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Copyright © 2015 by Rob Hoos
All rights reserved. This book or any portion thereof may not be reproduced or
used in any manner whatsoever without the express written permission of the
publisher except for the use of brief quotations.
Written and Researched in Portland, OR
Printed in the United States of America
ISBN Number: 978-0-692-41770-6
Library of Congress Control Number: 2015906973
Rob Hoos
[email protected]
To Laura and Abigail: The loves of my life, two women who make every day a
To John and Meribeth Hoos: My parents who are the reason I am the person I
To Kevin Hoos: My brother who I respect and admire more than I can tell him (I
don’t want it to go to his head).
To William Schaefer: An intensely close friend who has been with me through
thick and thin, and who was a sounding board to me throughout this process.
To Zach Lemmon: One of my oldest friends, without whom I may have never
gotten into coffee.
To Augusto Carvahlo Dias Carneiro, for not only bringing me to Portland, but
for encouraging me during the course of my writing of the book. He is basically
the best boss ever.
Photo by Connie Blumhardt
To be honest, nothing makes me as uncomfortable as telling people about
myself, especially when the purpose of disclosing that information is to impress
them. That being said, seeing as I am neither famous, nor infamous; nor do I
work for a national or internationally known coffee roaster, I will divulge a few
reasons regarding my experiences, thoughts, and opinions that may be
As a consultant:
I specialize in flavor profile matching, especially when switching
roasting equipment manufacturers.
To my credit, I have been able to apply theories discussed in this
handbook to match flavors so closely that the roasting teams I have
worked with haven’t been able to differentiate between the coffees
they roasted, and the coffees I roasted. (On different roaster
manufacturers as well).
I have successfully worked with a wide variety of clientele from both
the “second and third wave” in coffee. Some of which are household
names, and others are well known regionally.
I am very involved with the Specialty Coffee Association of America
(SCAA) and the Roaster’s Guild of America (RG), specifically in industry
Instructor Development Program Certificate Holder
Specialized Lead Instructor for Roasting Certificate Holder
Subject Matter Expert on Roasting for SCAA/RG
Member of the Roaster’s Guild Certificate Committee
Content contributor and developer for Roaster’s Guild Level 2 courses
at the SCAA Leadership Summit
Instructor for Roaster’s Guild Level 1 Certificate Program in Beijing,
Certificate Holder Roaster’s Guild Level 1 & 2
Lead Instructor and Station Instructor for the Specialty Coffee
Association of America
I have a wide range of experience within the coffee industry:
Barista trainer
Production / Packaging
Green Buyer
Lead Educator
Production Roaster
Lead Roaster
Director of Coffee
Independent Consultant
I am a professional within the coffee industry:
Currently I am the Director of Coffee for Nossa Familia Coffee in
Portland, OR.
In the last 3 years, I have logged over 7,500 production roasts alone. If
they average 12 mins. per roast, then that is 1,500 hours of my life, or
62.5 days (not counting sample roasting, profile development, and
roasting for fun)
I’ve been interested in coffee since 2001
I’ve been working in coffee since 2006
I’ve been roasting coffee since 2009
Anyhow, I hope that is enough about me. Bottom line for me is not related to my
credentials; rather to my experience that everyone that I know who has applied
these basic approaches to modulating the flavor profile of their coffee have
reported back to me that it works. Friends and colleagues of mine who are also
professional roasters buy in, and that is enough to keep me from thinking that I
am either insane, an egomaniac, or a fool.
In this handbook, I provide a lot of linkage with what sort of science I believe to
be going on during roasting that causes the changes in my experience of the
flavor profile. These are, to a certain extent, my opinions. I am not a scientist by
trade. I do not (unfortunately) have a gas chromatograph or a mass spectrometer
at my house, or in my lab at work. The truth is, whatever science I state has
come to me through a lot of reading, thinking, and drawing of logical
conclusions (though I think it to be reasonable and well thought out). I am
looking , forward to testing these items out and plan to adjust my opinion along
the way.
This project started before I moved to Portland in late 2011.
It is ongoing...
Please read the book in order the first time, it will help you understand things
One of the things that got me interested in coffee in the first place was an intense
fascination with the multitude of possibilities and nuanced dissimilarities in the
flavor profiles of coffee. During my time as a barista, I had learned how I could
modulate those flavors within the coffee through altering the extraction. Part of
what helped me understand how to do this was the vast amount of information
on the Internet and bookshelf about that role and the effects of different
extraction parameters on the final taste of the cup.
When I started working as a coffee roaster, a whole new world opened up to me.
As I excitedly dove into roasting, thinking that here I would be able to take
control of the flavor profile of coffee to the next level, I quickly realized that I
was diving into a sort of vacuum. The roasting community seemed much less
accessible to me as a beginner (and as a roaster in the Midwest). I assumed that
people had the information I sought (essentially, how to change the way that
coffee tasted by changing the roast profile) and that, for whatever reason,
I was simply unable to access it. So I decided to purchase my own 1-kilo roaster
and began to figure out how to modulate the flavor profile by altering my roast
profile. I read every book, website and scientific article I could get my hands on,
and then began to develop theories based on all of my experiences roasting and
cupping up to that moment. I then began to use basic means of scientific method:
experimentation, control of variables, observation, and repetition
My propensity for reading, experimentation, and became more involved in the
specialty coffee industry. Through working with various coffee industry groups
(SCAA, Roaster’s Guild, etc.) and consulting, I came to realize that the void in
information about modulating flavor through profile manipulation was not
imagined, nor were people just “holding out” on me. For the most part, it seems
as if no one had (or has) presented information most relevant to the end goal of
cup quality/characteristics. It is into this void that I hope to shout with this
I have been as precise, objective and analytical as I can be with my current
equipment. Readers should be able to take my experiments and reproduce them
to test my theories and paradigms. I have been working with this approach for
the past three years and have found it to be true regardless of roaster
manufacturer, batch size, origin, altitude, etc. I hope that these standards can
help you as much as they have helped me. Additionally, with something as
complex as coffee, I recognize that the nuance, and thus the conversation, is
never over. That is why I will be hosting a blog and ongoing discussion
concerning the ideas I have presented in this handbook
( Ideally, this will help the community of
professional and home coffee roasters continue to advance our understanding of
our passion and profession.
Manifesto: “a public declaration of intentions, opinions, objectives, or motives,
as‘ one issued by a government, sovereign, or organization.”1
I appreciate the definition of a manifesto. I have always been a person who
desires to be completely direct and up-front. For that reason, as I begin the
writing of this manifesto, this presentation of my beliefs and opinions about
coffee roasting, I have decided to just lay everything out on the line. Below are
the honest reasons why I am writing this handbook:
1. This handbook is meant to document, and clarify through the act of writing,
exactly how I currently understand and approach coffee roasting, especially
with respect to the flavor development of coffee during roasting (and how
changing the profile can affect the flavor of the coffee).
2. Coffee is my passion, hobby, and profession. When it comes right down to
it, I am taking the time to put all of this into writing because coffee is
something that I am intensely passionate about and in which I am heavily
3. I worked a long time to develop this specific approach to coffee roasting
and flavor development and would like to contribution to the industry.
4. Finally, I am hoping that after reading this, some of you will approach me
and ask me for some help in the form of consulting. I do not have a big
name or a reputation in the industry. That is okay, but in order to do the
work I really enjoy, I have to put myself out there like this.
I have chosen to write this handbook more informally. I have some internal
conflict over the style I should use to present this information because my
greatest desire is to present an incredible, bullet-proof scientific article/ book.
However, between work, consulting, and family life, “ain’t nobody got time for
that.” Although I am employing the scientific method to the best of my ability in
the experimentation and observation that has led me to the conclusions I hold so
dear, due to time and resources I am not able to compose the formal scientific
paper that I plan to write in the future (hopefully with the help of someone with
access to a mad-scientist lab). This publication then, is a preamble to the larger,
professional, robustly scientific publication that will come at a later date. In
addition, this publication will work to bring my ideas on coffee flavor
development to people in a way that may be easier to apply to their day-to-day
This handbook is a manifesto because I hope to do a few things with it. I hope to
challenge the status quo within the coffee industry that treats the act of coffee
roasting as an art form, lacks expectations for consistency, and treats the creation
of flavor compounds within coffee as some sort of black magic. Additionally, I
want to present my perspective on coffee roasting, flavor development, and
consistency. The act of writing is an invitation for the reader to enter my brain,
and I am sorry for the mess.
manifesto. Unabridged.
Random House, Inc.
