simply looking at the pour.

However, once a barista is intimate with a particular coffee and machine, he or she

can use visual cues to estimate shot quality.

The following guidelines represent a useful framework for judging shots visually.

The progression of flow and color should be adjusted to your particular coffee

and machine. All observations assume use of a bottomless portafilter.

If there is a preinfusion phase, once the pump is activated it should take 3-10

seconds for coffee to appear on the underside of the basket. If there is no preinfusion,

the extract should appear after 2-5 seconds. Either way, we’ll consider the

first appearance of coffee to be time zero.

During the first 2 seconds, dark brown extract should appear from all of the

holes on the underside of the basket. If coffee has appeared from some, but not all,

of the holes in the first 2 seconds, it is evidence of uneven extraction.

Seconds 3-5 should see viscous brown drops of espresso fall from the basket.

Any yellow at this stage indicates a channel has formed, the grind is too coarse, or

the extraction temperature is inappropriate.

By 8-12 seconds, all of the drops of espresso should join into one brown/ orange

stream.

The color will become progressively more yellow during the rest of the flow. The

full shot should be completed in 20-35 seconds, depending on the desired espresso

brewing ratio and flavor profile.

26 Espresso

Preinfusion

Preinfusion is a brief wetting of the grounds at low pressure prior to engaging consistent

full pressure. Numerous coffee professionals, including me, have found that

most forms of preinfusion, on most machines, decrease the incidence of channeling

and make the espresso machine more forgiving of flawed distribution, tamping, or

grind setting.

Why Preinfusion Wo,.ks

The low pressure of preinfusion wets the grounds with a slower liquid flow than

would be the case if the grounds were wetted at full pressure. The slower flow allows

the grounds to swell, redistribute themselves, and become more adhesive before

full pressure is applied. This provides two important benefits.

1. A decrease in the frequency of channeling. I’ve found this to be true with

numerous machines; it is also consistent with the finding that “prewetting”

(preinfusion) decreases channeling in packed percolator beds.7

2. A decrease in fines migration. Because fines migration is proportional to

flow rate,’ wetting with a slower flow causes more fines to get trapped by

the swelling and adhesiveness of the surrounding grounds before the fines

can migrate to the bottom of the coffee bed. As noted earlier in this chapter,

limiting fines migration helps promote more even extraction.

Espresso 27

I want to be clear about this because it is controversial: Using preinfusion will not

necessarily make your best shot better, but it will almost certainly result in a much

higher frequency of great shots. Even a talented, experienced barista will find that

preinfusion improves his or her consistency. More importantly, in a busy cafe with

many baristi of different skill levels, preinfusion will lead to more consistency, a

higher frequency of quality shots, and less fussing with grind adjustments.

Common Preinfusion Methods

There are numerous methods of preinfusion. As long as a preinfusion method involves

low-pressure infusion followed by an uninterrupted increase in pressure, it

is probably beneficial to use. The following are some of the most commonly used

methods:

Manual preinfusion. The barista begins infusion at low pressure and controls

when to engage full pressure. This is a feature of lever machines and some semiautomatic

machines.

Manual preinfusion requires experimentation to determine the best combination

of preinfusion time and pressure. A good starting point is to set the line pressure

feeding the espresso machine to 3.5-4.5 bar (51-65 psi), and to sample the

results produced by preinfusion times ranging from 3-10 seconds.

How the triple ristretto was born (a fictional story):

A long time ago, in a little town in the hills near Trieste, many old Italian men gathered every morning

at Hilly Caffe to argue and gesticulate wildly while drinking beautiful, small cappuccini. This went on

for many decades, and the men were happy because they thought the cappuccini at Hilly Caffe had

a perfect balance of milk and espresso flavor. Then one day an American businessman named “The

Milk Man” visited Hilly Caffe. The locals eyed the stranger warily and sensed he did not approve of

their coffee ritual, for he always ordered an espresso and an enormous pitcher of steamed milk and

then combined it all in an obscenely large paper cup.

Upon returning home, The Milk Man opened a chain of cafes in order to share his charming Italian

experience with Americans. These cafes had little ambience, no gesticulating Italian men, and no

6-oz cappuccini, however what his cafes did have was very large paper cups filled with a little bit of

espresso and a whole lot of steamed milk. Luckily for the businessman, “bigger is better” is as true in

America as “the Pope is Catholic” is in Italy.

While this man was busy making billions of dollars serving lots of hot milk with a little bit of

espresso another cafe owner was busy obsessing over making tiny, dork espresso shots and cofe

lattes with pretty pictures on them. One day this second man, named “The Temperature Guy,” wrote a

book about dark espresso shots and pretty lattes. The book was coiled Obsessing Over Temperature

Stability. It sold many copies. It is not known whether The Milk Man ever read the book.

Before the book was written, lots of baristi in little cafes across America made big cofe lattes in

an attempt to get rich like The Milk Man. But they couldn’t compete with The Milk Man because they

didn’t have his genius for marketing and real estate. Luckily, The Temperature Guy’s book came along

with the answer to how to make a better latte than The Milk Man’s: the double ristretto.

After reading The Temperature Guy’s book, baristi began using double baskets to make small,

dark shots, and they began grinding each shot to order. Grinding each shot individually required

baristi to use finger-strike dosing, as instructed by The Temperature Guy. Finger-strike dosing involves

dosing the grounds up to, or above, the rim of the basket, and then leveling the dose with a finger.

Baristi who used finger-strike dosing ended up, perhaps inadvertently, using larger doses than the

baskets were designed for.6

Progressive preinfusion. Infusion begins at low pressure while water fills a

spring-loaded preinfusion chamber attached to the group head. Once water has

filled the empty spaces in the group head and preinfusion chamber, the spring is

extended, allowing the pressure applied to the coffee bed to increase gradually.

