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This paper is a concise review of the research on coffee flavour to serve as a rapid reference on the subject. It covers the process of roasting coffee beans, the volatile and non-volatile components generated by the process and the chemical reactions responsible for their formation. Volatile compounds significant on the determin-ation of coffee aroma are given according to the most recent research. Finally, the paper discusses the chemical indexes used over the years to characterize coffee flavour deterioration and estimation of shelf-life.
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COFFEE FLAVOUR: AN OVERVIEW 99
Copyright © 2004 John Wiley & Sons, Ltd. Flavour Fragr. J. 2004; 19: 99–104
FLAVOUR AND FRAGRANCE JOURNAL
Flavour Fragr. J. 2004; 19: 99–104
Published online 4 February 2004 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/ffj.1325
* Correspondence to: R. A. Buffo, Department of Food Science, Faculty of
Agricultural and Food Sciences, University of Manitoba, 250 Ellis Building,
Winnipeg, MB, Canada R3T 2N2.
E-mail: rabuffo@hotmail.com
Coffee flavour: an overview
Roberto A. Buffo1,* and Claudio Cardelli-Freire2
1Department of Food Science and Nutrition, University of Minnesota, St. Paul, MN, USA
2Meals and Sides Division, ConAgra, Los Angeles, CA, USA
Received 21 June 2001
Accepted 28 October 2003
ABSTRACT: This paper is a concise review of the research on coffee flavour to serve as a rapid reference on the
subject. It covers the process of roasting coffee beans, the volatile and non-volatile components generated by the
process and the chemical reactions responsible for their formation. Volatile compounds significant on the determin-
ation of coffee aroma are given according to the most recent research. Finally, the paper discusses the chemical
indexes used over the years to characterize coffee flavour deterioration and estimation of shelf-life. Copyright © 2004
John Wiley & Sons, Ltd.
KEY WORDS: coffee flavour; volatiles; non-volatiles; chemical indexes
Introduction
Coffee is a tropical plant that grows at 600–1800 m
above sea level.1 It is native of Ethiopia, from where
it spread first to India and then to Indonesia, Brazil,
Colombia and Central America.2 What we commonly
know as ‘coffee’ is a beverage prepared by brewing
roasted, ground beans. The plant produces red cherry-like
fruits containing two seeds, which, after being separated
from the fruit pulp, are known as ‘green coffee’. They
are packed in sacks and transported to consuming
countries. When received, they are blended with green
beans from other origins and roasted to produce the
characteristic flavour and colour associated with coffee
beverage.3
Roasting
Green coffee beans lack the colour and characteristic
aroma of roasted coffee; both are formed during the
roasting process. Coffee oil, which comprises about 10%
of the roasted beans, carries most of the coffee aroma.
The aroma is made up of a complex mixture of volatile
compounds, whereas non-volatiles determine sourness,
bitterness and astringency.4
The roasting process can be roughly divided into three
phases:2
1. An initial drying phase, evidently endothermic, during
which moisture is eliminated. The smell of the beans
changes from green to peasy to bread-like, and the
colour turns yellowish.
2. The actual roasting phase, during which a number of
complex pyrolytic reactions take place. The chemical
composition of the beans is drastically modified, with
release of large amounts of carbon dioxide and the
formation of the many hundreds of substances asso-
ciated with coffee aroma and taste. The beans change
colour to a dark brown. Initially the process is
exothermic. Pyrolytic reactions reach a maximum
of 190–210 °C, when the process becomes endo-
thermic with the release of volatile compounds. The
overall reaction becomes exothermic again at about
210 °C.
3. A final rapid cooling phase to stop the final exother-
mic part of the roasting operation, using air or water
as the cooling agent.
The quantity of heat transferred to the beans is a very
influential parameter of the roasting process. This can
be controlled by the roasting temperature and time. The
colour of the beans is directly correlated to the final
roasting temperature: the higher the temperature, the
darker the coffee, so that colour can be used to define the
end of the operation. The degree of roasting is usually
described as being ‘light’, ‘medium’ or ‘dark’. Roasting
time may be as long as 40 min, as is often the case in
Brazil, or as short as 90 s in fast roasting to produce
high-yield coffees. Roasting time influences the reactions
within the bean: longer roasting periods produce a bitter
coffee lacking a satisfactory aroma, whereas very short
roasting periods may be insufficient for the completion of
100 R. A. BUFFO ET AL.
Copyright © 2004 John Wiley & Sons, Ltd. Flavour Fragr. J. 2004; 19: 99–104
all pyrolytic reactions, resulting in coffee with under-
developed organoleptic characteristics.2
Chemical Composition of Roasted Coffee
The chemical reactions that take place during roasting
have not been completely elucidated. This results from
the extreme difficulty of reproducing or simulating in the
laboratory all the reactions that take place inside a bean,
since:
1. Not all the active precursors of aroma, colour and
taste present in green coffee have been identified.