(accessed: October 17, 2014)
In defining the unique aspects of my approach to coffee roasting, I am outlining
a philosophy or paradigm more than anything else. My philosophy begins with
the idea that coffee roasting is a definable, understandable process for which a
unified theory can be created. This is not to say that every specific detail that
plays a part in coffee flavor development can be perfectly predicted and
understood. Rather, there exist trends of flavor development common to all
coffees and by understanding these trends, informed and intelligent decisions can
be made. As Oregon roaster and inventor Michael Sivetz stated in Coffee
Technology, “Although green coffees vary in chemical and physical properties,
the chemical and physical changes they undergo during roasting are similar even
though they vary in degree.”2 Thus, the bulk of my time and effort has focused
on learning how to appropriately deconstruct the roast curve and understand its
components, and then — through application of scientific method — manipulate
the roast curve to produce the desired changes to the flavor of the coffee.
There are a number of points of the roasting curve that I find to be incredibly
important — specifically for coffee flavor development — including the
The pre-roast considerations (ambient temperature, humidity, etc.)
Beginning of the roast to time and temperature of the beginning of chemical
reaction (i.e. color change and the beginning of the Maillard reaction)
The duration of the Maillard reaction until the beginning of first crack
The duration of the time between the beginning of first crack and the end of
the roast
The degree of sugar caramelization (represented as an end temperature off
the thermocouple reading bean mass, Agtron color, or other color
The role that thermodynamic pressure plays in the development of flavors
in coffee
There are other crucial points that I monitor, but they do not contribute
specifically to flavor development during roasting (though they contribute to my
ability to meet the profile). Although those points lay outside of the scope of this
publication, they are important to the actual act of roasting and could be covered
through independent consulting or by attending SCAA courses on roasting.
For much of the rest of this publication I will be breaking down and explaining
the significance of the deconstructed sections of the roast profile. Please note
that these sections are broken down based on their occurrence in the chronology
of the roast curve, and not based on level of flavor contribution in roasting.
2 Michael
Sivetz, Coffee Technology
(Westport, Connecticut: The AVI Publishing Company INC, 1979), 249
“The intrinsic potential flavors lie within the bean; the mechanisms of roasting
can only bring out what is there An oak log will still smell of oak volatiles; and
a hickory log will still smell of hickory volatiles.”3
I won’t go on much about green coffee because it isn’t the point of the
handbook, but sourcing great coffee is crucial. Or perhaps I should say, sourcing
coffee that meets your company’s goals and roasting program is of great
importance. If there is anything I have learned about roasting coffee, and
intentionally manipulating the flavor profile of the coffee through adjusting the
roast profile, I am left with the absolute impression that you cannot find
something that isn’t there. Though Sivetz says it perfectly in the above quote, let
me provide one more analogy. I like to think of a coffee like a color (let’s say
blue). You can only do so much to a coffee by manipulating a roast. You can turn
that blue into a teal, or a navy blue, or even a purple, but it will never be orange.
You will never make it better or substantially different than its potential, but you
can make it worse than its potential. If you wanted orange, you should have
sourced coffee that was red, yellow or orange. Source what you want, and
always make sure you are treating everyone in the supply chain (including the
Earth) with respect.
Michael Sivetz, Coffee Technology, 257
The first consideration roasters must make when I approaching the beginning of
the roast is considering the charge temperature and charge weight of the batch
they will be loading into the roaster. Charge temperature indicates the initial heat
value of the drum as read by the return air (exhaust air) probe on the roaster.
This is not a precise measurement of the total temperature, simply an
approximation of the temperature of the air after it has passed through the
roasting drum (ideally, indicating the heat of the air after either depositing heat
into or being heated by the metal in the roasting drum). One will need to modify
the charge temperature up or down for the following reasons: batch size, batch
number of the day, anticipated residual heat in the roasting system, and desired
heat application in the roast.
Typically, a smaller charge weight will call for a lower charge temperature, and
heavier weight will call for a higher temperature. Usually, the greater the batch
number for the day, the lower the required charge temperature (because of
thermal retention). Additionally, if you just roasted a dark roast coffee, you will
likely need a lower charge temperature for the following batch because of higher
heat retention in the system. Depending on the roast profile of the coffee you are
trying to roast (especially compared with the power output of your roaster), you
may need a higher / lower charge temperature in order to achieve the necessary
rate of rise (or modify your batch size slightly). The bottom line is, charge
temperature and charge weight will help the roaster establish the initial thermal
momentum of the roasting environment.
Another important indicator is your turn-around point. The turn-around point is a
piece of roast data that, while not a precise measurement, gives the roaster a
grasp of what is happening with the rate of heat transfer early in the roast. In a
roast profile, the turn-around point represents the bean probe’s rate of rise
hitting zero after sharply dropping for the first minute or so (results will vary
based on thermocouple type, thickness, and placement). At the beginning of the
roast, the bean probe is heated roughly to the environmental temperature of the
drum. When you add the room-temperature beans into the roaster (i.e. charge the
roaster), the bean probe readout begins to drop sharply. At the same time (though
we cannot see it in any readouts), the bean temperature is sharply rising from
room temperature to meet the thermocouple as it declines. The turn-around point
is the measurement of when and at what temperature the beans rise in
temperature equalizes with the thermocouple’s declining temperature, after
which the two rise together (called “turn- around,” “equilibrium,” or “delta
point”). The timing of the turn-around can help you understand the momentum
of the roast long before getting a true Rate of Rise (RoR) from the bean
temperature thermocouple. If the turn-around happens earlier than planned, you
are entering the roast with more thermal momentum than you may have expected
and should lower your heat application. This can also be true if the thermocouple
temperature reads abnormally high. If the turn-around happens significantly later
than it should, then you are probably lacking in thermal momentum and should
use slightly higher than normal heat application. Similarly, if the temperature for
turn-around is lower than normal, it may behoove you to use greater heat
application in order to meet the planned profile.
Though charge weight/ temperature and turn-around time/ temperature do not
directly cause flavor development in the roast specifically, they significantly
affect the rest of the roast. These factors do not have to be held in total constant
in order to match a roast profile or match flavor development; rather, the craft
and skill of the roaster manipulates them to maintain heat application in the early
stages of the roast.
After charging the roaster with beans, the thermocouple drops rapidly in
temperature until equalizing with the constant rise of the bean temp at a bean
temperature probe RoR of 0 degrees Fahrenheit. The readout then begins to rise
right along with the average surface temperature of the bean mass (and air), as
free moisture begins to be driven off the bean. For lack of better terminology, I
often refer to this as the drying phase. There are no real significant chemical
reactions happening; rather, water vapor is being driven off, pressure is
beginning to build and the thermal momentum of the batch is being established.
As enough moisture is driven off the bean, chemical reactions can begin and
color changes (specifically pale green/white to yellow) become visible on the
surface of the coffee bean. This color change is one of the first critical points of
measurement. Note the temperature at which the bean becomes yellow in your
roaster and try to use that thermocouple measurement to standardize your
notations. Noting the time and temperature of the beginning of chemical reaction
is absolutely critical to understanding development and helping to replicate that
roast at a later time.
Quick notes about this segment of the roast:
The “drying phase,” for lack of a better term, begins at the charge of the
roast and ends at the critical point noted as the beginning of chemical
reaction. This point is noted as the beginning of color change to yellow and
adoption of hay-like aroma. This signals the beginning of the Maillard
reaction and the measurement of our next critical segment.
Matching time from charge through drying to this point with other batches
of this coffee at this curve will help develop consistent thermal energy for
chemical reaction phases and make your job as the roaster operator much
If you know through experience that this coffee does not develop roast
defects if it is allowed to “dry” (i.e. drive off free moisture) until this point
(x amount of time allows for proper drying without causing roast defects),
then it will help to safeguard against negative flavor contributors like
scorching and tipping.
Tipping is caused by excessively rapid heat application; scorching is
caused by too high of a drum surface temperature during the charge of
the roast. It causes a toasty, grainy, burnt flavor.
Facing is another defect, in which coffee that has already gone through
color change is scorched. It may happen due to drum speed
(centrifugal force), drum overloading, or too high a rate of conductive
heat transfer. Facing causes burnt and char like characteristics in the
If the time from the charging of the roast to the beginning of chemical
reaction is too short, then the development of roasting defects like
scorching and tipping are more likely.
In addition, a shortened time frame will result in unevenly driven off
moisture, creating the potential for some inconsistencies in the
development of the flavors in the coffee.
If this time is too fast, then you may have too much energy within the
roasting system and will experience a “runaway” curve that does not
enable you to meet future goal times and temperatures for your roast
Consequently, if the time from the charging of the roast to the beginning of
chemical reaction is too long, it could result in a lack of pressure within the
bean during chemical reactions, which will result in deficient flavor
development in the coffee (i.e. a flat coffee).
An elongated drying time could result in a lack of thermal V momentum in
the roaster and make it impossible for you to achieve a solid match for the
rest of the roast curve you have planned.
Take care during the drying time, as you are not only trying to avoid certain
flavor defects stemming from roasting defects (tipping, scorching), you are
also trying to set yourself up for success later in the roast.