Flow restriction. A small restrictor, or gicleur, decreases the flow of water to the

group head. This causes a lag between the initial wetting and the applif;ation of full

pressure. Some do not consider this genuine preinfusion, but flow restriction can

have a preinfusion-like effect. Installing a small gicleur is a smart alternative for

machines not designed to offer low-pressure preinfusion. Gicleurs of different sizes

are available through many espresso parts suppliers.

Electronic preinfusion. Pump pressure is cycled on and off either once or several

times during the first couple of seconds of infusion. This type of preinfusion

does not adequately wet the coffee bed and seems to offer no clear benefits. I do not

recommend its use.

Other Considerations

When adding a preinfusion cycle, it is necessary to adjust the grind setting finer to

maintain a given flow rate. Factors such as the group head design, the spray head

pattern, and the amount of space between the dispersion screen and the top of the

Even after adopting The Temperature Guy’s methods, many quality-conscious American baristi

were still not satisfied with the strength of the coffee flavor in their cafe lattes. To make their lattes

stronger they were faced with a dilemma: either use two portafilters for each big latte, or use one

portafilter with an even bigger dose of grounds. Using two portafilters for one beverage was too time

consuming, so these baristi adopted the triple ristretto.

The use of such large doses had many ripple effects on espresso quality and caused baristi

to make adjustments. Larger doses absorb more heat from the brewing water, so baristi began

using higher brewing temperatures. Larger doses offered more hydraulic resistance, so coarser grinds

were used to maintain the traditional (some would say dogmatic) 25-second extraction time. Perhaps

most importantly, because baristi increased dose sizes without increasing shot sizes, they increased

espresso brewing ratios.

The espresso brewing ratio is the ratio of the mass of a dry dose of grounds to the mass of a shot

produced by the grounds. Higher espresso brewing ratios produce shots with lower solids yields; such

shots are typically brighter and more acidic, and often sour or sharp. Shots made with lower espresso

brewing ratios tend to have higher solids yields, mellower flavor profiles, and more bittersweet and

caramel tones.

Recently, a very smart man named Jim wrote a paper 6 in which he discussed the effects of very large

doses on solubles yield and flavor profile.* Immediately all of the geekiest American baristi read Jim’s

paper, and many scratched their heads, wondering what to do with the new information. Ironically, many

of them rediscovered the virtues of making espresso the way the baristi always have at Hilly Caffe.

Meanwhile, the men at Hilly Caffe are still enjoying their small, caramel-sweet espressi and cappuccini.

Once in a while a traveling American barista enters Hilly Caffe, and all the men stop their

arguing and gesticulating to listen to what the American orders. And when the American orders caffe

normale, they nod and smile and return to their arguments.

• The paper referred to solubles yield, not solids yield. Jim has since revised some of his findings, but the bulk of the

paper is still a valuable resource for baristi.

coffee bed all affect the results produced by preinfusion. As with so many of the

parameters of espresso making, experimentation and blind tasting are required to

get the most out of any machine and coffee.

Espresso-Making Techniques in Italy Versus America

In the past two decades, non-Italian baristi have developed new espresso-making

techniques, and many espresso cultures have drifted from the traditional Italian

methods. In this section I will focus on the differences between Italian and American

dosing and temperature standards.

Dosing Standards

In Italy the typical dose is approximately 6.5-7 grams per single (1-oz or 30-ml)

shot and 13-14 grams per double (2-oz or 60-ml) shot. Historically, these parameters,

in conjunction with pregrinding and standard single and double baskets have

produced an accepted range of espresso brewing ratios and brew strengths.

Recently many American baristi have taken to using larger doses, often greater

than 20 grams. Among the more progressive baristi, the typical dose for a single

shot has evolved from a 7-gram Italian-style dose to a 14-gram double ristretto,

to an overdosed (more than 14 grams) double ristretto, and, finally, to a triple ristretto.

These shots are not ristretto in the traditional sense (i.e., very short shots

made from single doses) but are shots of standard volume (1-1ó oz) made from

larger (and larger) doses. These new dosing standards are not universal, but they

are relevant because they are used in many of the most admired cafes. This evolution

of dose sizes was an adaptation to two developments: larger American drink

sizes and the popularity of grinding to order.

Temperature Differences Between Italy and America

I’ve often wondered why so many Italian baristi use dispensing temperatures in the

185°F-195°F range, while many American baristi, especially those considered very

progressive, use 198°F-204 °F. I think one part of the answer is most Italian baristi

use 7-gram doses to yield 1-oz shots, whereas many Americans use 18-21 grams

to yield 1-oz shots. Despite the differences in dispensing water temperatures, both

systems result in similar average extraction temperatures.

Why is that? Because the larger dose used by Americans absorbs more heat

from the brewing water.

To illustrate, here is an interesting thought experiment: If you were to put 7

grams of 8o°F grounds and 30 grams of 190.5°F water (potential inputs of a typical

1-oz Italian “Hilly Caffe” shot) in a preheated container, the mixture’s temperature

would be 181.1 °F. If you then put 21 grams of 8o°F grounds in an identical container

with 38 grams of 203.5°F water (potential inputs of a typical 1-oz American

“The Temperature Guy” shot), that mixture would also measure at 181.1°F. It is

assumed each gram of grounds absorbs 1 gram of water.

The data used in the thought experiment is depicted more clearly in the following

chart:

30 Espr·esso

I

DRY COFFEE/HOT WATER MIXTURE AT EQUILIBRIUM TEMPERATURE

HILLY CAFFE TEMPERATURE GUY

Water mass (excluding waste) (g) 30

Water temperature (OF) 190.5

Dry coffee mass (g) 7

Dry coffee temperature (OF) 80

Dry coffee specific heat 0.4

Approx espresso mass (g) 23

Approx vol/mass ratio 0.04

Approx gross volume (oz) 0.9

Equilibrium temperature (Of) 181.1

How these calculations were made:

Hilly Caffe: 181.1 = (30x 190.5 + (7x80x0.4))-;- (30 + (7×0.4))

Temperature Guy: 181.1 = (38×203.5 + (21x80x0.4)-;-(38 + (2lx0.4))

38

203.5

21

80

0.4

17

0.06

1.0

181.1

A sincere thank you to Andy Schecter for teaching me about specific heat and reworking these

numbers to make them accurate.