2. The very large number of precursors give rise to com-
plex reactions, difficult to isolate, since intermediate
products react further.
3. Most reactions take place within intact bean cells,
which have very thick walls. These walls are com-
parable to autoclaves, where the pressure can only be
guessed.2
Roasting produces a net loss of dry matter, primarily
as gaseous carbon dioxide, water and volatiles products
of pyrolysis. There is a considerable degradation of poly-
saccharides, sugars, amino acids and chlorogenic acids,
and a moderate relative increase in organic acids and
lipid content. Roasting also produces high levels of
caramelization and condensation products. Caffeine and
trigonelline (N-methyl nicotinic acid) concentrations
remain almost unchanged.5
Non-volatile Components
As aforementioned, chemical components of roasted
coffee can be grouped into volatile and non-volatile sub-
stances, some of the former being responsible for the
aroma and the latter for the basic taste sensations of sour-
ness, bitterness and astringency. The non-volatile com-
pounds in roasted coffee are:2,5,11
1. Caffeine, which contributes to the strength, body and
bitterness of brewed coffee.
2. Trigonelline and its two non-volatile derivatives:
nicotinic acid (of nutritional value) and N-
methylnicotinamide.
3. Proteins and peptides that did not undergo Maillard
reaction.
4. Polysaccharides, namely cellulose, hemicellulose,
arabinogalactan and pectins, that play an import-
ant role in the retention of volatiles and contribute to
coffee brew viscosity.
5. Humic acids or melanoidins, as final products of the
Maillard reaction between amino acids and mono-
saccharides; they are the brown-coloured substances
that impart to roasted coffee its characteristic colour.
6. Carboxylic acids, mainly citric, malic and acetic, re-
sponsible for sourness.
7. Chlorogenic acids, mainly cinnamic, caffeic, ferulic,
isoferulic and sinapic, and their main degradation
product, quinic acid, all responsible for astringency.
8. Lipids, including triglycerides, terpenes, tocopherols
and sterols, that contribute to brew viscosity.
9. Minerals, with potassium being the most abundant
(around 40% w/w). Metals such as manganese (10
50 ppm), iron (15 40 ppm) and copper (2–5 ppm)
may catalyse reactions occurring during roasting and
storage.
Carbon Dioxide
Carbon dioxide is quantitatively the most important non-
aroma-contributing volatile compound in roasted coffee.
It is generated by pyrolysis and the Strecker degradation
reaction.6 The amount is dependent on the degree of roast
and can be up to 10 ml/g coffee.7 This gas is released
slowly in whole beans but rapidly after grinding. Because
it has a zero dielectric constant, carbon dioxide is very
soluble in the coffee matrix. Its loss from the bean is
most likely due to relationships between temperature and
the glass transition state in the system, although this later
physical effect has not been explored.
After coffee grinding, much of the carbon dioxide pro-
duced during roasting is released. A suitable degassing
time (2–8 h) must be applied before packaging using her-
metic containers. Efficient degassing of roasted ground
coffee is critical when it is packaged in flexible bags
without vacuum. If the time for degassing is too short,
the package can swell, losing appearance and even burst-
ing. To solve this, gas valves can be placed in the wall
of plastic bags to allow the release of carbon dioxide.8
It has been reported that 45% of the carbon dioxide is
released during the first 5 min after grinding.9 One work
in the literature states that 1.21 ml/g carbon dioxide and
0.002 ml oxygen/g roasted ground coffee (Arabica) were
released during the first hour after grinding.10 As particle
size decreases, the release of carbon dioxide is facilitated
because of greater surface-to-volume ratios. A decrease
of particle size from 1000 to 500 µm has been reported
to double the release of the gas.7 Pressurization with
nitrogen and carbon dioxide itself helps to prolong the
shelf-life of espresso coffee, because it maintains carbon
dioxide inside the coffee cells, avoiding cell wall damage
and further flavour release.11
Volatiles
The mechanisms of formation of coffee aroma are
extremely complex and there is clearly a wide range of
COFFEE FLAVOUR: AN OVERVIEW 101
Copyright © 2004 John Wiley & Sons, Ltd. Flavour Fragr. J. 2004; 19: 99–104
interactions between all the routes involved. The major
mechanisms include:2,12,13
1. Maillard reaction (non-enzymatic browning): a reac-
tion between nitrogen-containing substances on the
one hand (proteins, peptides, amino acids, seroto-
nine and trigonelline) and reducing carbohydrates,
hydroxy-acids and phenols on the other, to form
aminoaldoses and aminoketones by condensation.
2. Strecker degradation: a reaction between an amino
acid and an
α
-dicarbonyl with the formation of an
aminoketone that condenses to form nitrogen hetero-
cyclic compounds or reacts with formaldehyde to
form oxazoles.
3. Breakdown of sulphur amino acids, viz. cystine,
cysteine and methionine, that are transformed into
mercaptans, as well as thiophenes and thiazoles,
after reacting with reducing sugars or intermediate
products of the Maillard reaction.