This first notation (beginning of chemical reaction) along the path of the roast
curve is not directly a control point to cause the development of positive flavors;
rather, it is a control point to help aid in the avoidance of negative flavor
contributions. Additionally, since this helps to further establish thermal
momentum in the roasting system, it indirectly causes the development of certain
other flavor contributors based on the fluctuations in the later roast curve caused
during this time. It is critical to understand your roasting system well through a
little trial and error (or expert advice) in order to determine optimum charge
temperatures, turn-around points and overall heat application to achieve ideal
results for the “drying phase” of roasting. The number of variables for each
unique situation are too great for me to cover; in this volume.
“A remarkable scheme of the Maillard reactions has been proposed by Hoge
(1953, 1967) who gives clear information on the mechanisms of this nonenzymatic browning reaction. Nursten (1981) proposed a classification system of
the Maillard reaction products: (i) ‘simple’ sugar dehydration/fragmentation
products (furans, pyrones, cyclopentenes, carbonyl compounds, acids); (ii)
‘simple’ amino-acid degradation products (aldehydes, sulfur compounds); (iii)
volatiles produced by further interactions (pyrroles, pyridines, imidazoles,
pyrazines, oxazoles, thiazoles, compounds from aldol condensations).”4
The Maillard reaction is one of the most chemically complex reactions that
occurs during coffee roasting. It more than doubles the number of volatile
aromatic compounds present in the coffee compared to the initial volatile
aromatic compounds in green coffee as well as produces a number of critical
intermediate and final products. This chemical reaction begins early in the roast
as amino acids act as catalysts with reducing sugars, resulting in a complex nonenzymatic sugar- browning process. As expressed by Andrea Illy and Rinantonio
Viani, “Water and carbon dioxide are generated by the very important Maillard
reaction, which leads to the coloured products, the melanoidins, and to the main
part of the organic volatiles.”5 These continue to change, react, change, and
react, creating a number of intermediate products as well as different chemical
compounds. For our purposes we will be considering the beginning of color
change to yellow to indicate the beginning of the Maillard reaction. This
chemical reaction will continue until it either runs out of compounds with which
to react, or is ended by the drop of the roast into the cooling tray (though it will
continue until the coffee is decently cooled; this is one of the reasons why it is
super important to have an effective cooling tray).
Though this reaction continues until the end of the roast, it is not productive for
us to measure it, since we are concerned about a number of different roast
phases. Thus, we will be measuring it from the beginning of color change to the
beginning of first crack. Taking into account the vast array of volatile aromatic
compounds created during this stage, in my mind some of the more important
compounds that are created are the melanoidins. There has been research into the
“...flavor binding, color, texture, and antioxidant properties of melanoidins and
investigation of the physiological effects and fate of melanoidins (COST,
2002).”6 In my opinion, the greatest contributions have to do with flavor, and
texture (think body). As the Maillard reaction continues, it generates more and
more melanoidins, which continue to modulate the complexity and perceived
body of the coffee (they have a high molecular weight, which correlates with
higher viscosity and thus thicker mouth-feel). By lengthening the roast during
this phase, you can increase the perception of complexity and body (and
modulate the way we perceive the flavors). By decreasing the time that the
Maillard reaction is permitted to occur, you can decrease the body and improve
the clarity of the coffee.
Quick notes about this segment (I call MAI) of the roast:
The measurement of this segment of the Maillard Reaction begins at the
initial color change point noted above.
This measurement ends when you can tell that the bulk of the coffee in the
roaster is beginning to enter first crack (the audible demonstration of sugar
The duration of the Maillard reaction is significant because this reaction
will continue to occur until either the roast is ended or it runs out of
The Maillard Reaction is caused by amino acids acting as catalysts with
reducing sugars, this chemical reaction continues to produce intermediate
products, which it then reacts with to produce other intermediate products.
This chemical reaction is likely responsible for well over 600 volatile
organic compounds within the finished product.
In addition, this reaction continuously produces melanoidins. These
high-molecular-weight browning products contribute flavor,
body/texture, color, bonding and complexity to the coffee. Specifically
to our experiments, they greatly modulate the experience of the body
of the coffee.
If you increase the amount of time that the Maillard reaction is allowed to
occur, you increase the complexity of the sugar browning tones you are
creating in addition to the weight/texture/mouth-feel.
Ex. Brown sugar turns to maple syrup turns to honey/ vanilla turns to
Though the specifics are different with every coffee (i.e. some just will
never have a honey-like tone or a vanilla bean in the finish), this
modulation of flavor holds true with all coffees.
When considering how to modulate this part of the roast curve, you should
consider what you taste in the cup, and then think about the human
experience of taste. Ask what a heavier mouth-feel would do to this coffee,
or what greater complexity could add or subtract from the experience you
are trying to craft. Also, consider how the heavier mouth- feel (viscosity)
and the increased complexity affect the clarity of the beverage.
In disclosing some detail about how I arrived at my conclusions, I would like to
share some of my cupping scores for a variety of experimental coffees in order
to help the reader understand the potential effects of altering the Maillard time.
In these experiments, I will talk about the differences made in the following
coffees: a Brazilian Micro-lot, a Mexican Organic, a SHG Guatemalan, and an
Ethiopian Kochere. All of these cuppings were done blind in our cupping lab at
Nossa Familia Coffee in Portland, Oregon. For these particular experiments, I
held the drying time, development time, and final temperature as constant as I
could (aiming for less than 10 second deviations) and manipulated only the time
spent ' in the Maillard-to-first-crack (MAI) phase. In the body score, I am listing
the qualitative (horizontal) score first (6-10) and following that with an intensity
score (1-5).
Body σ from
Score Baseline
Honeyed with clove, ginger, and cinnamon, cherry
Baseline 8 | 3 0:00
Cherry, with a seed-like savory spice, pie cherries and
7.5 |
graham cracker, floral, chocolate, slight merlot grape,
brown sugar, significantly less body.
Plum, seed like, sweet, herbaceous spices, drinking
8.5 |
chocolate, dark cherries, floral and fragrant, merlot
grape with heavy body.
Brazilian Micro-lot: In this experiment(my first), I tried to hold all things
constant with the exception of my time between color change and the beginning
of first crack. Though I was almost completely successful, I had one roast that
fell out of specification, yet helped to highlight the points I am making here.
Considering baseline time as 0:00 for Maillard reaction, the faster Maillard
reaction varied by -0:10, and the slower Maillard reaction by +0:39 (the out-ofspec-for-development- time experiment was +0:35). With the baseline roast, I
noticed the following: decent body (qualitatively an 8 on SCAA form) with a 3
for intensity of body. Descriptors I used for this coffee included chocolate,
honeyed, clove, tea-like, notes of cherry flesh and cinnamon spices, balanced.
The faster time for Maillard reaction was a 7.5 qualitatively and a 2 with regard
to intensity. Descriptors I used for this coffee were cherry, soft floral, seed-like,
graham cracker, very light-bodied. Meanwhile, my scores for the longer Maillard
reaction were an 8.5, and a 3 with regard to intensity. Descriptors I used were
plum, herby spices, drinking chocolate, dark cherry, heavy-bodied. Finally, since
it is relevant to this discussion, the accidental modulation of the “out of spec”
roast resulted in a 7.5 qualitative analysis, and a 4 with regard to the intensity of
the body. Descriptors used were chocolate, honeyed, and candied plum. There
was also a note about the heaviness of the body. There seems to be a clear trend
in this coffee to the modulation of a heavier body (and in this particular case, a
more pleasing qualitative analysis) with the increase in duration of the Maillard
reaction. Additionally, there is a change in the descriptors moving toward
“heavier” and more complex taste descriptors.
Fast MAI
7.5 |
7.5 |
Slow MAI 8 | 5
σ from
Sweet, caramel, rich red berries, floral, graham
cracker, red apple.
Sweet nut, perfumed floral, spice, molasses,
chocolate, green grape to apple.
Sweet, chocolate, brown sugar, fruit, warming
spice in aftertaste.
The Mexican Organic coffee displayed encouragingly similar results despite
differences in variety, altitude, processing method and microclimate. The
baseline once again is represented by 0:00. This time, the faster reaction is
represented by -0:08, and the longer reaction time by +0:26. The baseline roast
of this coffee scored as follows: 7.5 qualitative, and 3.5 with regard to intensity.
Descriptors used on this coffee include sweet caramel, rich red berries, floral,
graham cracker, and red apple. The faster of the reactions scored the following:
7.5 qualitative with a 4.5 intensity. Though this doesn’t match with the proposed
effects, the rest of the data would make this out to be an erroneous score (I am
only human). Also, the variance is under 0:10, which is part of the reason I
developed a 0:10 consistency standard. (I have trouble tasting variance if it is
within 10 seconds, so when production roasting I only consider variances of less
than 0:10 to be on target). The descriptors used for this one include sweet nut,
perfumed, floral, spice, green grape to apple. The longer Maillard reaction
yielded an 8 on the body with an intensity of 5. Cupping notes for this coffee
included sweet chocolate, brown sugar, fruit. Notice that once again we have not
only a shift in the intensity toward heavier body as we progress through a longer
Maillard reaction pre-first crack, but there is also a shift in the descriptors toward
weightier and more complex flavors.