Systems for Making Great Straight Shots and Great Milk Drinks

The best shot for straight espresso is not the same as the best shot for a 12-oz cafe

latte. A straight espresso should have moderate brew strength and optimize the

potential flavor profile of the blend used. A shot with too little brew strength will

lack body because brew strength and body are highly correlated; too much brew

strength will interfere with an espresso drinker’s ability to perceive subtler flavors.

The ideal shot for a 12-oz latte needs to have enough mass and brew strength

to balance the volume of the milk. The flavor profile of such a shot is important,

but not nearly as important as the flavor profile of a straight shot because in a latte

much of the espresso’s subtler flavors are blunted by the milk.

To accommodate the needs of both espresso drinkers and latte drinkers, most

quality cafes in the US simply use one large dose size for all shots. This can result in

reasonably good straight shots and lattes, but it is expensive and wasteful and does

not simultaneously optimize shots for lattes and straight espresso.

I recommend two systems that cafes can use to tailor shots to their intended

purposes.

Use two separate grinders: One way to pull two distinctly different types of

espresso shots is to use two different coffees and grinders. Additionally, depending

on the espresso machine, one group head can be dedicated to straight shots, with

its temperature tailored to the coffee being used.

Use different basket sizes and customized dosing and grooming methods:

If a barista uses the traditional Italian dosing standards of 7 grams for a single

and 14 grams for a double, the resulting shots will all have roughly the same brew

strength, flavor, and flow rate. However, if a barista uses finger-strike dosing with

single and double baskets, the dose in the double basket will be less than twice the

Espresso 31

My dosing education (or “how I had to travel to two continents just to

learn how to dose”)

The first time I went to Italy I had been a barista for eight years and was accustomed to

pulling 1-oz to 1 ó-oz shots with triple doses (20 grams) of grounds. Compared to my

own espresso, most shots I had in Italy were sweeter, less acidic, more yellow in color,

and had less body. When I returned home I tried to modify my own espresso to mimic

the flavor profiles I had experienced in Italy, but I never had satisfactory results.

A few years later I worked for Mojo Coffee in Wellington, New Zealand. Mojo

used Italian dosing standards with a lightly roasted (pre-second crack) blend made

up mostly of acidic, washed coffees. I had expected the espresso to be overwhelmingly

bright and acidic but instead it was pleasingly sweet with moderate acidity. It

was clear the difference in dosing was at least somewhat responsible for the mellow

and sweet flavor profile. To test this idea I attempted to pull double ristretti using an

overdosed double basket. (We had no triple baskets, and that was the closest I could

get to the doses used at my old cafe.) The resulting shots were typically sharper and

less sweet than those made with Mojo’s dosing method and espresso brewing ratio.

When I returned to the US and opened my second cafe, I reverted to using 20-

gram doses. I would have liked my own espresso to taste more like the shots I had

made in New Zealand, but I had a dilemma: I could not make a satisfactory 12-oz

or 16-oz latte with a smaller dose because the espresso flavor drowned in the milk.

Given that sales of straight shots were less than 5% of espresso beverage sales, it

was hard to justify compromising the other 95% for the sake of better-tasting straight

espresso. (Please withhold your purist outrage until the end of the chapter.)

size of the dose in the single basket.* This will result in different flow rates (faster

in the double), brew strengths, and flavor profiles.

An alternative system is to use two or three different basket sizes with customized

dosing and grooming systems for each. For instance, at home I have one

grinder, one single basket, and one double basket. I like to use the single basket

to make a mellow, sweet espresso normale with moderate brew strength and the

double basket to make a double ristretto with more body and brew strength for

a cappuccino. If I groom the double basket with a level tool and groom the single

basket with the round lid of my grinder’s dosing chamber, both baskets will yield

1-oz shots of similar mass and flow rate. Moreover, each shot will be of the desired

espresso brewing ratio, flavor, and brew strength for its intended purpose.

Pressure Interruptions During Espresso Brewing

While a shot is being pulled, several events can temporarily decrease pressure.

(These concerns do not apply to lever machines.)

1. Purging or flushing another group

* It will be roughly 1.5 times as much; the exact ratio depends on the coffee, dosing method, and the

type of basket used. The examples described assume all single shots have identical mass and all

double shots have twice the mass of the single shots.

32 Espresso

2. Pulling a shot on another group

3. Engagement of the automatic boiler fill valve

4. Other machines filling, decreasing line pressure to the espresso machine

Such variations in pressure can promote channeling in the original shot and should

be avoided whenever possible, using a few simple strategies.

1. Do not purge a group until all shots on other groups have been completed.

2. To pull two shots, purge both groups and prepare both portafilters before

starting both shots simultaneously.*

3. Rewire your machine to prevent opening of the boiler fill valve while the

pump is engaged.

4. If other machines (brewer, dishwasher, etc.) are competing with the espresso

machine for water pressure, the espresso machine can be protected with

the following setup. In order, from the upstream source to downstream,

install water treatment, pressure bladder tank, pressure restrictor, and

espresso machine. The water treatment is first because the pressure output

of most systems fluctuates. The pressure fluctuations are then absorbed by

the bladder, a balloon that exerts a high, constant downstream pressure

regardless of the pressure upstream ofit (within reason). The high-pressure

output from the bladder is then decreased by the restrictor to the desired

inlet pressure of the espresso machine. The bladder and restrictor combination

should cost about $200.

* Busy baristi will find strategies I and 2 impossible to consistently implement without slowing

service too much. That said, all baristi should make use of these strategies as often as is practical.