4. Breakdown of hydroxy-amino acids, viz. serine and
threonine, able to react with sucrose to form mostly
alkylpyrazines.
5. Breakdown of proline and hydroxyproline, that react
with intermediate Maillard products; the former gives
pyridines, pyrroles and pyrrolyzines, whereas the
latter forms alkyl-, acyl- and furfurylpyrroles.
6. Degradation of trigonelline, forming alkyl-pyridines
and pyrroles.
7. Degradation of the quinic acid moiety, forming
phenols.
8. Degradation of pigments, mostly carotenoids.
9. Minor lipid degradation, primarily diterpenes.
10. Interaction between intermediate decomposition pro-
ducts (mostly unknown).
Aroma Volatiles in Roasted Ground Coffee
Active research on the volatile composition of coffee has
taken place in the last 25 years with the advent of gas
chromatography–mass spectrometry. The principal classes
of aroma compounds in roasted ground coffee are listed
in Table 1.
Significant Contributors to Aroma
The identification of new volatiles in roasted coffee may
well become an exercise in futility because the central
issue is to determine the chemicals effectively respons-
ible for coffee aroma.12 Gas chromatography–olfactometry
(GCO) techniques, such as AEDA (aroma dilution extrac-
tion analysis) and CharmAnalysis™ have allowed the
individualization of those key odorants by directly sniff-
ing the chromatographic eluent. From the list of around
80 compounds proposed by Holscher and Steinhart,26
Table 1. Classes of volatile compounds identified in
roasted coffee
Sulphur compounds
Thiols14
Hydrogen sulphide15
Thiophenes (esters, aldehydes, ketones)16
Thiazoles (alkyl, alcoxy and acetal derivatives)17
Pyrazines
Pyrazine itself18
Thiol and furfuryl derivatives19
Alkyl derivatives (primarily methyl and dimethyl)20
Pyridines
Methyl, ethyl, acetyl and vinyl derivatives14
Pyrroles
Alkyl, acyl and furfuryl derivatives14,21,22
Oxazoles23
Furans
Aldehydes, ketones, esters, alcohols, acids, thiols, sulfides and in
combination with pyrazines and pyrroles24
Aldehydes and ketones
Aliphatic and aromatic species25
Phenols26
Semmelroch et al.,13 using AEDA, selected only 14
compounds to reproduce coffee aroma based on odour
activity values (OAV), i.e. the ratio of concentration to
odour threshold (Table 2). Deibler, Acree and Lavin27
used CharmAnalysis™ to signal 30 potent odorants in
brewed coffee, of which 18 compounds were identified
by comparing their mass spectra, odour activity and
Kovát’s retention indices with those of authentic stand-
ards (Table 3).
Semmelroch and Grosch28 quantified these potent
odorants in ground roasted Arabica and Robusta coffee
and in the corresponding brews, finding that a change in
aroma takes place from roasted to brewed coffee due to
a shift in the concentration of the odorants. The polar
odorants, e.g. 4-hydroxy-2,5-dimethyl-3(2H)-furanone,
were preferentially extracted, whereas the yield of the
unpolar ones, e.g. 3-isobutyl-2-methoxy pyrazine, (E)-
β
-
damascenone and 2-furfurylthiol, was low. On the basis
of the quantitative data obtained, these authors formulated
synthetic mixtures (aroma models) for the Arabica and
Robusta brews. The models smelled clearly coffee-like
and reproduced the differences in the odour profile of the
original brews.
For roasted Arabica coffee, Czerny, Mayer and
Grosch29 carried out sensory assessments of model
systems of 27 odorants in an oil/water mixture. An
expert sensory panel evaluated the changes in the
overall odour after omission of one or more odorants.
These omission experiments indicated that 2-furfurylthiol,
4-vinylguaiacol, several alkylpyrazines, furanones,
acetaldehyde, propanal, methyl propanal and 2- and 3-
menthylbutanal had the greatest impact on the flavour
of ground coffee. In contrast, the absence of 2,3-
butanedione, 2,3-pentanedione,
β
-damascenone and vanil-
lin in the aroma model according to the corresponding
102 R. A. BUFFO ET AL.
Copyright © 2004 John Wiley & Sons, Ltd. Flavour Fragr. J. 2004; 19: 99–104
Table 2. Odour activity values (by AEDA) and formation mechanisms of volatiles in
the aroma of roasted ground Arabica coffee13
Compound Odour activity value Formation mechanism
(E)-
β
-Damascenone 2.7 × 105Carotene degradation
2-Furfurylthiol 1.7 × 105Maillard reaction
3-Mercapto-3-methylbutylformate 3.7 × 104Maillard reaction
5-Ethyl-4-hydroxy-2-methyl-3(2H)-furanone 1.5 × 104Maillard reaction
4-Hydroxy-2,5-dimethyl-3(2H)-furanone 1.1 × 104Maillard reaction
Guaiacol 1.7 × 103Phenol degradation
4-Vinylguaiacol 1.1 × 103Phenol degradation
Methional 1.2 × 103Maillard reaction
2-Ethyl-3-dimethylpyrazine 1.6 × 102Maillard reaction
2,3-Diethyl-5-methylpyrazine 95 Maillard reaction
3-Hydroxy-4,5-dimethyl-2(5H)-furanone 74 Maillard reaction
Vanillin 48 Phenol degradation
4-Ethylguaiacol 32 Phenol degradation
5-Ethyl-3-hydroxy-4-methyl-2(5H)-furanone 21 Maillard reaction
omissions was not noticed by the assessors. This study
confirmed for the most part the compounds previously
identified by Semmelroch et al.13 with the exception of
(E)-
β
-damascenone, the compound with the highest odour
activity value. Although the degradation of carotenoids
that generates
β
-damascenone has been regarded as
having a major importance on tea flavour and is even
suggested to play an important role in coffee aroma as
well,30 sensory studies did not validate this possibility.
In a follow-up study, Mayer, Czerny and Grosch31
quantified the most potent odorants in brewed medium-
roasted Arabica coffee. In accordance with previous re-
sults,28 the more polar compounds yielded much larger
amounts than the unpolar ones (>75% vs. <25%, respect-
ively). An aroma model was prepared based on these
results for the brew. In triangle tests, the model contain-
ing all 24 odorants was compared with a set of models
missing one or more compounds using the afore-
mentioned omission tests. These experiments indicated
that the aroma of the brew was mainly caused by
some alkylpyrazines, furanones and phenols, and by
2-furfurylthiol, methional, and 3-mercapto-3-methylbutyl
formate. The higher impact of methional and formate and
the lower aroma activity of 4-vinylguaiacol were in con-
trast to the results previously obtained for ground coffee
of the same provenance and roast degree.
Finally, Mayer and Grosch32 quantified 22 potent
odorants in the headspace of roasted Arabica coffee pow-
der, and a model mixture was prepared accordingly.
When evaporated, the similarity of the aroma of the
model to that of the roasted coffee headspace was scored
2.6 on a scale of 0 (no similarity) to 3.0 (identical). The
model included odorants such as acetadehyde, methyl-
propanal, 2- and 3-methylbutanal, 2,3-butadione, 2,3-
pentadione, 2-furfurylthiol, 2-ethyl-3,5-dimethylpyrazine
and 2,3-diethyl-5-methylpyrazine.
Chemical Indicators of Sensory
Deterioration
The onset of sensory staleness is used to determine the
end of shelf-life of roasted ground coffee.9 Staleness
in coffee is defined as ‘a sweet but unpleasant flavour
Table 3. Aroma occurrences resulting from CharmAnalysis27
Compound OAV (standardized) Sensorial description
Sotolon 81 Toast
β
-Damascenone 98 Fruit
2-Furfurylthiol 100 Toast
4-Vinylguaiacol 62 Cloves
2-Methyl-3-furanthiol 89 Nuts
Vanillin 71 Vanilla
Guaiacol 77 Plastic
Furaneol 58 Caramel
Methional 43 Potato
3-Methoxy-2 isobutyl pyrazine 38 Plants
2,4,5-Trimethylthiazole 38 Plastic
Abhexon 44 Honey
4-Ethyl guaiacol 31 Spice
5-Methyl-6,7-dihydrocyclopentapirazine 22 Cotton candy
2-Ethyl-3,5,-dimethylpyrazine 25 Burnt
cis-2-Nonenal 27 Toast
2-Isopropyl-3-methoxypyrazine 14 Green
2,3,5-Trimethylpyrazine 15 Toast
COFFEE FLAVOUR: AN OVERVIEW 103
Copyright © 2004 John Wiley & Sons, Ltd. Flavour Fragr. J. 2004; 19: 99–104
and aroma of roasted coffee which reflects the oxidiza-
tion of many of the pleasant volatiles and the loss of
others; a change in the flavour and the acid constituents
causing a partial bland tone’.33 Since the late 1950s
when the gas chromatographic work on coffee aroma was
initiated, a great evolution in analytic and data pro-
cessing techniques has occurred, and different staling
indexes have been developed and correlated to sensory
deterioration.
‘M/B’ Aroma Index
Raymond et al.34 defined the M/B aroma index as the
quotient of the concentrations of methylfuran and 2-
butanone. This ratio decreased from 2.6 to 0.1 within 4
days in roasted ground coffee dissolved in water at 23 °C
and 30 °C, which led to the suggestion that the M/B
index could be used as an indicator of staling. However,
no sensory results were presented and, in fact, this was a
storage study of a ‘coffee solution’ and not the roasted
ground coffee itself. Later Vitzthum and Werkhoff35
found a linear correlation (r2 = 0.96) between M / B
and a sensory index reported on a 1–5 scale (5 = best,
1 = worst) for the aroma of roasted ground coffee stored
at 20 °C in air (unstated moisture).
Further studies focused on the influence of the degree
of roasting and origin of coffee on the M/B index.
Kwasny and Werkhoff36 observed that the M/B index
determined in one kind of coffee might not be directly
applied to others. An empirical exponential function was
used to correlate the M/B index with degree of roasting:
M/B = a (degree of roasting)b
Robusta a = 31.3 b = 0.59 (r = 0.9999)
Salvador a = 20.5 b = 0.49 (r = 0.9898)
Kenya a = 21.9 b = 0.52 (r = 0.9900)
Colombia a = 28.4 b = 0.60 (r = 0.9951)
Furthermore, Spadone and Liardon37 reported that the
M/B index decreases continuously irrespective of storage
temperature or oxygen partial pressure in the package
(metal cans at 5% moisture, unstated basis). However,
correlations between M/B index and sensory evaluation
of brewed coffee prepared from the stored samples did
not show a linear trend, thus undermining the validity of
the parameter.
Flavour Quality Index (FQI)
Looking for a better index, Spadone and Liardon37
applied multiple linear regression to results of volatile
composition of roasted ground coffee vs. time of storage,
and defined a flavour quality index (FQI) based on five
key volatiles, viz. hexanal, vinylpyrazine, pyrrol, furfuryl-
methylketone and pyridine, with a good fit of their sen-
sory data (r2 = 0.87).
FQI = 6.53 + 0.027 [hexanal] 0.08 [vinylpyrazine]
0.04 [pyrrol] 0.022 [furfurylmethylketone]
0.001 [pyridine]
Nevertheless, the equation was only an experimental fit
and did not have a theoretical basis.
‘M/M’ Aroma Index
Vitzthum and Werkhoff35 defined the M/M aroma index
as being the ratio of the concentrations of methanol to 2-
methylfuran. This index showed an inverse linear relation
with the M/ B index and has been used to follow coffee
staling in industrial settings.
‘S’ Aroma Index
Radtke and Piringer38 defined the ‘S’ aroma index as the
sum of the concentrations of 2-methylpropanal, 3-
methylbutanal, diacetyl and 2-methylfuran, determined by
gas chromatographic analysis of the static headspace of
10 g coffee dissolved in 40 ml water at room temperature.
They also found a linear correlation between the index
and sensory evaluation by a panel of experts.
Sulphur Compounds as Aroma Index
Steinhart and Holscher39 applied headspace profile ana-
lysis in combination with a computer-aided discrimin-
ant analysis to evaluate aroma freshness of roasted
whole coffee beans in non-air-tight packs at 20 °C. Their
results indicated that aroma freshness of whole roasted
coffee is mainly determined by certain low-boiling com-
ponents, namely low-molecular Seight sulphur com-
pounds, Strecker aldehydes and
α
-dicarbonyls. The loss
of aroma freshness was due to the loss of certain aroma
impact volatiles, mainly methanethiol, which then could
be used as an indicator of freshness. The heavier com-
ponents, such as furfurylmercaptan, will remain in the
coffee and will cause an ‘ageing’ note. In addition, an
increase of dimethylsulphide, the oxidation product of
methanethiol, was observed, although no ‘true’ staling
compound was found.
Summary
Past research on coffee flavour has built a significant
knowledge base. About 900 volatile compounds have
104 R. A. BUFFO ET AL.
Copyright © 2004 John Wiley & Sons, Ltd. Flavour Fragr. J. 2004; 19: 99–104
been identified, although less than 20 of them have been
found to be relevant to coffee aroma. In addition, chem-
ical indicators of sensory deterioration have been pro-
posed and validated. Future research efforts will probably
focus on the elucidation of mechanistic and kinetic para-
meters for the formation and deterioration of key aroma
compounds. This would translate into practical guidelines
for producing and maintaining a good coffee aroma.
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... However, the coffee's intrinsic quality is predetermined in the green bean by its precursor composition, and the roaster only can unlock the full potential by applying the appropriate and optimised roasting conditions. Optimising the appropriate roasting conditions is undoubtedly the most critical ways for achieving the desirable coffee aroma [60]. Fobe and his co-workers [61] reported that as the roasting time is extended, the following changes occurred: the sugar content is reduced and then raised; caffeine contents showed insignificant changes; protein continuously decreased; free fatty acid improved; and unsaponifiable compounds declined. ...
... Fobe and his co-workers [61] reported that as the roasting time is extended, the following changes occurred: the sugar content is reduced and then raised; caffeine contents showed insignificant changes; protein continuously decreased; free fatty acid improved; and unsaponifiable compounds declined. Another report mentioned that the lipid and organic acid increased, while the trigonelline and caffeine content showed almost unchanged [60]. During roasting net losses of matters in the form of water vapour, CO 2, and volatile compounds are exhibited. ...
Chapter
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Coffee is one of the most important agricultural commodities in the world. The coffee quality is associated with pre-harvest and post-harvest management activities. Each step starting from selecting the best coffee variety for plantation until the final coffee drink preparation determines the cupping quality. The overall coffee quality influenced by the factors which involve in changes the physicochemical properties and sensorial attributes, including the post-harvest operations. The post-harvest processing activities contribute about 60% of the quality of green coffee beans. The post-harvest operations include pulping, processing, drying, hulling, cleaning, sorting, grading, storage, roasting, grinding, and cupping. This chapter comprises the harvest and post-harvest operations of coffee and their impacts on coffee quality.
... On the other hand, espresso coffee drinks demonstrate higher scores in the mouthfeel (astringency) (score from 3.1 to 4.7) than arabian coffee drinks (score from 2 to 3.2). The non-volatile components (such as caffeine, polysaccharides and chlorogenic acids) are the ones that contribute to the taste of coffee and, particularly, are responsible for the appearance and the sense of astringency [35]. ...
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Coffee is one of the mostly consumed beverages worldwide. Roasting of coffee is an important process causing many changes in the quality and sensory characteristics of coffee beans. The objective of this study was the determination of the effect of roasting on the physicochemical and sensory properties and comparison of six coffee varieties, namely Brazil Santos, Brazil Rio Minas, Mexico Finca Muxbal, Guatemala Shb Ep, Ethiopia Djimmah, and India Robusta. Coffee beans were subjected to heat treatment at air temperatures up to 270 °C for up to 20–27 min, depending on the coffee variety and the desirable roasting degree. During the whole process, various physicochemical properties (mass, volume, density, color) and sorption isotherms of coffee beans were measured. For sensory evaluation, arabian and espresso beverages were prepared. Color of coffee beans darkened with increasing time and temperature during roasting, while volume increased. Total mass loss was also observed. Sorption isotherms followed type III, except for the variety India Robusta and the raw samples that followed type II. Sensory characteristics were distinctly different for each of the studied varieties. In arabian coffee drinks the color of cream was darker compared to espresso drinks and presented less acid and sour taste. Concerning texture, the body was positively evaluated both in arabian and espresso drinks. Graphical abstract
... Roasting is considered as the most important step in determining the characteristic aroma, flavor and color of the coffee bean (Buffo and Cardelli-Freire, 2004). However, because a large number of complex interactive chemical reactions occur, it is still difficult to completely elucidate which and how the chemical precursors contribute to the final sensory qualities of the beverage. ...
Article
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The coffee beverage is the second most consumed drink worldwide after water. In coffee beans, cell wall storage polysaccharides (CWSPs) represent around 50 per cent of the seed dry mass, mainly consisting of galactomannans and arabinogalactans. These highly abundant structural components largely influence the organoleptic properties of the coffee beverage, mainly due to the complex changes they undergo during the roasting process. From a nutritional point of view, coffee CWSPs are soluble dietary fibers shown to provide numerous health benefits in reducing the risk of human diseases. Due to their influence on coffee quality and their health-promoting benefits, CWSPs have been attracting significant research attention. The importance of cell walls to the coffee industry is not restricted to beans used for beverage production, as several coffee by-products also present high concentrations of cell wall components. These by-products include cherry husks, cherry pulps, parchment skin, silver skin, and spent coffee grounds, which are currently used or have the potential to be utilized either as food ingredients or additives, or for the generation of downstream products such as enzymes, pharmaceuticals, and bioethanol. In addition to their functions during plant development, cell walls also play a role in the plant's resistance to stresses. Here, we review several aspects of coffee cell walls, including chemical composition, biosynthesis, their function in coffee's responses to stresses, and their influence on coffee quality. We also propose some potential cell wall-related biotechnological strategies envisaged for coffee improvements.
... Roasting is considered as the most important step in determining the characteristic aroma, flavor and color of the coffee bean (Buffo and Cardelli-Freire, 2004). However, because a large number of complex interactive chemical reactions occur, it is still difficult to completely elucidate which and how the chemical precursors contribute to the final sensory qualities of the beverage. ...
Article
Full-text available
The coffee beverage is the second most consumed drink worldwide after water. In coffee beans, cell wall storage polysaccharides (CWSPs) represent around 50 per cent of the seed dry mass, mainly consisting of galactomannans and arabinogalactans. These highly abundant structural components largely influence the organoleptic properties of the coffee beverage, mainly due to the complex changes they undergo during the roasting process. From a nutritional point of view, coffee CWSPs are soluble dietary fibers shown to provide numerous health benefits in reducing the risk of human diseases. Due to their influence on coffee quality and their health-promoting benefits, CWSPs have been attracting significant research attention. The importance of cell walls to the coffee industry is not restricted to beans used for beverage production, as several coffee by-products also present high concentrations of cell wall components. These by-products include cherry husks, cherry pulps, parchment skin, silver skin, and spent coffee grounds, which are currently used or have the potential to be utilized either as food ingredients or additives, or for the generation of downstream products such as enzymes, pharmaceuticals, and bioethanol. In addition to their functions during plant development, cell walls also play a role in the plant’s resistance to stresses. Here, we review several aspects of coffee cell walls, including chemical composition, biosynthesis, their function in coffee’s responses to stresses, and their influence on coffee quality. We also propose some potential cell wall–related biotechnological strategies envisaged for coffee improvements.
... Sample t40, t60 and t80 were significantly and positively correlated with bitterness. One of the components that contributes to the bitter taste in coffee is caffeine (Buffo and Cardelli-Freire, 2004). The steaming process carried out in this study resulted in reduced caffeine content. ...
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In addition to being a source of freshener, coffee has an enormous possibility to be developed as a source of antioxidants for functional beverages. However, efforts to increase the value added of coffee as a health functional drink are still hindered by the presence of high level of caffeine, which is thought to have adverse effects on health, especially for coffee lovers who are vulnerable to caffeine. This study aims to optimise the steaming duration to produce low caffeine coffee while maintaining the sensory attributes and antioxidant compounds contained in it. Indonesian Arabica (Leksana variety) green coffee beans were steamed with multi-level steaming durations (0, 20, 40, 60 and 80 min) followed by roasting (medium-dark roast degree), grinding, and brewing (espresso method). The results indicate that caffeine content in the coffee was inversely proportional to the steaming duration. The lowest caffeine content was obtained from the treatment of 80 min steaming with a decrease of caffeine level up to 28.73%. However, the longer process of steaming caused a significant decrease in polyphenol content and antioxidant activity. The hedonic test shows that the steaming treatment of coffee can increase preferences of panellists. There were two driving attributes that influence the overall liking of coffee, namely: bitterness and aftertaste. Coffee obtained from the treatment of 60 min steaming was most preferred by panellists. The results of APLSR biplot mapping show that there was a big change in almost all attributes in the coffee samples after 40 min steaming.
... It is possible that there is some degree of masking of attributes from the sour-and bitter-tasting compounds that overpower some of the other more delicate flavors, which then appear to increase once those masking compounds are flushed out of the grounds. Caffeine 26 and bitter, astringent chlorogenic acids 27 are highly soluble and would be in high concentrations in early fractions. Organic acids contributing to sour taste would be soluble early extractors as well. ...
Article
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Background: The composition of drip brew coffee versus brewing time has been chemically characterized in previous studies, and it is known that the total dissolved solids (TDS) systematically decreases with each fraction during the brew. Little information exists regarding the corresponding sensory attributes versus time, however, and it is unclear how TDS correlates with flavor profile. Results: Standard drip brews were fractionated into distinct samples by switching in an empty carafe every 30 seconds during the brew. Using a trained sensory descriptive panel, we found that most taste and flavor attributes decreased with brew time, e.g., the earlier fractions were systematically more bitter and more sour than later fractions. Surprisingly, however, several flavor and taste attributes increased in time, e.g., later fractions were systematically sweeter and more floral than earlier fractions. Since later fractions had lower total dissolved solids (TDS), these results indicate that perceived sweetness in drip brew coffee is negatively correlated with TDS. Mass spectrometry measurements of the monosaccharide content in the brews showed that none of the fractions had perceptible concentrations of any monosaccharide. Conclusion: The results of the sensory analysis and the monosaccharide analysis suggest that perceptible sweetness in coffee is a consequence of masking effects and/or the presence of sweet-associated aromas and flavors. The results further suggest that unique flavor profiles could be obtained from the same coffee grounds by judicious combinations of specific fractions. This article is protected by copyright. All rights reserved.
... For example, carbohydrates and free sugars suffer pyrolysis, thermal and Maillard (with proteins and amino acids) reactions generate aroma precursors such as furanes, carboxylic acids, pyridines, pyrroles, pyrazines, thiazoles and ketones. Ferulic, caffeic and quinic acids from chlorogenic acids were degraded to produce phenols, and lipids through oxidation were transformed to alcohols, ketones and aldehydes [2,[43][44][45][46]. Interestingly, we detected a high number of lipids influencing the sensory attributes of coffee beverage. ...
Article
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Genetic improvement of coffee plants represents a great challenge for breeders. Conventional breeding takes a too long time for responding timely to market demands, climatic variations and new biological threads. The correlation of genetic markers with the plant phenotype and final product quality is usually poor. Additionally, the creation and use of genetically modified organisms (GMOs) are often legally restricted and rejected by customers that demand natural products. Therefore, we developed a non-targeted metabolomics approach to accelerate conventional breeding. Our main idea was to identify highly heritable metabolites in Coffea canephora seedlings, which are linked to coffee cup quality. We employed a maternal half-sibs approach to estimate the metabolites heritability in open-pollinated plants in both leaves and fruits at an early plant development stage. We evaluated the cup quality of roasted beans and correlated highly heritable metabolites with sensory quality traits of the coffee beverage. Our results provide new insights about the heritability of metabolites of C. canephora plants. Furthermore, we found strong correlations between highly heritable metabolites and sensory traits of coffee beverage. We revealed metabolites that serve as predictive metabolite markers at an early development stage of coffee plants. Informed decisions can be made on plants of six months old, compared to 3.5 to 5 years using conventional selection methods. The metabolome-wide association study (MWAS) drastically accelerates the selection of C. canephora plants with desirable characteristics and represents a novel approach for the focused breeding of crops.
... For example, carbohydrates and free sugars suffer pyrolysis, thermal and Maillard (with proteins and amino acids) reactions generate aroma precursors such as furanes, carboxylic acids, pyridines, pyrroles, pyrazines, thiazoles and ketones. Ferulic, caffeic and quinic acids from chlorogenic acids were degraded to produce phenols, and lipids through oxidation were transformed to alcohols, ketones and aldehydes [2,[43][44][45][46]. Interestingly, we detected a high number of lipids influencing the sensory attributes of coffee beverage. ...
Article
Full-text available
Genetic improvement of coffee plants represents a great challenge for breeders. Conventional breeding takes a too long time for responding timely to market demands, climatic variations and new biological threads. The correlation of genetic markers with the plant phenotype and final product quality is usually poor. Additionally, the creation and use of genetically modified organisms (GMOs) are often legally restricted and rejected by customers that demand natural products. Therefore, we developed a non-targeted metabolomics approach to accelerate conventional breeding. Our main idea was to identify highly heritable metabolites in Coffea canephora seedlings, which are linked to coffee cup quality. We employed a maternal half-sibs approach to estimate the metabolites heritability in open-pollinated plants in both leaves and fruits at an early plant development stage. We evaluated the cup quality of roasted beans and correlated highly heritable metabolites with sensory quality traits of the coffee beverage. Our results provide new insights about the heritability of metabolites of C. canephora plants. Furthermore, we found strong correlations between highly heritable metabolites and sensory traits of coffee beverage. We revealed metabolites that serve as predictive metabolite markers at an early development stage of coffee plants. Informed decisions can be made on plants of six months old, compared to 3.5 to 5 years using conventional selection methods. The metabolome-wide association study (MWAS) drastically accelerates the selection of C. canephora plants with desirable characteristics and represents a novel approach for the focused breeding of crops.
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This study investigated the non-volatile and volatile compounds in samples of cold brew (CB) coffee, coffee from a coffee shop (CS), ready-to-drink (RTD) coffee, and brewed coffee from a coffee maker (CM). The volatile compounds were identified using headspace solid-phase microextraction with gas chromatography-mass spectrometry, and the samples were treated with high-performance liquid chromatography for the quantification of caffeine, chlorogenic acid, and trigonelline. The results indicate that RTD coffee had the lowest amounts of non-volatile compounds. A total of 36 volatile compounds were semi-quantified; the contents of most volatile compounds in CS and Folgers samples were higher than those in CB and CM samples. The contents of 25 volatile compounds in the CM sample were higher than those in the CB sample. The consumer and instrumental data show that the bitterness intensity was correlated with pyrazines, pyrroles, and guaiacols, whereas the coffeeID intensity was correlated with phenols. Semi-quantification and principal component analysis results show that the extraction method and temperature could influence the volatile compound profiles.
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em>Pulping and fermentation of coffee cherry determine the quality of green beans and coffee flavors. Delay in pulping will cause the slime stick to the hull skin hence decreasing the bean quality and flavor. The objective of this study was to examine the effect of soaking before pulping and fermentation time to the color of coffee hull skin and the cup quality. The research was carried out at the experimental station of Indonesian Coffee and Cocoa Research Institute in Malang Regency (ICCRI) and ICCRI laboratory in Jember Regency from July 2018 to January 2019. Experiments used factorial completely randomized design. The first factor was cherry soaking duration (0, 24, 48, and 72 hours) and the second factor was fermentation duration (0, 24, and 48 hours) and then combined into 12 treatments, with three replications. Ten kilograms of coffee cherries were soaked prior to pulping then fermented in a plastic bag and added with Lactobacillus casei 2,5 x 10<sup>7</sup> cfu/ml as starter. Parameters observed were color of hull skin ( L value , a* , dan b*) and the cup quality. The results showed that soaking the cherry decreased the green beans quality which is indicated by less brightness (L), high a* value, and decreasing b* value of hull skin color. While the fermentation treatment can increase the value of L, decrease the a* value, and increase the b* value. The interaction of treatment of soaking and fermentation time significantly affected the lightnessl a* and b* value. Soaking and fermentation treatments did not significantly affect to the flavor, salt/acid, balance, and total score of coffee flavor. Soaking is not recommended for more than 48 hours and fermentation should be carried out 48 hours.</em
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