Thirdly (and fourthly) is the experimentation with the SHG Guatemalan. Let’s
deal with the first round, and then we will move over to the second. During the
first round, baseline was 0:00, faster reaction was -0:29, and longer reaction was
+0:23. Please note I cupped this coffee 7 times, and this is a representation of the
average scores for these coffees. Baseline scored 7.75, with a 2.75 intensity.
Cupping notes for the coffee included sweet, citric, peach, floral, vanilla, white
tea, raw sugar, baking spice. The faster Maillard scored a 7 and an intensity of
2.5. Cupping notes for this coffee included dull, sweet, bland, floral, peach-like,
spices, seed-like, caramel. The longer Maillard reaction scored 7.625, and 3.5
with regards to intensity. Cupping notes used to describe this coffee included
floral, vanilla, peach, baking spices, baked peaches, cinnamon, honeyed,
chocolaty, tobacco, peach pie, mulled spices, coriander seed. In this example we
see again a trend toward increase in intensity of the body, alteration of
qualitative scores, and a modulation of descriptors from simple to complex, and
from light to heavy.
Body σ from
Score Baseline
7.75 |
Fast MAI
Slow MAI
| 3.5
Sweet, citric, peach flesh, vanilla, White tea,
floral, lime, molasses.
Sweet nut, perfumed floral, spice, molasses,
chocolate, green grape to apple.
Fruity, floral, vanilla, peach, baking spices,
vanilla, cinnamon, honeyed, chocolate, tobacco,
heavy, darker peach tones, mulled spices,
molasses, baked peaches.
Body σ from
Score Baseline
7.75 |
Peach pie, tea-like floral tones, pie spices,
molasses and honey (hints of caramel).
Peach preserves, cherry, hints of floral,
Fast MAI
cinnamon, clove, herbaceous spices, caramel
chocolate, syrupy.
Fruity peach (ripe), tea like, heavy floral tones,
Slow MAI
slight seed like and tea like characters, honey
| 3.5
like sweetness, very syrupy.
The second set of experiments with the SHG Guatemalan resulted as follows.
Baseline 0:00, faster reaction was -0:03, longer reaction was +0:41. Baseline
scored 8.5 with regard to quality and a 3.5 with regard to intensity. Descriptors
included peach pie, tea-like floral, molasses, honey and caramel, floral tones.
The faster Maillard reaction time scored an 8 for qualitative and a 4 for intensity.
Similar to the experiment with the Mexican, we have what appears to be an
outlier, but the differentiation is minimal and can be accounted for by the slightly
longer length in development time. The tasting notes for this roast were peach
preserves, hint of cherry, floral, cinnamon, clove, chocolate, molasses. The
scores for the longer Maillard reaction time were an 8 qualitative and a 2.5 for
intensity. This is an outlier in the true sense of the word. I can theorize as to its
presence, but I am better off just admitting the flaws in my cupping and indicate
to the reader that, despite this outlier, I still fully believe in the aforestated
trending and utilize it to this day. Tasting notes of this roast were fruited, ripe
peach, tea-like, heavy floral, honey and graham cracker, syrupy. There seems to
be a slightly similar trend to the descriptors despite the variation in the cupping
Kochere - Body σ from
Ethiopian Score Baseline
7.5 |
Fast MAI
Floral, white tea, honey, citrus, lemon, berry,
vanilla, butterscotch, bergamot.
Lemon, floral, vanilla, slight seed-like character,
cinnamon, orange, orange rind, floral, bergamot.
Slow MAI 8 | 3 +0:54
Chocolate, floral, nut, citrus blossom, malt, sweet
lemon meringue, berries, lemon bar, caramel,
Kochere Body σ from
Score Baseline
7.5 |
7.5 |
Fast MAI
Slow MAI
7.5 |
Floral, white tea, honey, citrus, lemon, berry,
vanilla, butterscotch, bergamot.
Lemon, floral, vanilla, slight seed-like character,
cinnamon, orange, orange rind, floral, bergamot.
Chocolate, floral, nut, citrus blossom, malt, sweet
lemon meringue, berries, lemon bar, caramel,
Finally, my experiments with the Ethiopian Kochere. This one provides us with a
particularly rich glance into the development occurring in the Maillard reaction
from beginning of color change to the beginning of first crack because in
addition to the dedicated experimental data, I have data from a number of
production runs with slight variations in Maillard reaction length. We’ll begin
with the experiment, and then I will branch out into discussing the other sets of
data. Baseline 0:00, faster development -0:11, and slower development +0z54.
Baseline scores a qualitative 7.5 (7.5 second cupping) with a quantitative 2 (4.5
second cupping).
The cupping notes for this roast are floral, white tea, honey, citrus, lemon,
vanilla, butterscotch, and bergamot. For the faster reaction time, the coffee
scored 8 (7.5) and a 3.5 (2) for intensity. Cupping notes for this coffee were
lemon, floral, vanilla, seed, baking spice, orange rind. Finally, the longer
Maillard reaction development scored an 8 (7.5) for quality and a 3 (3) for
intensity. The tasting notes for this expression of the coffee were chocolate,
floral, nut, citrus blossom, malt, sweet lemon, lemon meringue, caramel, and
vanilla. As with the other coffees, you can see a clear progression in terms of
complexity, and weight of flavors as well as a trend within the scoring.
With the Kochere specifically, I logged a number of intentional variances in our
production roasts. By pairing these with cupping notes reflecting not the SCAA
form interpretation but the flavor modulation, we can see a clear picture
beginning to develop. In this extensive listing of Maillard times with regard to
the baseline, a trend in flavor descriptors becomes apparent. Flavor moves from
less structured toward complex, and from lighter in weight/body to heavier.
Time Relative to Baseline
Flavor Profile
Cane sugar, honey, vanilla
Sweet honey, vanilla
Caramel, molasses, a lot of vanilla, buttery
Wild honey, vanilla, syrupy
Cane sugar, honey, vanilla
Cocoa nibs, honey, Wild honey
Cane sugar, agave nectar, buttery, vanilla bean
Caramel, vanilla bean
Cinnamon, butter, vanilla, baking spices
Honey-like, vanilla, butterscotch
Chocolate, malt, caramel, vanilla bean
At its core, this chart demonstrates the basis of my understanding of the role of
the Maillard reaction in the roasting of coffee. It increased the complexity of
chemical composition and the perception of body, resulting in the appropriate
modulation of the perceived flavor for the coffee drinker. In other words, you
could intentionally give a coffee a tea-like structure, or a caramel-like mouthfeel, or give it a heavy, buttery body all by modulating the length of time the
Maillard reaction is permitted to generate melanoidins.
Even so, there is no silver bullet here. Each coffee has within it a slightly
different chemical composition that will cause it to have different flavors and
potential for flavors. But in the end, they all will trend in the way I have
suggested. As a roaster, you have a great amount of control in how you will
present the coffees (what you are accentuating and what you are downplaying),
but you only have so much latitude. In order to land on certain flavor profiles,
you must be diligent and deliberate in your sourcing strategies and then use these
roasting strategies to draw out that potential.
Ivon Flament, Coffee Flavor Chemistry
(West Sussex, England: John Wiley & Sons, LTD, 2002), 39
Andrea Illy and Rinantonio Viani, Ed.,
Espresso Coffee: The Science of Quality Second Edition
(San Diego, California: Elsevier Academic Press, 2013), 192
Illy and Viani Espresso Coffee: The Science of Quality Second Edition, 204
Next we arrive at a point in the roast where the majority of coffee roasters will
feel a little more at home. Unlike other segments of the roasting curve I have
previously enumerated, this phase has a common name and designated start
point. Development time is set to begin at the beginning of first crack, and
measures the length of the roast to the drop (where coffee exits the roasting
chamber and enters the cooling tray). There are also a series of conventions
people hold about development time, but they are currently not universal within
the coffee industry.
To begin with, development time is actually very complex. It is not simply one
set of chemical reactions occurring; rather, it is a multi-dimensional interaction
between many separate chemical reactions that are not only happening on their
own, but also interplaying with one another. During this stretch of time, the
Maillard reaction is continuing and is now reacting somewhat differently, since it
is coming into contact with different new compounds that are being generated by
- other chemical reactions. Sugar caramelization, organic acid degradation,
Strecker degradation, and pyrolysis are all occurring simultaneously with the
ongoing Maillard reaction and causing a number of different changes in the
chemistry and flavor profile of the coffee. We will spend time in this section
focusing on the significant aspects of the roast that affect flavor development
during this stage.
Sucrose begins to undergo caramelization (at different temperatures depending
on the speed at which it is heated), forming water vapor and carbon dioxide
leading up to and continuing during first crack. Then, there is enough pressure in
the bean that we experience first mechanical crack. This is where the structure of
the bean fractures and begins to expand, leading to the rapid off-gassing of
reaction byproducts. Caramelization, which we will spend much more time
talking about in the next section, converts sucrose into caramel, and replaces the
sweetness of the sugar with a bitter and complex flavor. Sugar caramelization is
also important in that the degenerating sucrose forms acetic and formic acids,
among other byproducts. Joseph Rivera states: “Depending on actual roasting
conditions, acetic acid concentrations can increase up to 25 times its initial green
bean concentration. Overall acetic acid concentrations reach a maximum at light
to medium roasts, then quickly dissipate as roasting progresses due to its volatile
During this phase, we have the degradation of organic acids being quite
noticeable, specifically those in the chlorogenic acid group (CGAs) as well as
the loss of citric and malic acids. All of these are present in the green coffee and
begin to break down to form other organic acids as they decompose. Quinic and
caffeic acids would be great examples of acids generated due to CGA
breakdown. Likewise, the citric and malic acids present in the green coffee are
decomposed and partially form other organic acids like citraconic acid for citric,
and fumaric and maleic acids for malic. CGAs are responsible for a lot of the
bitterness in coffee stemming from the organic acid content. Citric and malic
acids tend to be more pleasant. Thus, the trick is to sufficiently decompose the
CGAs while retaining as much citric and malic acids as you prefer for your light,
acidic, enzymatic coffees. Phosphoric acid levels tend to stay about the same
during the roast (in other words, you have to use sourcing to control it). As noted
above, acetic acid is formed through sucrose caramelization, peaks, and then
begins to decline. The real trick to timing the length of development time for a
particular coffee is to understand the balance of organic acids you want to taste
in the cup, and modulate the length of development time to achieve that flavor.
Develop too rapidly and you will have excess CGAS remaining and experience
bitter and metallic acidic compounds; roast for too long, and the acidity will be
muted or less perceptible to your palate (or even become unpleasant).
Those more expert on organic chemistry than myself suggest the following:
“A great number of acids is generated by Maillard reaction or caramelization.
The most prominent are formic and acetic acids. ”8
“The predominant acids are chlorogenic, acetic, and citric.”9
“In brewed coffees, the acidity is largely due to homologous organic acids of
vinegar, namely acetic acid, propionic acid, butyric acid, valeric acid, etc, the
latter of which have strong and distinctive tastes."10
The final thing I’ll mention happening during this stage is pyrolysis, or the
thermal decomposition of compounds into their more basic compounds (and
eventually carbon) without the presence of oxygen. This reaction begins shortly
after first crack and continues until the end of the roast. Pyrolysis could be a
contributor to what some consider to be a “roast” flavor if it becomes too far out
of balance with other compounds in the final product.
As we can see, there is a lot going on during this phase of the roast. This is
perhaps Why the development phase has been, to this point, one of the areas of
greatest focus and scrutiny by most people in the roasting community. When this
segment of the roast has been modified, the reactions I feel make the greatest
impact on my tasting coffees have been the organic acids and the volatile
compounds formed by the Maillard reaction. Though sugar caramelization and
pyrolysis are also occurring during this segment of the roast, I will specifically
focus on them in the next chapter of this handbook.
In order to demonstrate my findings, I will amalgamate information from my
cupping trials of the same coffees listed in the Maillard reaction section. Once
again, the acidity scores represent SCAA cupping form scores (6-10) and the
second number represents the experience of intensity of the acidity (1-5).
Acidity σ from
Score Baseline
Honeyed with clove, ginger, and
8.5 | 3 0:00
cinnamon, cherry flesh.
Chocolate, Concord grape, floral, sweet,
tangy, strong acidity (citric?) honey,
Fast Development 7.5 | 5 -0:57
musk melon, grape to candied plum
Honey, plum, seed-like, molasses, melon
6.5 |
Slow Development
to grape, slightly tart, lighter in body
with heavy chocolate tones. Low acid.
Brazil Micro-lot
With my initial experiments in the exploration of the different segments of the
roast curve, I was encouraged by the trends I was seeing and their logical nature.
I was able to significantly vary the development time of the coffee and taste that
variation in the cup. With the fast development, I was able to increase the speed
of the time in “development” and reach the terminal temperature 57 seconds
sooner than I did with the baseline roast. The result was a more intense
experience of acidity with a lower qualitative score. With this particular roast, I
did accidentally vary the length of MAI time +0z35. This contributes to the
chocolate notes and candied plum (increased complexity and experience of body
over the baseline significantly). With the slow development time, I was able to
match roasts and vary only the length of time in “development” phase. This
resulted in a significantly lower experience of the acidic intensity of the coffee,
and a much lower qualitative score. Here we see the overall flavor profile of the
coffee moving from a lighter, more tannic and bitter acidity to a sweeter and
more rounded experience, and finally to an almost nonexistent experience of
Acidity σ from
Score Baseline
Sweet, caramel, rich red berries, floral,
graham cracker, red apple.
Ginger, cinnamon, apple-white pear, soft,
Fast Development 7 | 4
nutty, slightly vegetal.
Sweet, spicy, berry-like fruit to red apple,
Slow Development 6.75 | 3 +0:19
mulled cider, slightly heavier body.
Organic Mexican
We see similar results with the second experiment. I was exceptionally fortunate
to keep the roasts for these experiments almost completely on track. The other
segments of the roast (outside of development time, which I was intentionally
modifying) were within 0:10 of baseline, and the amount I was able to cause the
development time to deviate Was significant. We see (with regard to actual
score) a similar intensity score between the baseline and the fast development
time; however, we also see a significant variation in the qualitative score of the
one with faster development.
Accompanying this lower score, we also see the presence of vegetal tones. I
would conjecture that these vegetative tones could be linked to excess
chlorogenic acids (CGAs) remaining in the coffee. When comparing the baseline
to the slower development time, we see a significant decrease in the intensity of
the acidic composition, as well as a lower qualitative score. The liveliness of the
acidity is diminished as well. In this experiment, we see the manipulation of
development time causing a modulation in the experience of the acidity from
intense to less intense, from lower in quality to higher in quality, and then
sinking off once again, and a modulation of the composition of the organic acids
from vegetal and bitter to balanced, to diminished.
Acidity σ from
Guatemalan Score Baseline Notes
Sweet, citric, peach flesh, vanilla, white tea,
8.5 | 4 0:00
floral, lime, molasses.
Cocoa nibs, floral, sweet, candied peaches,
8.25 |
lime, citrus, seed like, lemon-lime, brown
Development 3.75
Sweet, tobacco floral, raisin, baked peaches,
6.25 | 3 +0:23
maple, vanilla, butter, canned peaches.
With the first experiment with the SHG Guatemalan coffee, I was able to keep
the development time experiments within 0:10 for all other segments of the
roast, and varied it by more than 0:10 (though only slightly with one of the
coffees) with the development time. With the faster development time, I was
barely faster than the development time for baseline. The baseline’s peach and
citric tones take on a slightly more bittering characteristic and change to lime, or
lemon-lime-like acidity with candied peach. In extending the development time,
the citrus tones fade into the background and more complexity and tones
associated with body come out. The citric tones fade, and peach flesh becomes
baked peaches, the tea floral becomes more tobacco-like, etc. This is a great
example of how a roaster can shift the development time to modulate the flavor
of the coffee in small and nuanced ways.
Acidity σ from
Score Baseline
Peach pie, tea-like floral tones, pie spices,
8.5 | 4 0:00
molasses and honey (hints of caramel).
Bright citrus, lime-peach, dried peach to
mango like acidity, tea-like, seed-like, honey,
graham cracker, sweet, floral, peach.
Cooked peaches, chocolate and brown sugar,
sweet syrup, sweet, slightly flat.
Between the baseline and the faster development time, the difference is quite
significant, but the experience of intensity and quality is not that different.
However, it continues to illustrate a similar point when you begin to look at the
flavor descriptors. The faster development time has a greater experience of citric
acid (and even a slightly bitter citric acid with the lime), the stone fruit or peach
even shifts to allow the cupper to experience mango. With the longer
development time, we notice a more expected outcome with regard to the
qualitative and intensity score. They are both lower in score than the baseline.
Once again we see a shift from bitter to sweet citric, to more balanced and sweet
acidic compounds, and eventually to their decline. There is a shift in the
experience of depth and complexity of tones as the development time lengthens
and the Maillard reaction continues to do its thing.
Kochere Ethiopian
Acidity Score
8.5 | 4
Fast Development 7 | 3.5
Slow Development 6.5 | 4
Kochere Ethiopian (2)
Acidity Score
7.5 | 3.5
Fast Development 7.5 | 4.5
Slow Development 7 | 3
σ from
Floral, white tea, honey, citrus,
lemon, berry, vanilla, butterscotch,
Sweet, citrus, slight sweet corn,
cocoa nibs, lemon cake, lemon
blossom, wild honey, orange.
Lemon, chocolate, earthen,
coriander seeds, flat, dull, slight
σ from
Floral, white tea, honey, citrus,
lemon, berry, vanilla, butterscotch,
Sweet, citrus, slight sweet corn,
cocoa nibs, lemon cake, lemon
blossom, wild honey, orange.
Lemon, chocolate, earthen,
coriander seeds, flat, dull, slight
The final dedicated experiment was with the Ethiopian Kochere. Represented
above are two different cupping scores on the coffee. In the first cupping, we see
another round of successful roasts for the experiment (matching other times
within 0:10, and varying development time by at least 0:10). The baseline
compared with the faster development time shows either a decline or a similarity
with regard to qualitative evaluation, and (at least in the second cupping) a
significant increase in the intensity of the experience of the acidity. There is also
a shift from the more straight-forward lemon and berry in the baseline to a
heavier citrus (and potentially a more bitter citrus experience) with the shift
toward orange. The floral tea- like and bergamot characteristic devolve into a
more simplistic blossom. When comparing the baseline with the slower
development, we see coriander seeds take over for the floral tones as “fragrant”
tones dominate, and many of the interesting notes from the coffee begin to soften
and dull. This, once again, confirms the suspected trend we are noticing with
flavor development during the modulation of “development” time.
Finally, as with the segment on Maillard reaction, I want to compare roast data
on the Ethiopian Kochere that I conducted by slightly varying our production
Time Relative to
Flavor Profile
Seed-like, corn, orange, lemon, honey, citrus, musty.
Orange, tangerine, bitterness, hibiscus floral.
Orange, floral, tea-like.
Bergamot, seed-like, lavender, floral, lemon, orange,
seed, orange rind.
Lime, lemon, bergamot, tea-like.
Citrus, lemon, blossom, tea-like.
Lemon, Meyer lemon, honeysuckle, Earl Grey tea,
bergamot, floral.
Lemon, hibiscus, bergamot, tea-like.
Sweet lemon, bergamot, lavender, floral.
Seed-like, lemon, slight lemon, soft, earthiness.
Basically speaking, we can see that there is a correlative effect between the
length of the development time and the perception of the organic acids present in
the coffee. CGAs tend to cause bitterness and, in my opinion, the
slightly underdeveloped coffees tend to have more bittering present. Ivon
Flament says, "In summary, the conclusions were that chlorogenic acid
contributed to body and astringency ...”11 (This note about body could be linked
to the idea that some of the CGAs end up entangled in melanoidins.12). The
experience of bitterness due to low development time can go from metallic
bitter/vegetal bitter, to a pleasing bitterness (like from an orange or grapefruit
rind think tannins) with more development, then a better balance of acids such as
citric, malic, acetic, etc. - thus giving some sweet tones to the acidity in the
coffee, which go from sour to sweeter before eventually beginning to dull as you
approach a deeper development. The longer you go with development time, the
lower the concentrations of organic acids and the more soft and round the
experience of acidity and fruit. An overly fast development time will tend to
yield bitterness from the organic acid balance (whether metallic or vegetal) and
the overdeveloped will soften or neutralize the experience of organic acids
present in the cup, dulling the “liveliness of the coffee.” In my opinion, the
interplay of degrading CGAs, citric and malic acids with the developing acetic
represent the greatest bulk of organic acid contribution to flavor.
With regard to Maillard reaction byproducts during this phase, we can see the
transition from lack of floral tones (or more aggressive, less-structured floral
tones) to more structured and softened tones. As a general rule of thumb, the
longer the Maillard reaction is allowed to continue, the more complexity and
texture (with regard to mouth-feel) one could expect from a coffee. This tends to
be true whether it is reacting within the MAI Time (Color Change to First Crack)
or the development times.
Quick notes about the time from the beginning of first crack and
the end of the roast:
This is a really complex matter for the following reasons:
The Maillard reaction is continuing and is now reacting differently as
it comes in contact with new reactants being produced by sucrose
caramelization, organic acid degradation and pyrolysis. For our
purposes, this is why we break the Maillard reaction into pre-first
crack and post-first crack. Additionally, in my experiment / observe /
record / repeat approach, I am unable to independently modulate the
Maillard reaction’s activities post-first without altering the other
chemical reactions mentioned.
As noted, sucrose (the primary sugar in coffee) is undergoing
caramelization. As caramelization occurs, the sugar breakdown creates
complexity and bitter/ complex caramel compounds as well as volatile
organic compounds.
Organic acid degradation is occurring as well, with chlorogenic acid
groups breaking down and forming other organic acids (acetic, quinic,
etc.), citric and malic acid degrading, etc. The length of time from the
beginning of first crack to the end of the roast will have a lot to do
with the final organic acid composition of the coffee’s flavor profile.
Pyrolysis is also occurring during this stage of the roast. This is the
thermal breakdown of chemical compounds into their simplest forms
due to heating. Eventually what pyrolysis means is the breakdown of
all compounds into carbon and volatile residues. As heat continues to
decompose everything, the coffee continues to evolve.
It is really difficult to wrap all of that information up into a nice, neat little
ball to tell someone what the adjusting of the development time of a coffee
will do to overall flavor. In my experience, the two most significant
adjustments to the flavor profile of a coffee come from the organic acid
composition, and the complexity caused by the Maillard reaction interacting
with these new reactants and intermediate products.
In general, the way organic acids tend to shift is as follows (with
relation to “development time”):
Bitter and vegetal
Bitter and citric/malic/other more pleasant acids
Bitter and citric/malic/other more pleasant acids and sour
Citric/malic/other more pleasant acids, and sweet and sour
Citric/malic/other more pleasant acids and sweet
An example of this shift is as follows:
Bitter, unpleasant copper coin taste, strongly acidic but
Bitter, unpleasant, slight hint of something vegetal (hops)
Citrus rind (like grapefruit rind)
Grapefruit or lime-like
Meyer lemon with a hint of rind
Meyer lemon
Lemon shake-up (if you’ve never had one, you should try it)
Sweet, more toward melon
Low to no acidity
The way that the Maillard reaction influences this is by modulating the
complexity of the beverage:
Introduction of more floral or fragrant tones to the coffee. The
suggestion would be that a longer development time should
accentuate these nuanced floral/fragrant/seed-like tones.
Conversely, a faster development time should hinder the ability of
the Maillard reaction to create complexity within this flavor range
and provide ' an even greater accentuation to the acidity/ fruit
tones. However, at a certain point, the acidity will be
disconnected from our experience with flavor because of the onedimensional nature of an overly fast development time. This
could result in bitter, vegetal tones or the experience of metallic
tones associated with the acidity.
Rivera, Joseph. “Acetic Acid.”
Accessed December 22, 2014.
Illy and Viani, Espresso Coffee: The Science of Quality Second Edition, 197
Sivetz, Coffee Technology, 252
Michael Sivetz, A Critique on the Causes and Decline of: Coffee Quality
(Sivetz, 1996), 68
Flament, Coffee Flavor Chemistry, 37
Illy and Viani, Espresso Coffee: The Science of Quality Second Edition, 195
Part of the development time of the roast (the ending, to be precise, but meriting
its own section here) includes the choice of degree of caramelization to which
one would choose to roast. Essentially we are asking the question, “How much
of the sucrose should we take to the point of caramelization as the heat travels
inward in the seed?” The degree of caramelization in the coffee seed seems to be
connected heavily to the final temperature to which you are roasting. I say this
because, through much tasting, sweetness seems preserved with some long and
drawn-out development times, but seems easy to cover up or degrade with
higher-end temperatures and at different rates of development times. In other
words, the sweetness, level of caramelization/pyrolysis is disconnected to a great
degree from the length of “development time.” Therefore, we will be treating
terminal temperature as its own particular beast.
Coffee contains primarily sucrose with regard to the makeup of its sugar content.
How much of that sucrose do you intend to caramelize, and how much of it do
you plan to retain as residual sugars, which help give coffee natural sweetness?
If the bean temperature does not reach high enough, there remains the chance for
vegetal flavor contributors to remain in the coffee. This could be due to a lack of
pyrolysis of certain compounds that can lend vegetal tones to coffees. It could
also be because the strength of the caramel tone in the coffee is not enough to
obscure the compounds causing us to taste vegetation in our coffee.
Conversely, too much caramelization and, eventually, too much pyrolysis leads
to an excessive amount of bitterness and flattens the complexity of the coffee.
You are left playing a delicate game.
Here are notes from one experiment with a SHB Guatemalan I did specifically to
test this theory.
Deviation of Roast:
Roast Phase
Baseline Low Drop High Drop
Drying Phase
σ End Temperature
-6 F
+6 F
Please notice above that all of the deviations from the baseline roast are quite
acceptable, and to my ability to taste should have little to no effect on the flavor
of the roasted coffee. The only significant contributor should be the final
temperature (simultaneously representing the degree of caramelization and
SCAA Cupping Form:
Sweetness Overall
10 10
10 10
10 10
Fragrance Flavor After Acid Body Balance Uni
Baseline 8.25
Within the qualitative score numbers on the SCAA cupping form, there
definitely seem to be slight qualitative differences that end up resulting in a
significant difference in overall score. With the roast profile that I was using,
What these numbers seem to indicate is that there is a range of pyrolysis and
caramelization that is more desirable, and ranges on either side of that “sweet
spot” that are less desirable.
Intensity Scores:
Low Drop
High Drop
It is worth noting here that the intensity scores are not modified or changed
greatly. This would also suggest that the intensity of these elements are not
connected with the final degree of roast, but rather with the actual curve
representing the path the coffee follows through roasting.
Flavor Descriptors:
Herbaceaous Sweetness Body
pie spices
and honey, tea-like
garden pea / sweetlight, very
vegetal toward
cucumber and honey or
raw sugar honeyed
sweet, rich chocolate,
sesame seed-like
chocolate jagged
molasses seeds
green tea,
pie spices,
Finally, when looking at how the flavor profile of the coffee changes, we see
significant differences forming between the coffees. The lower drop temperature
results in vegetal tones because of lack of caramelization and pyrolysis
(specifically, pyrolysis reducing or eliminating contributors to a vegetal taste
profile). The coffee roasted to a lower terminal temperature did tend to remain
sweeter, but lacked some of the complexity and balance brought about by the
greater caramelization/pyrolysis. The deeper levels of sugar caramelization and
pyrolysis gave the darker of the two roasts a more savory characteristic with
more bitterness from the caramels. The path that flavor development seems to
follow is from vegetal and sweet, to sweet and not vegetal, toward mild, toward
slightly bitter, then toward bitter.
Bottom line is, whatever you are going for in a roast, approach it with caution
and consideration when choosing your final end temperature. Also keep in mind
that darker flavors, greater complexity and heavier body can be made without
burning coffee!
Additionally, remember that the SCAA Coffee Taster’s Flavor Wheel can
provide a helpful guide to understanding the progression of coffee flavor through
the caramelization process. Early on (with relation to end temperature / degree of
caramelization), you start with more “enzymatic flavor tones” residual from the
terroir of the coffee and the balance of chemical compounds in the plant. (Bear
in mind that enzymatic flavor tones are not created during roast, but may be
covered up do to caramelization, pyrolysis, etc.) As you continue to caramelize,
you will shift into the sugar browning section of the taster’s wheel and these
flavors will become more dominant. Finally, if you continue
caramelization/pyrolysis you will arrive in the section marked “dry distillation”
which is due to the pyrolysis and carbonization of volatile aromatic compounds
among others in the seed.
The degree of sugar caramelization is the final point of consideration within
my paradigm for controlling the flavor development during coffee roasting.
By controlling your final roast degree, you are essentially controlling
how much or how little sugar you are allowing to be turned into
Unlike organic acids, which seem to be more greatly
affected by time (with regard to their development or decomposition),
sugars seem to need the addition of heat to the environment in order to
caramelize to a greater extent.
Essentially, the lower the end temperature, the more residual sugar is
left in the coffee, contributing to a sweeter cup.
Conversely, the higher the end temperature, the more caramels you
have developed — reducing sugar, adding complexity, and balancing
the sugar content with bitter compounds.
On the low end of proper caramelization lie vegetal tones. These can
be connected with development time as well; if a coffee is
underdeveloped, the sweetness takes on a more vegetal characteristic.
This could be tomato, cucumber, garden pea, etc.
On the high end of proper caramelization, pyrolysis flavors begin to
dominate, and chocolate and deep caramel tones become ashen and
The SCAA Flavor Wheel tends to work decently well in understanding
what flavor range you will be experiencing at certain levels of
With lower levels of sugar caramelization, you will have a
heavily sweet coffee with notes in the floral and fruity range
(unless you mess it up; then vegetal).
Medium-range sugar caramelization will accentuate caramel,
chocolate, vanilla, nut, and the like.
Higher levels of caramelization lead to pyrolysis and the
destruction of volatile aromatics, resulting in super dark
chocolate, woody, carbon, and ashen.
Finally we come to a more abstract, but very important facet of coffee roasting
(one which is somewhat new to me and I think many in the industry). This is the
concept of being intentional as to how we build up pressure in the coffee seed
while roasting. An offhand comment by Illy and Viani in Espresso Coffee: the
Science of Quality got me thinking about the importance of building up pressure
in coffee: a build-up of pressure within the bean is important for the generation
of sufficient aroma.”13 I also saw a note in Coffee Flavor Chemistry saying;
“Kaufman (1951) observed that pressure formed in the beans during roasting is
necessary to the proper development of coffee flavor.”14 I had previously been
considering it because of my understanding of the tipping defect. When we are
roasting coffee, the heat is not instantaneously being applied evenly to the
surface of the coffee seed; rather, it is being applied in a gradient (starting from
the outside and working into the middle of the coffee seed).
When we are roasting and heating the coffee, we are also attempting to drive off
free moisture by turning it into steam and forcing it out of the seed. This is due
to the fact that drying the coffee is necessary for desirable chemical reactions
(such as the Maillard reaction) to occur. As we drive off that moisture, and as the
heat infiltrates the bean, it forms a wall of pressure forced from the outside
moving in. If the seed isn’t dense enough the handle the pressure being placed
upon it, the steam begins to vent out of the softest part of the bean, the tip where
the embryo would have germinated had the coffee seed been planted. As the
steam exits rapidly, it causes charring around that soft spot--the defect we know
as tipping (avoid it).
Illy and Viani describe this process as follows: “The temperature of the bean
surface increases — with heat conduction into the porous material — due to the
temperature gradient. When the local temperature reaches the evaporation
temperature of the bean moisture, a front of evaporation starts moving toward
the center of the bean. During the first part of the roasting process the walls of
the whole bean are still relatively firm. Thus the vapor that has been generated
cannot permeate and the pressure buildup makes the bean volume expand.
Mechanical and thermal stresses moving toward the K center of the bean are
created, which makes the beans crack [not necessarily referring to first crack] or
even burst if the superposed stresses overcome the tensile strength of the
bean.”15 In addition to causing a potential defect or problem, this buildup of
pressure completely changes how a coffee roasts.
But how can something like pressure change how coffee roasts and tastes? The
answer is fairly simple but difficult to fully grasp. Pressure changes the rate of
chemical reaction, and the effectiveness of certain chemical reactions that occur
during coffee roasting. The interesting thing about this is that you begin to create
this pressure wall at the moment you begin to drive off steam, the moment when
no chemical reactions are taking place: namely, the moment you charge the
drum. Even though the “drying” time doesn’t matter directly for the flavor
development in coffee (as there are no real chemical reactions during that time
other than the potential for defect), you are not only establishing your
momentum for the rest of the roast, but also for the potential reaction rate and
potential byproducts of the roast itself.
Essentially, increasing the pressure on a chemical reaction involving gasses will
increase the rate of reaction. This is because you are forcing the compounds into
closer proximity and will cause the chemical reactions to occur much more
rapidly. In addition, an increase in pressure will help bring the coffee to higher
overall temperatures internally, as pressure tends to increase temperature. This
will also cause an increase in the rate of many chemical reactions. For our
purposes, we are especially concerned with the reactions (and reaction rate) of
the volatile aromatic compounds being modulated, specifically increasing
reaction rate through shorter overall roast times, producing desirable results by
compressing the aforementioned roast segments. Though it may seem odd, the
amount of pressure built up can be significant! “The high temperature (usually
170-230 C for 10-15 min) and the elevated pressure inside the bean (up to 25
atm [ 25 bar for former baristas or 367 psi]) trigger a vast number of chemical
reactions...”16 One notable exception is the Maillard reaction, specifically with
regard to the formation of melanoidins, whose importance we covered earlier.
Research independent of coffee has demonstrated that an increase of pressure
will actually hinder the chemical reactions involved in the Maillard reaction,
stating, “In conclusion it appears that the volatile products of the Maillard
reaction are generally suppressed by the application of high pressure...”17 and
specifically will hinder the development of melanoidins. “Retardation of the rate
of decomposition of the ARP (Amadori rearrangement products) in forming
melanoidins was further confirmed in the present work...”18 which increase the
perception of complexity and body. Thus, you will tend to have lower
complexity and lower experience of body in fast roasts, which have increased
internal bean pressure. This is in contrast to medium or slower batches (that are
still within a reasonable time frame) which will have a heavier body and a
greater amount of complexity.
The dichotomy of how chemical reactions function under pressure could mean
that there is an acceptable way to scale the time we permit certain chemical
reactions to occur to arrive at a similar sort of flavor in the coffee. That being
said, the scaling will never be perfect, as parts of the Maillard reaction will
actually occur more slowly during faster roasts.
It is essentially a tradeoff. The faster you roast, the less body and complexity you
will have; but you can still roast quite rapidly and not have vegetal and
“underdeveloped” (i.e. grassy, vegetal, super bitter) coffee. This lends credence
to certain perspectives that roasts can be broken down into percentages or ratios
in order to achieve similar qualitative results. While this theory may function to
a degree, it would be better to maintain the same buildup of pressure by
maintaining a similar overall roast time in order to preserve consistency from
roast to roast.
Notes on pressure buildup in the coffee seed during roasting:
The buildup of pressure is essential for the proper formation of volatile
aromatic compounds, and the function of many chemical reactions during
coffee roasting.
Coffee beans have been shown to reach up to 25 atm (25 bar) pressure,
according to Illy.
The pressure buildup comes from the speed at which the coffee is being
roasted within the system. As heat is being applied to the coffee, water
begins to come off the coffee in the form of steam. This buildup of steam,
along with the traveling wall of heat, create a pressure wall within the
roasting bean.
The amount of pressure changes the rate of chemical reaction (specifically
for the Maillard reaction). This results in some of the same reactions
occurring at a much more rapid rate. It also inhibits certain reactions from
occurring (specifically mentioned are generation of melanoidins).
This means that the amount of time needed for certain chemical reactions
during coffee roasting could be shortened relative to the speed at which the
coffee was roasted(lending some credence to the idea of applying
overarching percentage breakdowns of the coffee roast).
Reactions reducing vegetal aspects of coffee or negative organic acids could
be accelerated (allowing for “well developed” coffee), while others
resulting in body and complexity could be hindered.
Therefore, if done knowingly, it is possible to achieve well developed
coffee at a much faster roast, though you will necessarily be sacrificing
certain aspects of coffee flavor development.
In a number of respected sources, such as Illy, I have seen the idea
presented that the pressure wall building up in the bean causes the chemical
reactions to operate differently, and higher pressure is preferred for flavor
development (obviously without creating defect).
Illy and Viani Espresso Coffee: The Science of Quality Second Edition, 184
Flament, Coffee Flavor Chemistry, 37
Illy and Viani Espresso Coffee: The Science of Quality Second Edition, 180
Illy and Viani Espresso Coffee: The Science of Quality Second Edition, 198
Mark Bristo and Neil S. Isaacs, “The Effect of High Pressure on the
Formation of Volatile Products in a Model Maillard Reaction,” Journal of the
Chemical Society, Perkin Transactions 2, (1999): 2218, accessed November 6,
2014, doi : 10.1039/A901186B
Bristo and Isaacs, “The Effect of High Pressure on the Formation of Volatile
Products in a Model Maillard Reaction,” 2217 doi: 10.1039/A901186B
In summary, I want to leave you with a list covering specifics important to this
approach to controlling flavor development during roasting, so you can make
adequate efforts to shift your roast profile in a direction to your liking.
“Drying Phase”
After the charge of beans into the pre-heated drum until the beginning
of color change to yellow
Responsible for causing some roast defects (scorching, tipping, etc.)
Sets up the roast’s momentum for the remainder of the time
Contains no true chemical reactions
Begins to establish pressure wall as it heats the bean and boils off
“MAI” Phase
Short for Maillard reaction phase (though it is not an accurate
measurement of the entire length of the Maillard reaction)
Begins at the beginning of color change to yellow and the adoption of
a hay-like aroma
Ends at the beginning of the notation of development time (at the
beginning of first crack)
Incredibly chemically complex series of chemical reactions
Responsible for development of melanoidins, among other aromatic
and volatile aromatic compounds Strecker degradation of amino acids
Less time in this phase results in lower body and reduced complexity
(less complex and lighter flavors)
More time in this phase results in heavier body and increased
complexity (more complex and heavier flavor)
“Development” Time
Begins at the beginning of the batch going into first crack (the batch,
not outlier beans)
Ends at the end of the roast
Very complex series of events
Maillard reaction is continuing and now has new reactants, thanks
to other reactions
Organic acid degradation: CGAs, citric and malic acid Organic
acid formation: Acetic (from sucrose), quinic (from CGAs),
formic, and others.
Caramelization of sucrose
Focus was primarily on organic acids and Maillard-reaction products
Organic Acids
Try to strike a balance between the loss of chlorogenic Acids to
the point of losing bitterness and vegetal acidic flavors, and
losing the beneficial citric and malic acids.
Tends to move from metallic and vegetal bitter acidic compounds
to sour and more pleasing compounds, to sweet and more
pleasing, to sweet and more dull, to dull, to low acid.
Maillard reaction
Specifically focus on development of floral and fragrant tones
during this phase, along with some browning tones caused by the
Maillard reaction
Complexity of floral tones increase with lengthened development
Presence of browning tones not formed through caramelization
increases with a longer development time
Sugar Caramelization and Pyrolysis
Focusing primarily on sucrose caramelization and thermal
Related primarily to the terminal temperature of the batch of
coffee (not specifically the time).
As more sucrose caramelizes (higher end temperature), the lower
the sweetness and the more bitterness and complexity.
The less sugar caramelizes, the more sweetness and less bitterness
is revealed, but the coffee will have less complexity as well.
If you roast with too low of a temperature, you run the risk of not
sending unwanted compounds through pyrolysis and could end up
with vegetal attributes and some bitterness in your coffee.
If you reach too high of an end temperature, you may have more
pyrolytic tones in the coffee than intended, and you run the risk of
tasting carbon or ash.
By establishing pressure in the bean through controlling the
overall speed of the roast and thus the overall roast time, you are
able to scale the length of the reactions you will need in order to
achieve certain flavors.
Faster roast = higher pressure, more compressed times needed for
“MAI” and “development,” However, the Maillard reaction will
not be as effective, so you will miss out on some compounds
contributing to body and overall complexity. You run the risk of a
one-dimensional coffee.
Slower roast = lower pressure, so you will need longer times for
some chemical reactions to take place and potentially should
scale the MAI time and the development time accordingly. The
Maillard reaction will function well and melanoidins will be
present to contribute to complexity and body.
At the end of the day, you pay your money and you make your choice. I don’t
want to tell you the “best way to roast coffee” because there is no such thing.
These are meant to be guidelines to help you get your coffee how you want it to
taste. I hope it was a helpful journey for you, and I hope my experiences and
words can help lead you to a better cup of coffee in your future.
Through the intentional use of these guideposts and general trends, roasters can
make rather informed decisions as to where to start roasting a coffee based on
cupping the pre-shipment and arrival samples, and then make small, educated
tweaks to different parts of the roast curve as discussed above to land where they
are hoping to land with their coffee’s flavor profile. As a friend of mine has
always said, “there are no silver bullets,” but at least we are able to develop
vague guidelines.
I have been using this approach for over three years for all my product
development, sample roasting and production roasting. I have yet to run into a
circumstance where it has not been true. There have been small shifts I have had
to make along the way when confronted with more detailed evidence, or
interesting sides to coffee roasting I hadn’t initially experimented with. But we
are always learning and always in process.
Although I am continuing to monitor a number of different aspects of roasting in
addition to the process described above, this handbook details what I have found
to be pertinent to help an experienced roaster understand flavor development in
When it comes to understanding flavor, and how I perceive and describe flavors,
I think it is worth detailing my paradigm here as well. I do not think in terms of
raw chemical compounds causing me to taste certain things; rather each taste
reveals a complex mess of experiences that remind me of things that I have
tasted before. In the handbook, you may read that the taste/flavor shifted from
lemon to lime to me. What this means is that I had a greater bittering experience
than I did when I experienced lemon, because I find limes to be slightly more
bittering. Similarly, I would say citrus rind is more bittering than the flesh, so I
could describe the difference as lemon to lemon rind. Another example: If I taste
peaches, and then something with greater complexity and a syrupy body, I would
likely call it peach pie or cobbler. This is because these flavors have a syrupy
mouth-feel, often have molasses (more complex and slightly more bitter than
sugar), etc.
What I am getting at is, when you find yourself applying the style of roasting I
discuss in this handbook, it is more beneficial to think about how you experience
taste and how these guidelines will modulate that experience, than to look at
only the specific chemical reactions being discussed. Once you come to grips
with how you experience taste, you can willfully change the details surrounding
the coffee’s flavor profile into what you want or need.
Professional editing: Kelly Stewart
Book layout and design: Mark Carter
Some interior photos by:
Lucas Chemotti
Connie Blumhardt