Espr·esso 33

Chapter 3

Tl1e Science and Theory of

Percolation a11d Extraction

I researched and wrote this chapter to teach baristi about the dynamics of espresso

percolation. Some will find this section fascinating and satisfying; others will find

it mind numbing. I believe it is w01th the effort to read and understand, especially

because it will provide knowledge that is necessary to diagnose many percolation

and extraction problems.

Percolation Dynamics

The dynamics of espresso percolation are very complicated and not completely understood,

but some useful models have been developed to describe what is known

of the process. These models will be easier to visualize if we first discuss and observe

the more familiar interaction of grounds, gases, and water in a filter during

drip coffee brewing. This can be done with a manual pourover or any drip brewer

that allows the grounds to be viewed during brewing.

35

The Dynamics of Percolation and Extrnction: Drip Coffee

Phase t: wetting Water is showered onto the coffee bed, wetting the grounds

and causing them to rapidly release CO2

The emitted CO2 repels the water and

causes turbulence, inhibiting both the wetting of the grounds and the flow of liquid

through the coffee bed. The turbulence is evidenced by the layer of foam covering

the spent grounds after brewing.

Water always follows the path(s) of least resistance through the grounds and

therefore flows down the coffee bed somewhat erratically. The water both removes

solids from the grounds and gets absorbed by the grounds, causing the unabsorbed

liquid to become progressively more concentrated as it descends the coffee bed. The

grounds swell as they absorb liquid.

Phase 2: extraction The coffee exiting the bottom of the filter is initially viscous

and concentrated. As extraction proceeds, the exiting liquid becomes more dilute

because there is less readily extractable material available in the coffee bed.

Extraction occurs in two phases. In the first phase, solids are washed off the

surfaces of the grounds. In the second phase, solids are transferred from the inner

coffee particles to the water by inner-particle diffusion, 8 the movement from an

area of higher concentration to an area of lower concentration.

Diffusion occurs in a series of steps. First, water contacts the coffee particles and

drives out gases. Second, water enters the pores of the particles, the particles swell,

and solids within the particles dissolve. Third, the dissolved solids diffuse to the

particle surfaces and then into the surrounding solution. 8

During brewing, water is continually added to the top of the system, diluting the

turbulent pool of liquid, grounds, and gases. This dilute liquid near the top of the

coffee bed effects rapid diffusion from the upper layers of grounds due to a steep

concentration gradient (the difference between the concentration of coffee solids

within the grounds and within the surrounding liquid). Extraction is slower in the

lower coffee bed because the liquid there is more concentrated with solids, reducing

the concentration gradient. The result is uneven extraction, with more solids

removed from the upper than the lower coffee bed.*

The Dynamics of Percolation and Extrnction: Espresso

The dynamics of espresso and drip percolation are similar, although espresso

extraction is accomplished primarily by washing, with little or no role played by

diffusion. The models developed to describe espresso percolation are not comprehensive,

but they have shown validity by successfully predicting the results of realworld

experiments. 1

2

,:Hs The following is derived from a combination of published

research and the current knowledge base of the specialty coffee industry.

Phase t: wetting In the first phase, water fills the headspace of the extraction

chamber, driving out gases 2 and wetting the grounds. The grounds absorb water,

while simultaneously the water picks up solids from the grounds. The absorption of

water causes the particles to swell9 and the coffee bed to decrease in porosity. 2

* Extraction from the upper and lower coffee bed can be made more equal by using a cone-shaped,

rather than cylindrical, basket. (See the discussion of basket shape later in this chapter.)

The Science and Theory of Percolation and Extmction

As the water flows through the bed it erodes solids from the grounds, transports

the solids, and deposits some of them lower in the bed. 0 This causes the solids content

of the lower coffee bed to increase* during the wetting phase.”(,

The coffee bed is exceptionally vulnerable to channeling during the wetting

phase. The lack of cohesion of the dry particles, reorganization of the coffee bed

due to particle migration and swelling, high rates of solids removal, and, in some

machines, an abrupt increase in pressure during this phase all increase the likelihood

of channels forming.

By the end of the wetting phase the coffee bed has been radically transformed:

it has lost porosity, swelled, and absorbed heat from the brewing water, gases have

been driven out, solids have been transferred from the upper to the lower coffee

bed, preferential paths have been created, and channels might have formed.

Phase 2: pressure increase A pressure gradient causes the water to flow from

the area of high pressure above the coffee bed to the area oflow pressure at the outlet

of the filter basket. According to Darcy’s Law of fluid dynamics, as the applied

pressure increases, the flow of water through the coffee bed will increase. However,

empirical evidence in published research’ apparently contradicts Darcy’s Law in

two ways. In this study:

1. As pressure increased during extraction, flow rate initially increased, then

peaked and decreased, leveling off asymptotically to a nearly constant rate.

2. In a sample of several shots pulled with various applied pressures, shots

pulled with higher pressure had higher flow rates, but only up to a certain

pressure. Beyond that pressure the average flow rate either remained

constant or decreased. What this means in plain English is, if you were to

increase your espresso machine’s pump pressure from 9 bar to 12 bar, the

flow rate of your shots might decrease.

Several possible reasons explain why the flow rate might decrease during the phase

of increasing pressure. First, particle swelling during this phase due to the wetting

of any remaining dry coffee decreases the porosity of the bed and causes an increase

in hydraulic resistance. Second, the increase in pressure causes the coffee bed to

compact, ,:i increasing hydraulic resistance. Finally, the increased pressure “favors

displacement of coffee bed particles (i.e., fines migration) and a gradual compaction

of the coffee bed as a reaction.””

Phase 3: extraction Researchers offer conflicting opinions regarding the relative

contributions of washing and diffusion to extraction in different forms of brewing.

One researcher who compiled data concluded the dominant mechanism of extraction

was the washing of solids from the outer surfaces of coffee particles. c- Another

analyzed the same data and concluded that 85%-90% of extraction in the first minute

(and presumably 100% thereafter) was due to inner-particle diffusion.’ 8 If this

second researcher is correct, diffusion could play a role in espresso extraction.

•· It is not known how much of the reported increase is due to deposited solids and how much is

attributable to solids being transferred through the lower bed in the extracting liquid when the

process was interrupted and measurements were taken.

The Science and Theory c>(Percolcztion and Extraction 37

THE DYNAMICS OF ESPRESSO PERCOLATION AND EXTRACTION

DRY

T=-10 seconds

FULL PRESSURE & FIRST EXTRACT

T=0 seconds

MID-EXTRACTION

T=lS seconds

LOW PRESSURE WETTING

T=-1 second

BEGINNING OF EXTRACTION

T=S seconds

LATE EXTRACTION

T=25 seconds

The color of the grounds (represented by the stocked rectangles) in the first frame is deep red,

indicating they are concentrated with coffee solids. The lighter reds in loter frames represent

lower solids concentrations.

T = -10 seconds: The dry grounds ;ust before the pump is engaged. The grounds ore pocked

with solids, and fines ore scattered throughout the coffee bed.

T = -1 second: The coffee bed near the end of preinfusion. The water has percolated through

almost all of the coffee bed but extraction hos not yet begun. The grounds hove absorbed

waler, swelling the coffee bed. A channel, represented by the yellow line, has formed through

the middle of the coffee bed. The upper layers of the coffee bed have lost solids, while the

lower coffee bed hos gained solids. Fines have begun lo migrate down the coffee bed.

T = 0 seconds: The first extract appears. The first extract appears al the outlet of the channel.

Fines and solids hove concentrated in the lower layers of the coffee bed. The coffee bed contracts

as pressure increases.

T = 5 seconds: Early extraction. Solids and fines are rapidly removed from the coffee bed. The

coffee bed is further compressed as full pump pressure is applied.

T = 15 seconds: Mid-extraction. The coffee bed shrinks as it loses mass. The upper layers of

the bed are almost depleted of extractable solids. The bulk of fines and solids ore concentrated

in the lowest layers of the bed.

T = 25 seconds: Final moments of extraction: The upper layers of the bed ore completely empty

of extractable solids. The coffee bed has lost about 20% of its original dry moss.

The Sci<‘nce and Theory of Percolation and .Extractio11

According to the research done with large percolator columns, diffusion does

not occur until coffee particles are:

1. “Satisfied with bound water.” Coffee particles can hold up to about 15% of

their dry weight as bound water.'”

2. Saturated with free extracting liquid.-

3. Free of gases.7

The typical espresso extraction time is probably too short for all three preconditions

of diffusion to be met. Therefore, it is likely that espresso extraction is accomplished

entirely by the washing of solids from the outer surfaces of coffee particles,

as well as by the emulsification* of oils.<1D iffusion plays little, if any role.

Flow P,-ogressio11

The initial extract from the flow of a well-prepared shot should be viscous and

dark.+ As the flow progresses the extract becomes more dilute and the color gradually

lightens, eventually turning yellow. Cutting off the flow when it yellows, or

* The emulsification of oils seems to be enabled by the pressure of espresso brewing. lt is arguable

that the emulsion is the aspect of an espresso most responsible for differentiating it from a very

concentrated cup of coffee.

* The color of the extract is believed to be darker when it has a higher concentration of caramelized

solids or a lower concentration of CO,, though there may be other factors that influence color.

The Science and Theory of Pe1·colatio11a nd Extraction 39

“blondes,” limits dilution of brew strength but has less effect on flavor than is commonly

believed, because the extract has a very low concentration of flavoring material

in the later stages of extraction.

Solids removal from the upper layers of the coffee bed is rapid during wetting

and early extraction.” This is due to the presence of high temperatures, the relative

ease of particle migration during the wetting phase, and the presence of a steep

concentration gradient.

In the lower layers solids content initially increases during wetting and then stabilizes

during early extraction” as the lower coffee bed loses smaller, fast-dissolving

solids and simultaneously gains deposited fines. The net result is that the upper layers

of the coffee bed contribute a much greater percentage of solids to the cup than

do the lower layers. 5•

6

Fines

Migration of fines, or ultra-fine cell wall fragments, is the “x factor” of espresso

percolation. Though I am not aware of any direct measurement quantifying fines

migration, there is quite a bit of indirect evidence of its existence in published research

‘·6•7•9 and in the predictive ability of mathematical models* that are based on

the assumption that fines migrate and form a compact layer at the bottom of the

coffee bed. 1.4.s

Formation of a significant compact layer can disrupt even percolation by obstructing

holes on the bottom of the filter basket. Formation of a compact layer can

harm espresso quality by causing several problems.

1. An unintended reduction in flow rate. Any barista who has experienced a

decrease in flow rate during extraction was probably witnessing the result

of increased hydraulic resistance caused by growth of the compact layer.

2. Uneven extraction patterns and channeling.

3. Reduction in body, if too many fines settle in the layer instead of contributing

solids (both soluble and insoluble) to the cup.

The Effects of Fines on Espresso Quality

Beyond the formation of a compact layer, fines have positive and negative effects

on espresso quality. To gain insight into the effects of fines, I used a 90-micron

sieve to remove a large quantity, perhaps the majority, of fines from the grounds

before dosing. =I= The first apparent effect of removing the fines was a faster flow rate,

* Some of the mathematical models referred to have been used to create espresso percolation simulations

able to accommodate numerous input variables. Real-world experiments have validated

the predictions of these models for such values as percentage of a coffee bed wetted during preinfusion,

quantities of solids remaining in different layers of a coffee bed after extraction, and

percolation flow rates.

* I did not quantify the proportion of fines I removed; I simply shook the sieve for about a minute,

at which point no more fines were passing through the sieve.

40 The Science and Theory c~f Percolation and Extraction

which indicated that fines provide flow resistance. After adjusting the grind finer to

rebalance the flow rate, I pulled several shots with the sieved grounds. Compared

to “normal” shots from the same beans, the mostly fines-free shots had less body

and less bitterness.

Because the presence of fines contributes positively (more body) and negatively

(more bitterness) to espresso, the best espresso should result from finding the ideal

proportion of fines for a given dose size and by limiting the migration of those fines

to prevent formation of a compact layer. There is no practical way to measure fines

production or migration, however, there are methods of decreasing fines production

and migration.

Limiting Fines Production

Production of fines is inevitable during grinding due to the brittleness of roasted

beans. For a given grind setting, there are four ways to reduce the quantity of fines

produced: use sharper burrs, 11 use a lighter roast,7 use slower grinding speeds,7 or

use beans with higher moisture content.”

Limiting Fines Migration

A barista can monitor fines migration indirectly in two ways: by observing the uniformity

of extract flow and color with a bottomless portafilter and by inspecting

the filter basket holes after knocking out spent grounds. (Color should not vary too

much from area to area, and the filter basket holes should be clear.) Based on these

observations a barista can decide whether fines migration is excessive.

The most effective way to reduce fines migration is by using low-pressure preinfusion.

Fines migration is also decreased by use of a finer grind. A finer grind

shrinks migration pathways by decreasing the space between grounds and allowing

more compaction of the coffee bed. 7 Of course, simply making the grind finer will

result in a slower flow rate, but a finer grind used in conjunction with a smaller dose

or a wider basket can balance the flow rate.

Basket Shape and Extraction

A standard single basket is shaped like a truncated cone, while a standard double

basket is cylindrical, or nearly so. Does basket shape affect extraction quality? The

answer is a qualified yes.

Earlier in this chapter it was noted that the upper layers of the coffee bed yield

more solids than do the lower layers during extraction.s-6 Such uneven extraction is

detrimental to flavor and brew strength: the upper layers overextract, yielding bitterness

and astringency, and the lower layers underextract, resulting in less sweetness,

less brew strength, and perhaps some underdeveloped flavors.

The use of cylindrical baskets exacerbates this uneven extraction, whereas using

truncated-cone baskets can balance some or all of it. To explain, consider a hypothetical

set of well-prepared extractions, one in a cylindrical basket, and the other

in a truncated-cone basket. For the moment let’s assume fines do not migrate and

The Science and Theory of Percolation and Extraction 41

FLOW THROUGH SINGLE AND DOUBLE BASKETS

Single Basket

Double Basket

. II

….__

no significant channels form in either extraction. Imagine you can see inside the

coffee beds during the extractions. In your mind’s eye cut each bed into a series of

thin horizontal layers, or cross sections. (Visualize the layers as a stack of discs.)

In a cylindrical double basket the volume ofliquid flowing through each layer is

equal. (Let’s ignore the effect of water absorption for the moment.*) Also, the area

of each layer is identical. Therefore the volume of liquid flow per unit area is the

same in all layers.

In a truncated-cone basket the volume of liquid flowing through each layer is

also equal. However, the upper layers have larger areas, and the liquid encounters

layers of less and less area as it descends the coffee bed. Therefore, during extraction

the volume of liquid flow per unit area increases as the liquid descends. (Think

of it as a road merging from two lanes into one; the same volume of cars flows

down the road before and after the merge, but the volume per lane doubles after

the merge.)

In a single basket, the greater flow per unit area in the lower layers results in

higher extraction yield from those layers. Therefore, in these hypothetical extractions,

the shape of the single basket provides a more uniform extraction.

* In real life, grounds absorb water. This makes calculating the flow through each layer complicated,

but it doesn’t change the fact that there is greater liquid flow, and hence extraction, per unit area

in the lower layers of a truncated-cone basket than in the lower layers of a cylindrical basket.

42 The Science and Theory of Percolation and Extraction

The same dynamic applies to drip coffee baskets; using a cone-shaped basket will

result in more uniform extraction from the coffee bed. Consumer drip brewers with

cone-shaped baskets are readily available. However, I know of no commercial drip

brewers that come with cone-shaped baskets. With commercial machines that offer

a variety of compatible baskets, it is best to use the most tapered basket available.

Espresso Brewing Ratios and Standards

What is a ristretto? A normale? A lungo?

Whereas there is a semblance of standards in Italy, in the rest of the world

espresso is made with a great variety of doses and shot sizes. Consequently, those

three terms have come to mean very different things to different baristi.

It is understood that at a given cafe a normale is a standard shot, a ristretto is

made with the same dose but less water, and a lungo is made with the same dose but

more water. Therefore the three terms refer loosely to espresso brewing ratios.*

Traditionally, baristi have measured shot size by volume, with 1 oz, or 30 ml,

being the standard Italian normale. This presents a complication: because the crema

volume of different shots can vary tremendously, the amount of liquid espresso in

two shots of the same volume can also vary quite a bit. Any barista who has watched

several shots rest for a few minutes can attest to the fact that the amount of liquid

remaining after the crema has dissipated can be very inconsistent.

Crema volume is increased by using fresher beans, grinding immediately before

pulling a shot, adding robusta, using a bottomless portafilter, and other factors.

The proper way to compare espresso brewing ratios and shot “sizes” is to weigh

doses and shots. During service in a cafe it is impractical to weigh shots as they

extract; I do not propose baristi weigh all their shots, but I think they should weigh

shots intermittently to improve consistency. Weighing shots also allows baristi

to communicate more effectively when discussing shot doses, sizes, and espresso

brewing ratios.

The concept of espresso brewing ratios based on shot mass instead of volume is

the brainchild of my friend Andy Schecter, a brilliant amateur coffee scientist from

Rochester, New York.:J:

It is interesting to note that a barista who pulls shots using a machine’s programmable

volumetric buttons will achieve a far more consistent espresso brewing

ratio than a barista stopping shots by sight. Shots produced with the programmable

buttons can vary by volume due to differences in crema quantity, but they will in

fact be of reasonably consistent mass.

” The term brewing ratio is traditionally used in reference to drip coffee brewing; it is the ratio of

dry grounds to brewing water used to make a coffee. In espresso making it is difficult to measure

the quantity of water used due to the high and variable proportion of the brewing water absorbed

by the grounds. Therefore it is practical, if a bit of a misnomer, to define espresso brewing ratio as

the ratio of the mass dry grounds to the mass of the shot.

* Andy’s discussion of these ideas, as well as the original publication of the following chart, appear at:

http://www.home-barista.com/forums/brewing-ratios-for-espresso-beverages-t24o2.html.

The Science and Theory l~f Percolation and Extrnction 43

How should baristi use this information about shot mass and espresso brewing

ratios? First, I think baristi should weigh a few shots per day to help maintain consistency.

Second, when discussing extractions, roasters and seasoned baristi should

include information about shot mass, just as they do about dose size and water

temperatures. Third, baristi should experiment with using the programmable volumetric

buttons, with the caveat that shots still need to be monitored for flow rate

and channeling.

BREWING RATIOS

FOR ESPRESSO

COFFEE

SINGLE

RISTRETTO DOUBLE

TRIPLE

REGULAR SINGLE

ESPRESSO DOUBLE

NORMALE TRIPLE

SINGLE

LUNGO DOUBLE

TRIPLE

SINGLE

CAFE CREMA DOUBLE

TRIPLE

SCAA

DRIP COFFEE

STANDARD

GROSS

DRY COFFEE BEVERAGE BREWING RATIO VOLUME

(g) (g) (DRY/LIQUID) INCL. CREMA

(oz)

LOW MED HIGH SMALL MED LARGE LOW HIGH TYPICAL LOW* HIGH**

7 7 0.3 0.6

16 16 60% 140% 100% 0.7 1.3

21 21 0.9 1.7

7 14 0.6 1.1

16 32 40% 60% 50% 1.3 2.6

21 42 1.9 3.4

7 21 0.8 1.5

16 48 27% 40% 33% 1.9 3.3

21 63 2.5 4.4

7 50 1.8 3.0

16 114 12% 16% 14% 4.0 6.9

21 150 5.3 9.0

55 1000 5% 6% 5.5%

*OLDER BEANS; SPOUTED PF; 100% ARABICA; LEVER MACHINE *’FRESH BEANS; NAKEO PF; USE OF ROBUSTA; PUMP@ 9 BAR

In this chart Andy Schecter defines ristretto, normale, and lungo using espresso brewing ratios.

Not all baristi will agree with Andy’s definitions, but his proposed standards reflect common

practices in Italy, and his definitions happen to be eloquently simple and easy to remember.

To translate, Andy’s typical ristretto is defined as having mass equal to the dry grounds used

to make it. The weight of a typical normale, or “regular espresso,” is twice the weight of the

dry grounds used, and a typical lungo is three times the weight of the dry grounds used. Cafe

crema is simply a very long pull of espresso.

44 The Science and Theory of Percolation and Extraction

Chapter 4

l\1ilk

Milk Steaming

Milk is the primary ingredient by volume in most espresso beverages. As such, its

preparation deserves the same care and attention given to espresso extraction.

Much like choosing a coffee roaster, choosing a milk supplier should be based

on quality and blind taste testing. Milk should be sampled both cold and frothed

and with and without espresso.

Baristi should be aware that the quality of milk from any supplier fluctuates

throughout the year due to changes in the weather and the content of the dairy

cows’ diets. Some years I have had to switch suppliers seasonally, since one supplier’s

milk was better in the winter and another supplier’s was better in the summer.

45

Milk Steaming Goals

The following should be the basic goals of any barista when steaming milk.

• Pour only as much milk as you will need for the current drink(s).

• Create a tight micro-bubble structure when aerating milk; the surface should

be glassy and have no visible bubbles.

• Heat the milk to a final temperature of 150°F-160°F.

• Plan ahead so milk steaming and espresso extraction are completed at about

the same time.

• Serve drinks before they separate!

Milk Separation

The mouthfeel of a cappuccino or cafe latte before the milk has separated is far superior

to the mouthfeel of the same drink a minute or two later. The sin of allowing

a drink to sit and separate before it is consumed is analogous to allowing a shot of

espresso to age before it has been drunk. In each case the beverage is unstable and

its quality declines if it is not consumed in a timely manner. While there is no guarantee

a customer will drink a fresh beverage immediately after it is served, it should

be the barista’s goal to offer every beverage in its ideal form.

There are three steps to serving a milk-based beverage with exceptionally creamy

and long-lasting texture.

1. Steaming. Steamed milk must have a tight micro-bubble structure. Creating

visible bubbles, overheating, and overstretching while steaming can all

degrade the potential texture of a beverage.

2. Pouring. Pouring with the proper flow and skillfully using “the spoon method”

each help delay separation.

3. Serving. Present beverages as soon as they are made.

How to Steam Milk

Use the smallest pitcher that can comfortably accommodate the amount of milk

needed for the beverage(s) to be made. A good rule of thumb is the pitcher should

be about 1/3-ó full before steaming.

1. Puff the steam wand into a moist rag or the drip tray to purge the wand of

any condensed water.

2. Set the steam wand tip just below the surface of the milk, near the center.

The steam wand should be roughly 10°-30° from vertical.

3. Open the steam wand to full, or nearly full, pressure, depending on the

quantity of milk to be steamed. When steaming very small amounts of milk,

such as for a macchiato, less pressure is required.

4. Immediately begin the stretching, or frothing, phase and complete it before

the milk reaches 100°F. Once milk is heated above 100°F, it becomes more

difficult to produce quality froth.

5. While stretching, keep the steam tip just below the surface of the milk and

carefully aerate the milk without forming any visible bubbles. The aerating

should make a consistent, subtle sucking noise.

6. When the desired stretch is achieved, raise the pitcher to sink the steam

Milk

wand deeper in the milk. Position the wand so the milk is kept rolling until

it approaches your desired temperature.

7. Turn off the steam wand, remove the pitcher, wipe the wand with a damp

rag, and carefully purge the wand into the rag.

Please note: With some steam wand tips or very high boiler pressure, aerating with

the tip at the surface of the milk will quickly lead to over-frothing. In such cases the

barista can aerate with the steam tip deeper in the milk, steam with partial pressure,

or lower the pressurestat setting.

Milk Textu,-es of Different Beverages

I would like to propose some beverage recipes simply for the sake of this discussion.

All beverages presented here will be prepared in classic, [talian-style, 6-oz to 8-oz

wide-mouthed ceramic cups, with a base of 1-1ó oz of espresso.

Cappuccino: Made with very aerated milk. The froth quantity should be such

that if the beverage is allowed to fully separate, and then the froth is pushed

back with a spoon, the froth will be about ó inch deep. (This is an estimate

and will vary based on the diameter of the mouth of the cup.)

Cappuccino froth should be deep and plush. When it is

pushed aside there should be no visible, separate layer of

non-oeroted milk.

Cafe latte: Made with moderately aerated milk. The depth of the froth after

separation should be about . inch.

Milk 47

A cofe latte 2 minutes ofter it was mode. At this point the

milk hos fully separated.

Flat white: Made with minimally aerated milk. There should be only a skin of

froth on top.

Grooming Milk

No barista will aerate milk pe1fectly for every drink. If milk is under-aerated, little

can be done other than to quickly steam a new pitcher. If the milk is over-aerated,

however, the milk can be groomed to achieve the desired texture.

To determine whether milk has been properly aerated, set the pitcher of steamed

milk on the counter and spin the milk. Spinning consists of moving the pitcher in

tight circles without changing its orientation. Spin the pitcher fast enough to whip

the milk around the walls of the pitcher in a controlled manner, but slowly enough

to prevent bubbles from forming. The more aerated the milk is, the more viscous,

or “sticky,” it will be when spun.

If it is too aerated, the very frothy top layers of milk should be removed by

grooming. To groom, skim the surface of the milk with a large spoon and remove

some of the surface froth. Skimming should be done with the bowl of the spoon

partially visible, to avoid scooping deeper milk. The smface should be skimmed

as evenly as possible. After grooming, spin the milk to evaluate its texture, and if

necessary, repeat grooming and spinning. Continue alternating grooming and spinning

until the desired milk texture is achieved. The entire grooming process should

be completed in no more than a few seconds.

Spinning can also be used to delay milk separation. Effective spinning is rapid

enough to keep the surface of the milk glassy but not so rapid that new bubbles

form or milk spills.

Milk

Coordination of Extraction and Steaming

Milk steaming and espresso extraction should be coordinated so steaming is completed

a few seconds before extraction is finished. Espresso is ready to be combined

with milk as soon as extraction is completed, but milk requires about 5 seconds to

settle after the steam wand is turned off. Any necessary grooming should be done

after this short rest.

If extraction is still not complete after the milk has been groomed, the milk

should be spun to delay separation. Spinning should not be used as a crutch, however;

even when milk is spun, its texture degrades with time, so milk should always

be poured within 30 seconds of steaming.

Milk Pouring

I will discuss two milk-pouring methods: free-pouring and the spoon method. Each

has advantages and disadvantages, and each has its place in a barista’s repertoire.

Free-Pouring

Free-pouring is the dominant s:vstem in use today. It involves steaming milk in a

spouted pitcher and then simply pouring the textured milk into the espresso. The

milk should be poured at a controlled rate slow enough to keep the crema intact but

fast enough to prevent the milk from separating in the pitcher. The spouted pitcher

is commonly used because it allows the milk flow to be directed, making it easier to

create latte art.

Milk 49

Begin by pouring the milk

into the center of the creme.

Pour quickly enough to

prevent separation in the

pitcher but slowly enough to

keep the creme intact.

Continue rocking the pitcher

to create a zigzag pattern. It

is critical to resist the urge to

raise the pitcher away from

the surface of the beverage.

It may be counterintuitive,

but keep the pitcher as low

as possible while pouring

and constantly accelerate

the tipping of the pitcher to

maintain the flow rate.

so

Maintain a consistent,

moderate flow rate throughout

the entire pour. To do

this, you must accelerate the

tipping motion of the pitcher

as the amount of milk in the

pitcher decreases.

Back the pitcher toward the

edge of the cup while zig•

zagging. Once you reach

the edge of the cup lift the

pitcher a couple of inches

and drizzle a small stream

of milk back across the centerline

of the zigzags.

Rock the pitcher bock and

forth once the white cloud

appears.

Eccol

Milk

How to Pour Latte Art

To pour latte art you must have a fresh shot of espresso with a reasonable amount

of crema and properly textured steamed milk. The milk should look creamy and

glassy, with no visible bubbles.

The most common mistakes beginners make are pouring the milk too slowly

and lifting the pitcher away from the surface of the beverage while pouring. Pouring

milk too slowly can cause it to separate in the pitcher, causing less-aerated milk to

pour into the beverage and more-aerated milk to remain in the pitcher. This makes

pouring latte art difficult and also results in an under-aerated beverage. Raising

the pitcher away from the surface of the beverage causes the milk to dive under the

crema rather than resting on top of the crema and forming a design.

Raising the pitcher while pouring prevents the milk from resting on the crema because

the flow of the milk is accelerated by gravity. Raising the pitcher is analogous to diving

from a high board: just as the milk dives to the bottom of the cup and hardly disturbs

the crema, the diver cuts through the surface of the water with hardly a ripple and

submerges deeply. On the other hand, pouring with the spout of the pitcher kept very

close to the surface of the beverage is analogous to diving from the edge of a pool: