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Chapter 2. A Review of Coffee Quality Assessment Based on Sensory Evaluation and Advanced Analytical Techniques

  • Federal Technological University of Paraná (UTFPR) - Brazil
  • Technological Federal University of Paraná (UTFPR) - Campo Mourão - PR - Brazil


Coffee is a valuable agricultural product, popular and appreciated worldwide due to its unique flavor and aroma. As coffee has an important economic participation in the food sector, this plant-based product needs to be constantly analyzed to ensure its quality and safety. Over decades of research, hundreds of studies have concerned with investigating coffee quality. In particular, the most important methods for analyzing the cup quality of the coffee are taken from the Specialty Coffee Association (SCA) and from the Brazilian legislation, where SCA is considered the most appropriate. Although these methods have been widely used in the coffee industry, from a sensory perspective, these methods face challenges related to their subjectivity, reproducibility, time requirement and poor correlations with descriptive sensory analysis. Therefore, different approaches based on chemical analysis, chromatographic techniques, vibrational and molecular spectroscopies have been proposed to assess the coffee quality and overcome challenges in the various sectors of coffee industry. In this context, this review reports and discusses the literature related to sensory evaluation and analytical techniques applied to assess coffees of different cup qualities. In addition, new possibilities for real-time and in situ analyses of coffee quality using portable/handheld equipment will be discussed. The description of studies on coffee quality is beyond the scope of this review. However, the authors briefly covered the main examples to give the reader an idea about of the state of the art of coffee quality.
In: Innovations in Coffee Quality ISBN: 978-1-53618-223-1
Editors: Daneysa L. Kalschne et al. © 2020 Nova Science Publishers, Inc.
Chapter 2
Michel Rocha Baqueta1, Nicola Caporaso2,3,
Aline Coqueiro4 and Patrícia Valderrama1,*
1Universidade Tecnológica Federal do Paraná, Campo Mourão,
Paraná, Brazil
2Division of Food Sciences, School of Biosciences,
University of Nottingham, Leicestershire, UK
3Department of Agricultural Sciences,
University of Naples Federico II, Portici (NA), Italy
4Universidade Tecnológica Federal do Paraná, Ponta Grossa,
Paraná, Brazil
* Corresponding Author’s Email:
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Michel Rocha Baqueta, Nicola Caporaso, Aline Coqueiro et al.
Coffee is a valuable agricultural product, popular and appreciated
worldwide due to its unique flavor and aroma. As coffee has an important
economic participation in the food sector, this plant-based product needs
to be constantly analyzed to ensure its quality and safety. Over decades of
research, hundreds of studies have concerned with investigating coffee
quality. In particular, the most important methods for analyzing the cup
quality of coffee are taken from the Specialty Coffee Association (SCA)
and from the Brazilian legislation, where SCA is considered the most
appropriate. Although these methods have been widely used in the coffee
industry, from a sensory perspective, these methods face challenges related
to their subjectivity, reproducibility, time requirement and poor
correlations with descriptive sensory analysis. Therefore, different
approaches based on chemical analysis, chromatographic techniques,
vibrational and molecular spectroscopies have been proposed to assess the
coffee quality and overcome challenges in the various sectors of the coffee
industry. In this context, this review reports and discusses the literature
related to sensory evaluation and analytical techniques applied to assess
coffees of different cup qualities. In addition, new possibilities for real-
time and in situ analyses of coffee quality using portable/handheld
equipment will be discussed. The description of studies on coffee quality
is beyond the scope of this review. However, the authors briefly describe
the main examples to provide insight into the state of the art of coffee
Keywords: coffee cup quality, cupping, expert coffee grading, analytical
technologies, innovative analytical methods
Coffee is a valuable agricultural product, popular and appreciated
worldwide due to its unique flavor and aroma. As one of the most consumed
beverages in the world, coffee has also nutritional and protective properties,
in addition to being linked to emotional well-being (Poole et al. 2017; Uman
et al. 2016). After oil, coffee is the largest plant-based product legally traded
(Uman et al. 2016), with a global production of over 169 million 60-kg bags
in 2019, where Brazil is highlighted as the largest producer (International
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Coffee Organization ICO 2019). Other producers, such as Vietnam,
Colombia, Indonesia, and Ethiopia, form the global coffee production chain
(ICO 2019; Jeszka-Skowron et al. 2017). In relation to consumption, the
United States of America, Europe, and Brazil lead this market and the
demand for coffee is growing worldwide (ICO 2019; Evangelista et al.
Coffee has a high value in the world trade and important economic
participation in the food sector, which created a specific segment for its
quality control (Dias et al. 2018). Due to this, coffee needs to be constantly
analyzed to ensure its quality and safety (Monteiro et al. 2018). Over
decades of research, hundreds of studies have concerned to investigate
coffee quality. These include cupping methods, chemical analysis,
chromatographic techniques, vibrational and molecular spectroscopies
(Wang, Lim, and Fu, 2020; Burns, Tweed, and Walker, 2017; Pereira et al.
2019; Barbin et al. 2014; Jeszka-Skowron, Zgoła-Grześkowiak, and
Grześkowiak, 2014). In this context, this review reports and discusses the
literature related to sensory evaluation and analytical techniques applied to
assess coffees of different cup qualities. In addition, new possibilities for
real-time and in situ analyses of coffee quality using portable/handheld
equipment will be discussed. The description of studies on coffee quality is
beyond the scope of this review. However, the authors briefly present the
main examples to update the reader on the state the art of coffee quality.
Green coffee beans are generally used in medicinal and dietary
preparations, while roasted coffee beans are mainly used in beverage
preparations (Uman et al. 2016). However, many variables are responsible
for aroma, flavor, and overall quality of the coffee (Angeloni et al. 2019).
Quality is an important aspect for the current coffee industry to satisfy the
demands of the coffee consumer market (Barbin et al. 2014).
The International Organization for Standardization (ISO) has officially
defined the term quality as the extent to which a group of intrinsic
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features satisfies the requirements, where requirement means need or
expectation, which may be explicit, generally implicit, or binding (ISO
2000). However, quality can take on different meanings for consumers,
producers, and regulatory organizations (Ribeiro, Ferreira, and Salva 2011).
This means the quality can be very subjective and vary according to the
object in question, especially for the coffee sector.
The quality of coffee beans has a direct impact on the valorization of the
beverage, being a decisive factor in the definition of its price. However, the
coffee bean quality results from several intrinsic and extrinsic factors, such
as the altitude and soil composition of coffee plantation, botanical species,
variety, cultivation system, irrigation, geographical origin, seasonal
conditions, post-harvest processing methods (washed, pulped natural,
natural, fermentation conditions) and chemical changes that occur during
this stage, appearance and shape of the bean, presence of defective beans
and foreign matters, the chemical composition of green coffee beans, cup
quality profile and preparation method (Belchior et al. 2019; Toci, and
Boldrin 2018; Craig et al. 2018; Monteiro et al. 2018; Tolessa et al. 2016;
Ribeiro, Ferreira, and Salva 2011). Therefore, research on coffee quality
must consider a range of variables that directly affect its final quality.
There are two different species of coffee grown with global economic
importance: Coffea arabica L. and Coffea canephora Pierre ex A. Froehner.
Both species belong to the same family (Rubiaceae), and genus (Coffea)
(Illy and Viani 2005), but have distinct physical, chemical and sensory
properties (Davis et al. 2011). In general, beverages from C. arabica L.
(commonly known as Arabica) have a higher price, lower caffeine content,
tend to have more fruity notes and intense flavor, with wider variations in
the body and acidity (Dias et al. 2018). On the other hand, the beverages
from C. canephora Pierre ex A. Froehner (commonly known as Robusta or
Conilon) are generally neutral and unflavored, lower priced, higher in
caffeine and more bitter (Craig et al. 2018; Davis et al. 2011). In industry,
the mixing of two species is used to create different sensory profiles,
standardize quality and adjust prices (Dias et al. 2018).
The coffee beverage profile is linked to the chemical characteristics of
the bean and the conditions in which it is grown. Green coffee bean does not
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present very attractive characteristics in the sensory sense, as the coffee
beans acquire their unique flavor and aroma during the roasting process.
Regardless of the processing method, coffee beans are roasted to develop
the characteristic profile of roasted coffee and produce a beverage that is
pleasant to the palate (Uman et al. 2016; Esquivel and Jiménez 2012).
Roasting is one of the most important steps during coffee production. The
main chemical reactions occur during this process, forming various
compounds that characterize the beverage. Although the chemical
mechanisms that occur during the roasting process have an intense impact
on the final quality of the coffee, they are complex and are not yet fully
understood. Decades of scientific studies explore the complex composition
of the aroma of roasted coffee and, in this extensive period, hundreds of
volatile compounds have been identified (Pereira et al. 2019).
Coffee bean is chemically complex and both green and roasted coffee
beans contains a wide variety of chemical compounds, which may react and
interact amongst themselves during the roasting process, resulting in very
diverse end products (Ribeiro, Ferreira, and Salva 2011). The influence of
coffee chemical compounds, for example, chlorogenic acids, carbohydrates,
proteins, trigonelline and caffeine on the final quality of the beverage has
already been established in the literature (Bressanello et al. 2017; Ribeiro,
Ferreira, and Salva 2011). In parallel, some of these coffee compounds are
considered bioactive substances, where some have potentially psychoactive,
anti-inflammatory, antifibrotic or anticancer effects, in addition to being
responsible for characteristics found in the coffee beverage, such as body,
aroma, and acidity (Poole et al., 2017).
2.1. Coffee Classification by Cup Quality
In the coffee industry, several methods are used to classify coffee at
different stages of production (Ribeiro et al. 2009). Among them, expert
coffee grading or cupping, is the most important tool for the assessment of
green coffee quality. Given its wide application worldwide, it is widely used
for routine analysis of the final quality of coffee in coffee industries (Craig
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et al. 2018; Di Donfrancesco, Guzman, and Chambers 2014; Feria-Morales
2002). This methodology is based on the sensory perception of professional
coffee tasters, also called ‘cuppers’, to evaluate and score individual coffee
attributes. These cuppers are usually trained to assess any change in the
characteristics of the product (Feria-Morales 2002). Ideally, the cupping
consists of a team of cuppers who tastes three to ten cups of the same coffee
sample, prepared according to standardized conditions of temperature,
contact time (extraction), water/coffee ratio, water quality, and brewing
method (Specialty Coffee Association SCA 2009). The cupping score
sheet includes important attributes of coffee quality, ranging from 0 to 10.
In the current version, fragrance/aroma, flavor, aftertaste, acidity, body,
balance, uniformity, clean cup, sweetness, defects, and overall quality are
the evaluated attributes. However, these recommendations are often not
followed, especially when it comes to industrial scale, so it is common to
find disagreements on this subject in research reports and during routine
analysis in the coffee industries.
Sensory assessment is a crucial tool for determining the quality of coffee
beverage (Giacalone et al. 2019). Often, cupping is more anchored in the
tradition of coffee classification, rather than being an adequate sensory
analysis. The cuppers may be good at overall quality measures but not adept
at measuring specific sensory qualities (Di Donfrancesco, Guzman, and
Chambers 2019; Di Donfrancesco, Guzman, and Chambers 2014). Despite
its wide application, from a scientific point of view, current cupping
procedures can be criticized for some reasons. Firstly, while the methods of
sensory science depend on a large group of assessors (sensory panel) to
guarantee robust results, the coffee industry depends mainly on a few expert
tasters with years of experience. Generally, only one or two tasters are
responsible for evaluating the quality of many coffee samples, sometimes
tasting more than 200 cups a day. Furthermore, tasting is often not blind,
which means that the expert cuppers usually have information about the
coffee variety and the supplier. Finally, until recently, there was no
consensus on sensory vocabulary or the use of specific scales, which still
vary substantially depending on the country of origin of the coffee and even
the company conducting the cupping (Di Donfrancesco, Guzman, and
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Chambers 2014; Feria-Morales 2002). Previous studies have verified a poor
correlation between the results of cupping and Descriptive Sensory Analysis
(DSA) with trained panelists, leading the authors to conclude that these two
approaches are not interchangeable. In addition, cupping scores are either
not repeatable from different groups of cuppers or are unrelated to consumer
acceptance of coffee (Worku, Duchateau, and Boeckx 2016; Giacalone et al.
2016; Di Donfrancesco, Guzman, and Chambers 2014).
It is evident that there is an inherent complexity in the application of the
cupping method, as this procedure has serious flaws. This includes the lack
of definition of the attributes to be scored and the mixture of subjective and
objective attributes in the same evaluation. In addition, cupping methods are
time-consuming, laborious, expensive, and require trained cupper experts
that take years to acquired experience. Become an expert depending on
extensive training, needs the good sensory ability to perceive specific
attributes, and relies on very few data (Giacalone et al. 2019; Craig et al.
2018; Toledo et al. 2016; Feria-Morales 2002). Another notable difference
from the sensory evaluation is that the quality judgments in cupping combine
an overall quality scale with diagnostic information about defects, whereas,
in the conventional sensory evaluation these two functions (descriptive and
consumer) would be typically separated in two distinct tests with different
responses (Giacalone et al. 2019). Suppose that the opinion of one or some
experts can effectively predict consumer preferences is questionable. In fact,
particularly for coffee, quality assessments carried out by coffee experts do
not necessarily correspond to consumer preferences (Giacalone et al. 2016).
A final problematic aspect of the cupping protocols is the use of holistic
quality attributes, rather than clearly defined sensory properties (Giacalone
et al. 2019).
2.2. Coffee Classification According to SCA
Many systems are available to assess the cup coffee quality, including
detailed guidelines for Arabica and Robusta/Conilon classification. The
quality profiles of coffee vary according to the producing country and must
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be considered specific for each market source. As a consequence, coffee
classification follows country-specific guidelines (Tolessa et al. 2016).
Currently, the most appropriate cupping method is based on SCA protocols.
Over the years, the Coffee Cuppers Handbook has published a list of
protocols and standards that have become benchmarks for the coffee trade
between the US and Brazil. Among these documents, the Cupping Specialty
Coffee protocol and the Grading Green Coffee protocol received special
attention because they are useful in classifying coffee by experts (Lingle
2011; SCA 2009).
The SCA provides standardized coffee grading protocols based on the
cup quality for different purposes, such as different tests for the grading of
Arabica and Robusta/Conilon coffees. Cupping protocols of the SCA were
built by experts in the coffee trade and researches and are widely used to
classify coffees with different cup qualities and specialty grade coffees.
Specialty grade coffees are those whose cultivation, pre-processing and
processing (including or not the fermentation step) are carefully carried out
under suitable conditions, resulting in a final coffee beverage of excellent
quality, with exceptional flavor, aroma, and representative of specialty
coffee (Lingle 2011; SCA 2009).
The cupping protocols provided by the SCA are methods to analyze and
compare coffee beans of different cup qualities and are widely used to
analyze and classify specialty grade coffees. The relationship between
defective coffee beans and the specialty grade coffees as follows for SCA:
no primary defects are allowed (full black, full sour, pod/cherry, medium or
large stones and sticks) on specialty grade coffees; these coffees should
contain no more than 5 full secondary defects in 300 grams of coffee
(parchment, husk, broken, insect damage, small stones and sticks, partial
black or sour, and water damage). In addition, specialty grade coffee must
exceed eighty points in cupping, where the sum of the individual scores of
all attributes is the final score, which represents the overall quality of the
coffee (Lingle 2011; Toci and Boldrin 2018). Therefore, specialty coffee has
high-quality beans based on expert testing, but may differ from consumer
preference. A more meaningful definition for quality would be to say that it
is what consumers like, even when there is a discrepancy between
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preferences. In fact, the scores of cuppers correlate very poorly with
consumer preferences (Giacalone et al. 2016). In addition, worldwide, the
production of specialty grade coffee is restricted, which means that most of
the coffee consumed is of regular quality and consumers, in general, are
more accustomed with to quality grade.
Coffea canephora
C. canephora, known as Conilon or Robusta, accounts for about 40% of
global coffee production (ICO 2019; Rocha et al. 2013). However, many
times, this coffee does not receive the same care and attention during its
production and processing phases as it is made for Arabica coffee and this
directly affects its quality. C. canephora is often neglected due to its
traditional inferior quality in cupping tests, and usually intended only for the
manufacture of instant coffee (Fiorott and Sturm 2015). Therefore, this
coffee has a lower price on the international market compared to Arabica
coffee. The chemical differences between these species were reviewed in
detail by Illy and Viani (2005). According to these authors, Arabica has
lower levels of caffeine, amino acids, and chlorogenic acids compared to
Robusta, with high oil content. The reduced content of chlorogenic acids in
Arabica favors the final quality of the cup and contributes to the low
astringent notes in the brew. In addition, the differences of cup quality
between Arabica and Robusta, especially in espresso, may also be explained
by the level of the oil fraction, as it is known that many aromatic volatile
compounds are dissolved in oil droplets and released during brewing.
The poor reputation of C. canephora and its inferior quality are a result
of its cultivation system, processing method and the presence of hundreds of
defects that, consequently, depreciates its final quality and price, rather than
the quality inherent to the species (Fiorott and Sturm 2015; Uganda Coffee
Development Authority UCDA 2010). In this perspective, its cup quality
is not a priority and is questionable. However, this unfavorable scenario has
been changed. An increasing improvement in cup quality of C. canephora
has been observed with nuances that surprise and please several specialists
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and consumers around the world (Fiorott and Sturm 2015). With a
significant improvement in its quality, world organizations such as the
Uganda Coffee Development Authority (UCDA) and Coffee Quality
Institute (CQI), with help of coffee professionals, are trying to change the
way C. canephora is seen. Those organizations, incorporating information
from the ICO and recommendations based on practices used for the
differentiation of Arabica coffee by the SCA, developed in 2010 the first
protocol that brings together standards and procedures that define fine
Robusta coffee, a class without defects equivalent to specialty Arabica, in
which the coffees present unique flavor and aroma, resulting from a
combination of varietal genetics and microclimate of origin, accentuated by
the best practices of cultivation and processing (Fiorott and Sturm 2015;
UCDA 2010). Although it has received the denomination related to Robusta
coffee, this protocol was developed to evaluate the Robusta or Conilon fine
(UCDA, 2010). Following a strict quality control protocol during cultivation
and processing, which led to worldwide recognition, the fine Robusta coffee
entered the scenario of high-quality coffee as a new market segment
following a trend of consumer behavior, consequently increasing its price,
which today is similar to specialty Arabica coffee (Fiorott Sturm, 2015).
With Robusta protocol, the quality of C. canephora beverages can be
assessed by analyzing several sensory attributes, such as fragrance/aroma,
flavor, aftertaste, salt/acid aspect ratio, bitter/sweet aspect ratio, mouthfeel,
balance, uniform cup, clean cup, and overall attributes. Similar to the
Arabica coffee assessment, the average scores of all attributes generates a
final score used to classify a beverage according to its quality (Souza et al.,
2018; Fiorott and Sturm, 2015; UCDA, 2010).
2.4. Brazilian Legislation for Coffee Classification
The Brazilian Official Classification (Classificação Oficial Brasileira
COB) evaluates green coffee quality based on physicochemical and sensory
parameters. This system has become the main reference for national and
international marketing of green coffee and traders still use it to grade green
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coffee and establish prices. In Brazil, Arabica coffee beans are classified into
seven categories: strictly soft, soft, barely soft, hard, rioysh, rio and rio zona,
by COB parameters, while Robusta coffee beans are classified into four
categories: excellent, good, regular and abnormal (which bears a non-
characteristic flavor of the product) (Brazil 2003).
These categories differ from sensory attributes. Strictly soft coffee tastes
very mild, slightly sweet, and slightly acidic. Soft coffee has a mild and
slightly sweet taste. Barely soft coffee has a mild taste but presents slight
astringency. The hard coffee has an acidic, astringent, rough and without
sweetness taste, presenting a full-bodied and pleasant beverage. Rioysh
coffee has a mild taste typical of iodoform or phenic acid and rio coffee is
considered characteristic for its unpleasant, typical and pronounced taste,
similar to iodoform or phenic acid. Finally, a rio zona coffee has a very
pronounced taste and aroma of iodoform or phenic acid (Farah et al. 2006).
In addition to assessing coffee based on cup quality, the Brazilian
classification includes two other assessments: the number of defective beans
and the sieve test. When assessing defects, defective beans and foreign
matter are counted from a sample of 300 g of green coffee. Defective beans
are visually identified as black, fermented, brown, immature, damaged or
insect-attacked, broken, and foreign matter that may be husks, twigs, and
stones (Franca et al. 2005). In the sieve classification, the beans are separated
by shape and there are two ways: oblong or flattened. Oblong
represents a coffee with inadequate development, where only one seed per
fruit has developed occupying the space of the other seed, showing a
rounded and longer shape. The flattened coffee is related to beans with
proper development, containing two seeds in the fruit. In this classification,
the beans are separated by sieves that retain the beans depending on their
Lowe-quality coffees, such as rioysh and rio, generally have a higher
number of defects compared to high-quality coffees, such as soft and hard
coffee (Franca et al. 2005). Campanha, Dias and Benassi (2010) related the
levels of kahweol and cafestol (p <0.05) with the number of defects in the
beans and did not report significant differences in the levels of these
compounds when comparing samples of defective and non-defective beans.
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Despite the increasing use of SCA's standardized protocols to assess the
coffee cup quality, Brazil still uses its own inspection methods for this
purpose (Ribeiro et al. 2018; Belchior et al. 2019).
Different analytical methods and approaches have been investigated to
objectively measure the quality characteristics of coffee. Several studies that
have addressed this topic by analyzing coffees of different qualities will be
shown below.
Robusta coffee is generally associated with lower sensory quality, but it
still has the potential to be improved using proper cultivation and an
adequate processing. As an example, Mendes et al. (2001) optimized the
Robusta coffee roasting process and correlated the sensory responses
obtained by trained tasters with the colorimetric measurements of roasted
and ground coffee. After optimizing the roasting process, the beverage was
classified as light in flavor, with low acidity and fair to the good body, which
results in a good quality beverage. The results showed that Robusta beans
roasted at an ideal temperature had high scores in terms of flavor and aroma.
The authors concluded that the optimization of Robusta coffee roasting has
a high potential to improve its sensory quality. A recently published study
showed the distinction between varieties of C. canephora (Souza et al.
2018). The results showed that the varieties Conilon and Robusta differ
significantly in nuances and sensory attributes. Another recent paper also
showed how to enhance the aroma of Robusta coffee (Liu et al. 2019).
Through modification of green coffee flavor precursors by sugar addition
(glucose, fructose, and sucrose) at different levels, the authors verified that
their treatments increased the similarity of Robusta to Arabica and that
aroma of treated Robusta coffee was more stable than Arabica. The optimum
treatment was 15 g of coffee per 100 g of fructose. From an industrial point
of view, these results encourage the production of coffee Robusta/Conilon
and recognition of its quality showing new possibilities by processing
modifications and good perspectives for the future market.
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The volatile compounds in coffee vary according to their species, cup
quality, and processing methods. Variations in the roasting process are
studied to verify its influence on coffee and its composition. Using a gas
chromatography approach coupled with mass spectrometry (GCMS),
Nascimento, Morais, and Rocha (2003) studied the influence of different
roasting conditions (light, medium, and dark) on the volatile composition of
two coffee beverage/brew qualities: gourmet (specialty coffee) and soft. In
their studies, it was pointed out that the type of roasting has a great influence
on the formation of produced volatiles. However, no significant difference
was found for volatile compounds among the investigated coffees. Despite
this, it was observed that the volatiles and their concentrations in roasted
coffee in medium and dark degrees were similar, while the roasted beans in
light degree showed a subtle difference in them.
Franca, Mendonça, and Oliveira (2005) used some physical and
chemical parameters to evaluate green and roasted coffees with different cup
qualities: soft, hard, rioysh and rio. The results obtained in the study of green
coffee beans showed that the density, volume, and protein levels, were
higher in soft coffee (higher quality) compared to rio coffee. The rio coffee
sample had a lower lipid content, probably associated with the presence of
defective beans that reduce the cup quality. Titratable acidity increased and
pH levels decreased as cup quality decreased, probably due to the effect of
defective beans subjected to fermentation (sour beans). After roasting, the
rio coffee sample showed higher density and trigonelline levels, indicating
that it was not roasted to the same degree as the other samples.
In a different approach, Monteiro et al. (2005) applied time-intensity
analysis to evaluate sensory attributes of soft, hard and rio coffees submitted
to different roasting processes (light, express and dark). Using traditional
statistical and exploratory analyses, Principal Component Analysis - PCA,
all dark roasted coffees had higher maximum intensity and duration of the
incentive for bitter taste and burnt flavor, while the opposite was observed
for lightly roasted samples; the rio/express sample was the one with the
highest intensity for the fermented flavor. The rio coffee roasted at express
degree was the one with the highest intensity of fermented flavor, being
defined as of lower quality and unpleasant taste. The sample of soft coffee
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at express roasting degree showed the lowest intensity of fermented flavor
since they are considered beans that result in better cup quality brews.
Coffee quality is often measured by a single cupping method and studies
have been conducted to find correlations between cup quality and chemical
compounds. Farah et al. (2006) investigated correlations between the cup
quality of green and roasted coffees, with brews classified as soft, hard,
rioysh, rio and rio zona. The concentrations of sucrose, caffeine, trigonelline
and chlorogenic acids were determined by High-Performance Liquid
Chromatography (HPLC). In general, the authors reported that the chemical
composition evaluated is correlated with the cup quality. Trigonelline and
3,4-dicaffeoylquinic acid were strongly correlated with high cup quality and
caffeine was slightly associated with good cup quality. On the other hand,
the presence of defective beans can increase the levels of caffeoylquinic
acids (predominantly 5-caffeoylquinic acid), feruloylquinic acids, and their
oxidation products have been associated with the low cup quality. The
results obtained were promising since good correlations were found between
the cup quality and the chemical compounds of green and light roasted
coffee. These findings are useful for coffee professionals and for the purpose
of routine analysis and inspection of coffee quality control.
Alves et al. (2007) also used chemical parameters to evaluate soft, hard,
rioysh and rio coffees originally from different geographical origins in
Brazil. Some parameters such as proteins, total phenolics, chlorogenic acids,
caffeine, and trigonelline were significantly important in discriminating the
geographical origin and the cup quality. However, no significant difference
was found in terms of pH, soluble solids and caffeic acid. In addition,
variations in the protein content were observed in relation to the cup quality:
from soft to hard coffee, the protein content increased, decreasing in rioysh
coffee, and rising again in rio coffee. The total phenolic content was higher
in soft coffee, while the chlorogenic acids and trigonelline contents
decreased as the cup quality decreased. Caffeine levels were slightly higher
in samples of soft and hard coffees from the Cerrado region. These
findings were supported by Franca, Mendonça, and Oliveira (2005), who
also reported higher levels of protein and caffeine in soft coffees and meet
the observations of Farah et al. (2006).
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Dal Molin et al. (2008) evaluated the effects of climatic conditions and
cultivation practices on the quality of the coffee and its cup quality. The
authors concluded that monitoring climatic conditions in conjunction with
appropriate agricultural practices can be an attractive alternative for
producing coffees with better cup quality and with great potential for
obtaining high-quality coffees. Eighty-six percent of the investigated coffees
were classified as soft or hard versus 14% of rioysh or rio. From a general
point of view, the results extend the frontier in the production of coffee with
high cup quality.
In a pioneering study, over half a century ago, Amorim and Silva (1968)
found that soft coffee had greater polyphenol oxidase (PFO) activity than a
rio coffee. These previous findings were confirmed by da Silva et al. (2009).
In their results, the authors used chemical and sensory properties for
discriminating coffees produced in different localities of the State of Minas
Gerais, Brazil. The authors reported that the cupping method did not indicate
a significant difference in the quality of the coffees produced in the different
regions studied: all coffees were classified by the cuppers as a hard beverage.
However, the total titratable acidity, color index, and PFO allowed
differentiating more precisely the quality of the coffee. The coffees produced
in the north of Minas Gerais presented higher PFO activity, color index, and
lower acidity than the lower quality coffees produced in Vale do
Jequitinhonha and Mucuri regions.
Kenyan Arabica coffee genotypes were also evaluated to find
correlations between sensory qualities and physical characteristics of coffee
beans (Kathurima et al. 2009). Significant differences were found among the
evaluated genotypes, but no significant correlation was found between
sensory properties and physical characteristics of coffee beans. These results
suggested that the use of the physical aspects of green beans in selecting a
beverage with better cup quality is impracticable.
Ribeiro et al. (2010) explored the differentiation of coffees with
different cup qualities by sensory properties, such as flavor, aroma, and
overall quality, and using chromatographic profiles obtained from GCMS
analysis. Twenty-four samples were classified as excellent overall quality,
22 as excellent aroma, 17 as soft, 12 as poor quality, 11 as weak aroma, and
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10 as rioysh or rio. Despite the dozens of compounds identified, multivariate
analysis based on PCA showed that 54 were considered as possible markers
to track their quality. Among these compounds, pyrrole, 1-methyl-pyrrole,
cyclopentanone, dihydro-2-methyl-3-furanone, furfural, 2-ethyl-5-methyl-
pyrazine, 2-ethenyl-n-methyl-pyrazine, 5-methyl-2-propionyl-furan were
considered markers of the coffee quality discrimination, considering its
aroma, flavor, and overall quality. Most of these volatiles when in high
concentration were associated with an increase in the coffee cup quality.
However, the opposite was observed in the presence of compounds such as
pyrrole, 1-methyl-pyrrole, and cyclopentanone in high concentrations,
which had a negative effect on the coffee beverage, resulting in a decrease
of its cup quality.
In a different approach, Toci et al. (2013) monitored changes in the
composition of triacylglycerols and free fatty acids (FFA) during the storage
of strictly soft roasted coffee in two degrees of color (light-medium and
dark-medium) for six months under temperature variations (5 °C and 25 °C)
and atmosphere (air or N2). The results showed that the oxidation of free
fatty acids during storage is a phenomenon to be taken into account. The
main changes resulting from these treatments were apparently in the
composition of the triacylglycerols. For light-medium and dark-medium
coffees, reductions of 20% and 13% in the FFA content was observed,
respectively, after 3 months of storage, which suggests oxidative processes.
Both N2 atmosphere and storage at 5 ºC contributed to a lower loss of FFA.
Ribeiro et al. (2014) investigated differences in chemical and sensory
parameters of blends prepared with different proportions of Arabica and
Robusta coffees. Arabica beans were classified as soft and Robusta as a good
beverage in the cupping method by the SCA protocol. The observed
differences showed that as the proportion of Robusta coffee increased, all
chemical and sensory attributes changed significantly. Blends with higher
proportions of Robusta beans negatively affected sensory attributes such as
fragrance, aroma, and acidity, and changed the bitterness and body.
Furthermore, it was noted an increase in the proportion of Robusta beans in
the blend is related to an increase in the levels of caffeine, soluble solids,
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and polyphenols and a decrease in the levels of ethereal extract and total and
non-reducing sugars.
Solid-phase microextraction (SPME) coupled with GCMS analysis
also proved to be a promising strategy for characterizing volatile compounds
in coffee beans and coffee beverages (Caporaso et al. 2014; Caporaso et al.
2018a). Caporaso et al. (2018a) reported the variability of volatile
compounds from a single roasted coffee bean from different geographical
and botanical origins (Arabica and Robusta coffees). It has been shown that
when using identical roasting conditions a large variation in the relative
concentration of volatile compounds with a significance odor can be found
between different origins (inter-batch variation) or within the same sample
(intra-batch variation). This factor must be considered to improve the final
quality of the coffees. Caporaso et al. (2014) reported that the volatile profile
of coffee brews changed significantly, depending on the type of coffee
brewing procedures applied, e.g., comparing espresso, filtered (Americano),
moka (a classic Italian-making process), and Neapolitan coffee, which is
based on percolation using a different coffee machine.
The above-mentioned analytical strategies (cupping, physicochemical,
and chromatographic methods) faces challenges for the current coffee
analysis. In addition, most of these methods tend to require sophisticated
analytical equipment and qualified operators; they are also time-consuming
and require the purchase and disposal of chemical reagents. In addition, the
cupping method is subjective and therefore uncertain. For all these reasons,
there is a continuous demand for new, fast, non-destructive, cheaper, and
green methods for the direct measurement of coffee quality. Spectroscopic
techniques, including near-infrared (NIR), mid-infrared (MIR) and nuclear
magnetic resonance (NMR) spectroscopy, all associated with an appropriate
chemometric strategy, have been examined to assess their suitability for
determining quality, geographical origin, routine analysis and inspection
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purposes of coffee. Therefore, advances in analytical instrumentation for
coffee quality assessment will also be presented.
Vibrational spectroscopy in the infrared region is becoming a more
attractive analytical technique for measuring quality parameters in coffee
(Barbin et al. 2014). In this case, most applications have focused on a larger
use of the NIR than the MIR spectroscopy, possibly associated with
instrument availability, simplicity, and speed in the analysis of solid samples
such as roasted and ground coffee. The main advantages of NIR
spectroscopy are not extensive sample preparation, direct solid sample
analysis, acquisition data is quick in the simultaneous determination of
several parameters substituting expensive and time-consuming reference
techniques and yet an eco-friendly alternative.
The NIR is widely used for qualitative and quantitative analysis of green
and roasted coffee. It was used to determine the geographical origin of green
coffee (Giraudo et al. 2019), to authenticate the geographical and farming
systems origins of roasted coffees (Monteiro et al. 2018), for monitoring the
degree of roasting (Catelani et al. 2018) and acidity during roasting process
(Catelani et al. 2016).
The NIR has also been used to determine the presence of defects in green
coffee (Santos et al. 2012). A multivariate calibration strategy based on
Partial Least Squares (PLS) regression was used to relate the NIR spectra to
the mass fraction of defective and non-defective beans. The authors
concluded that NIR is a good analytical tool to be used in the quantitative
assessment of green coffee with defects. Recently, Infrared-Photoacoustic
Spectroscopy (FTIR-PAS) was applied to roasted and ground coffee with
different amounts of specific defects (Dias et al. 2018). Successful
discrimination of the investigated coffees was found, and the Partial Least
Squares associated with Discriminant Analysis (PLS-DA) allowed to predict
the quantity/fraction and the nature of the defects in the blends. Subsequent
analyses using PCA revealed similarities between blends and the PLS-DA
model correctly classified all samples into four classes with 90% of success.
The evaluation of sensory properties is among the most important
aspects to determine the coffee quality and numerous studies have been
carried out in an attempt to find correlations between sensory qualities and
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emerging analytical techniques. Santos et al. (2012a and b) used NIR in
combination with multivariate chemometrics to discriminate commercial
coffee (traditional, gourmet and decaffeinated) and coffees with different
cup qualities (soft, hard, rioysh and rio). The plots defined by the first two
PCs of the two multivariate methods were enough to provide well-separated
groups corresponding to commercial coffees and coffees of different cup
qualities. The Soft Independent Modeling of Class Analogy (SIMCA)
applied on the NIR data allowed an excellent classification of the
investigated coffees since 95% of correct classification was obtained for
coffees of different cup qualities. For predicting commercial coffees, 90.8%
of correct classification was obtained. In the PLS-DA model, the coefficients
of determination were higher than 0.9 for coffees with different cup
qualities, with a prediction error lower than 5%. For commercial coffees, the
model presented a coefficient above 0.88 and an error value below 3.7%. In
conclusion, the NIR associated with SIMCA or PLS-DA can be a suitable
method for the differentiation of roasted coffees and powerful to replace
cupping methods.
Recently, the potential of MID spectroscopy to predict coffee cup
quality has been investigated (Craig et al. 2018). MID spectroscopy was able
to predict cup quality of Arabica coffees of different roasting degrees with
acceptable accuracy to be useful industrially. In addition, the PCA allowed
the separation of Arabica and Robusta coffees, while the PLS-DA, with
hierarchical strategies, showed two different levels of separation: in the first,
the coffees were classified as high or low quality, while the other separated
the samples according to cup quality. Concluding, MID spectroscopy and
chemometrics seem to be a promising method to obtain information about
the coffee cup quality, regardless of the roasting conditions.
Espresso coffee capsules were studied to find correlations between
sensory qualities and infrared spectroscopy data. In the first one, Belchior,
Franca, and Oliveira (2016) reported the use of Diffuse Reflectance Infrared
Fourier Transform Spectroscopy (DRIFTS) for discrimination between
roasted coffees with different sensory characteristics and roasting degrees.
Chemometric approaches made it possible to classify espresso coffees into
three groups: sugar browning, enzymatic, or dry distillation. The authors
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concluded that DRIFTS and generic descriptions of the intensity of some
sensory parameters provided by manufacturers in combination with PCA
and PLS-DA are interesting methods for examining espresso coffee capsules
with different sensory properties.
Recently, the same research group analyzed espresso coffees with
different sensory characteristics reported by a panel of coffee tasters
(Belchior et al. 2019) and assessed by Attenuated Total Reflectance Fourier
Transform Spectroscopy (ATR-FTIR). For the sensory analysis, the SCA
recommendations were respected to determine the quality of sensory
attributes, such as aroma, flavor, aftertaste, acidity, body, and overall
quality. Their results showed that the sensory analysis of espresso coffee,
together with the ATR-FTIR technique, were effective in distinguishing
between coffee samples and their sensory characteristics. The authors found
successful discrimination between espresso coffees according to their
descriptors of aroma and flavor using the PCA, while a large classification
was found in the PLS-DA built for each sensory attribute. In addition, the
authors showed a relationship between the chemical composition of coffees
and sensory qualities. Acidity was associated with the presence of carboxylic
acids, alcohols, and chlorogenic acid. Flavor, aftertaste, and body were
associated with the lipid composition, protein levels, trigonelline, caffeine,
carbohydrates, carboxylic acids, and chlorogenic acids. Aldehydes, esters,
ketones, and overall acids contributed to the description of the aroma
Nowadays, the food industry demands of alternative methods to ensure
the quality and safety of their products and processes. For this reason, the
emergence of techniques for real-time and in situ analyses both in the
industry and on the farm is increasingly common. In this context, new
possibilities for coffee industry and its professionals by using portable and
hand-held equipment such as miniaturized spectrometers and smartphone-
based image will be discussed. These techniques also are considered eco-
friendly alternatives because they comply with the recommendations of
green chemistry, and share the advantage of being portable, low cost, easy,
fast, and non-destructive compared to other reference techniques. In
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addition, these techniques require little or no processing or sample
In this context, portable spectrometers have been used to monitor coffee
quality characteristics. Correia et al. (2018) used a portable NIR to detect
adulteration of Arabica coffee with Robusta coffee, corn, and husks/sticks
at different roasting levels. The acquired microNIR spectra were treated
with PCA and PLS. The PCA applied to the NIR data showed a clear
separation between authentic and adulterated samples in both cases. Using
the PLS regression, a good sensitivity of the method to detect the adulterant
content in Arabica coffee was observed and the limits of detection and
quantification were below 8.7% for the blends of Arabica coffee containing
peels/sticks and corn. From the results, it was concluded that the portable
NIR applied to the qualitative and quantitative identification of coffee
adulterants is robust and could be an appropriate tool for monitoring the
authenticity of Arabica coffee.
Recently, Baqueta, Coqueiro, and Valderrama (2019) applied a
chemometric treatment (PLS regression) in microNIR spectra of Brazilian
coffee blends with different cup qualities to predict sensory attributes. Four
coffee blends with different cup qualities and roasting degrees were used:
hard/rioysh medium, hard/rioysh dark, rioysh/rio medium-dark, and
hard/Robusta light. A total of 217 samples were analyzed by cuppers of a
Brazilian coffee industry. The results of the sensory attributes that included
powder fragrance, drink aroma, acidity, bitterness, flavor, body, astringency,
residual flavor, and overall quality were successfully predicted by a
portable/handheld NIR. The obtained models showed a technological
potential for the evaluation of the sensory properties of coffee blends with
great quantitative viability. The models were accurate enough to be
recommended for real-time quality assessment and can be useful for the
coffee industry and for coffee professionals. Using a similar approach, the
same researchers also applied the portable NIR to monitor the quality
parameters (granulometry, moisture content, roasting degree and infusion
time) in an industrial system of coffee quality control. Using an appropriate
number of PLS factors, the models produced acceptable predictions
(Baqueta et al. 2020). Therefore, considering that real samples were
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analyzed in an industrial scale by these authors, it shows that portable NIR
could be safely used for real-time monitoring in the coffee industry.
Another recent study compared two NIR spectrometers for real-time
analysis of coffee matrices (Tugnolo et al. 2019). The authors measured the
potential of a benchtop spectrophotometer and a portable spectrophotometer
coupled with PLS models to predict moisture content on roasted coffee and
ground roasted coffee, and to predict also tap density, and powder
granulometry on ground roasted coffee. In general, the results obtained by
these authors indicated that there is no significant difference in robust terms
for prediction of these parameters between equipment studied.
A different promising portable instrument is the smartphone-based
image, but despite its contribution in other fields, its application has not yet
been reported for coffee. From an industrial point of view, computer vision
system provided by smartphone is a remarkably interesting technique for
future applications in coffee sector and might be an easy tool for coffee
professionals and coffee processing with several advantages (Baqueta et al.
As an alternative to benchtop and portable NIR and to smartphone-based
image, a new analytical technique like conventional NIR spectroscopy is the
Hyperspectral Imaging (HSI), which combines digital images and
spectroscopy. When detection is performed in the NIR range, it can provide
information about the main compounds in green and roasted coffee beans,
without the need for any preparation, quickly and non- destructively and
differentiating the beans individually. In a recent article, Caporaso et al.
(2018b) demonstrated the feasibility of using the NIR-HSI to evaluate the
moisture and lipid content in single green coffee beans, with potential
implications for the final quality of the coffee. In a subsequent experiment,
Caporaso et al. (2018c) demonstrated that this technique is also applicable
to the estimation of quality related chemical compounds found in lower
concentrations, such as caffeine and trigonelline, whereas for sucrose only a
rough estimate is possible due to its lower content.
In addition to these applications using infrared spectroscopy, NMR-
based metabolomics have been explored for coffee analysis. The
investigation by Ribeiro et al. (2017) used the NMR spectroscopy to
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authenticate strictly soft and soft coffees. Using adulterants such as corn,
coffee husks, barley, and soybean, it has been shown that NMR in
combination with chemometrics techniques was suitable to determine
adulterants in coffee samples and can be used as an efficient tool for
authenticity testing.
Recently, Toci et al. (2018) analyzed coffees classified as gourmet,
strictly soft, soft, rio zona and waste from different regions to trace their
geographical origin. Despite the complexity of data interpretation due to a
large number of compounds in coffee, the NMR spectra obtained showed
significant differences and allowed differentiation of coffees according to
the geographical origin, even with the proximity of some producers such as
São Paulo and Minas Gerais States that have similar climate and altitude.
In conclusion, it is worth noting that reference techniques are still widely
used in routine coffee analysis and are essential for building quantitative and
qualitative models for secondary analytical techniques, such as NIR e MIR
spectroscopies. However, the performance of conventional wet chemistry
methods is often outperformed by new modern approaches and their
development should be further encouraged, aiming at techniques applicable
at high throughput, with no or little sample preparation, inexpensive, easy to
use, automated and environmentally friendly. So far, this has changed
progressively, because sophisticated studies with online or at-line systems
have been carried out in the recent past. Particularly in the coffee industry,
this is likely to change soon, driven by industries and researchers.
Cup quality characteristics are closely related to the sensory evaluation
of the cuppers. However, from a sensory scientific perspective, cupping is
not equivalent to sensory evaluation. The cupping method faces challenges
related to its subjectivity, reproducibility, and time requirement. Although
there is a subtle similarity between the cupping method and DSA, these
methods are only superficially similar (Giacalone et al. 2019; Di
Donfrancesco, Guzman, and Chambers 2014; Feria-Morales 2002).
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Di Donfrancesco, Guzman, and Chambers (2014) compared the cupping
and DSA results of Colombian coffees. In general, the authors reported that
there is little relationship between cupping and DSA results. Larger
differences in sensory properties between the two procedures were observed
in the differentiation of the same coffee samples. This is not surprising,
considering that the cupping method was designed to assess “quality” and
DSA was designed to assess specific sensory characteristics. This explains
the little relationship between the individual characteristics measured by a
trained sensory panel and the broader quality characteristics measured by
cuppers. Therefore, these results indicate that none of the methods is suitable
for use in all situations.
Individual cuppers use different terms to describe the same coffee,
which provides further evidence the two methods are different and can be
synergistic, with cupping presenting an overall measure of quality and
descriptive sensory analysis, providing a detailed and consistent description
that currently does not exist in cupping. The cupping and DSA panels can
work in synergy. However, further investigation is needed to establish a
relationship and determine whether one of these methods is related to
consumer acceptance, that is, to link to consumer preference (Di
Donfrancesco, Guzman, and Chambers 2014).
A common sensory lexicon is needed by trained panelists to consistently
assess the characteristics of a product and share this information between
different people/panels (Lawless and Civille 2013). Thus, lexicons can be
used for descriptive sensory panels, experts, and consumers to standardize a
sensory vocabulary. Chambers et al. (2016) developed a sensory lexicon for
coffees from 14 countries around the world analyzed by a highly trained
panel assessed using descriptive sensory analysis and PCA. The authors
verified the successful creation of this lexicon. The sensory panel identified
110 attributes (many used for both aroma and flavor) and references and, in
the first phase, the coffee lexicon allowed the panelists to describe specific
characteristics present in coffee samples, such as sweet, nutty and fruity
notes, as well as the differentiation of notes like burnt, smoky, astringent,
acrid and bitter. The attributes and references developed were successfully
used by the trained panel to describe a wide range of coffee samples. The
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lexicon is considered as something “alive”, as additional terms can be added
as needed to expand the lexicon to include attributes that are not yet defined.
The effects of the serving temperature on the descriptive sensory
attributes of coffees have also been investigated by several authors (Chapko
and Seo 2019; Steen et al. 2017; Stokes, O’Sullivan, and Kerry 2016). The
authors observed that the sensory attributes of coffees are affected by the
temperature of the water in which coffee is brewed (Stokes, O’Sullivan, and
Kerry 2016). In addition, influences on the release of volatile compounds
and the intensity of sensory attributes were also observed (Steen et al. 2017).
Likewise, different serving temperatures of the coffee beverage have a
different impact on the aroma. Chapko and Seo (2019) found that most of
the attribute intensities differed significantly with the serving temperature
(70, 55, 40, and 25 °C), and with the coffee variety. Coffee beverages served
at 70 and 55 °C were perceived differently from those served at 40 and
25 °C. The authors concluded that the sensory attributes of brewed coffee
products should be evaluated at multiple serving temperatures due to the
perceptual differences.
Recently, Giacalone et al. (2019) performed dynamic tests to study the
presence of common roasting defects in coffee. The investigated coffees
were manufactured from different roasting processes: standard, dark, light,
scorched, baked, and underdeveloped. The coffee samples obtained from
these beans were evaluated by GC-MS, and SDA by trained assessors, and
a hedonic and sensory evaluation by consumers using a check-all-that-apply
(CATA) questionnaire. Multivariate analyses of aroma, SDA, and CATA
data produced similar sample distributions, showing a clear opposition from
light roasting to dark and scorched roasting, with the normal roasting
showing average values of the main compounds in the aroma. The SDA data
confirmed these indications and showed that the normal roasting has a
balanced sensory profile compared to the other defects. It is important to
note that, normal roasting was also significantly preferred in the consumer
test and significantly associated with the positive attributes of CATA
harmonic, pleasant, and balanced. Overall, these results provide a solid basis
for understanding the chemical and sensory markers associated with
common roasting defects, which coffee professionals can use internally in
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quality control and product development applications. They also
demonstrate that a clean cup (coffee without defects) is associated with
greater consumer preference. From the point of view of sensory science, this
research indicates that the attribute ‘clean cup’ describes a coffee of average
sensory intensity, with high acidity and with many recognizable flavor
attributes. However, the authors used only a single source coffee and further
research that should include more coffee samples is needed.
This chapter presented the state of the art of the methods used to assess
coffee quality using sensory tests and analytical techniques, including
alternative technologies. Although the importance of these methods is
unquestionable, there are still challenges to be overcome about coffee
quality. The need for rapid analysis methods in the food processing
industries facilities becomes important to assess the coffee quality in-line or
on-line ways. In view of the aforementioned information, digital imaging,
and the use of portable devices, including spectrometers and smartphones,
are technologies with great potential to be explored and applied to coffee
analysis in the future. In addition, it is likely that further studies with the
combination of these techniques and conventional spectrometers with
chemometric tools will expand, and more extensive studies will be available
in the future. For practical reasons, the coffee quality criteria, as well as other
foods, should be easily measurable. Thus, portable equipment can be useful
for real-time monitoring, routine analysis, an inspection of processing
control and assessment of coffee quality. Compact, rapid, easy, non-
destructive, and “green” methods are needed for quality control and for
screening in the food industries.
It seems difficult to study coffee in terms of its cup quality with the
exclusive use of conventional or even advanced analytical techniques,
reported in this chapter. Furthermore, although clear effects of production
factors, such as the presence of defects and especially cup quality of the
coffee are known, their exclusive attribution to the cupping method seems
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to be difficult. This does not exclude that these characteristics are employed
as valuable auxiliary criteria in routine analysis and inspection situations.
However, the single cupping method is not equivalent to an adequate
scientific sensory assessment. Despite the reliability and widespread use,
complementary methods for adequate sensory assessment within the
standards of sensory science are encouraged in the future.
M. R. Baqueta thanks Coordenação de Aperfeiçoamento de Pessoal de
Nível Superior (CAPES) for the master scholarship. P. Valderrama thanks
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Coffee aroma is critical for consumer liking and enables price differentiation of coffee. This study applied hyperspectral imaging (1000-2500 nm) to predict volatile compounds in single roasted coffee beans, as measured by Solid Phase Micro Extraction-Gas Chromatography-Mass Spectrometry and Gas Chromatography-Olfactometry. Partial least square (PLS) regression models were built for individual volatile compounds and chemical classes. Selected key aroma compounds were predicted well enough to allow rapid screening (R2 greater than 0.7, Ratio to Performance Deviation (RPD) greater than 1.5), and improved predictions were achieved for classes of compounds - e.g. aldehydes and pyrazines (R2 ∼ 0.8, RPD ∼ 1.9). To demonstrate the approach, beans were successfully segregated by HSI into prototype batches with different levels of pyrazines (smoky) or aldehydes (sweet). This is industrially relevant as it will provide new rapid tools for quality evaluation, opportunities to understand and minimise heterogeneity during production and roasting and ultimately provide the tools to define and achieve new coffee flavour profiles.
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This research presents the use of near-infrared (NIR) spectroscopy as a fast alternative of conventional methods, suitable for in-line use for quality control in the industrial coffee processing. Chemometric models were constructed from spectra of 217 coffees sampled during the period of 5 months of coffee processing, which demonstrates the viability of the NIR spectroscopy in terms of prediction, since it provides realistic variability in chemometric models. In this work, granulometry, moisture content, color, and the infusion time of commercially roasted coffee beans were evaluated by reference methods, NIR spectroscopy, and partial least squares (PLS). Four models were built using 217 roasted coffee samples, differentiated by type of beverage and roast degree. After the model’s optimization by the outlier evaluation, parameters of merit such as residual prediction deviation, sensitivity, analytical sensitivity, the inverse of analytical sensitivity, limits of detection and quantification, adjust, and linearity were calculated. The models showed predictive capacity and high sensitivity in determining the analyzed ones. All these quality control parameters were predicted with adequate correlation coefficient, which ranged from 0.73 to 0.84 and presented satisfactory performance. The parameters of merit presented promising results, indicating that the prediction models developed for granulometry, color, moisture content, and infusion time can be safely used in the coffee industry as an alternative to reference methods. Moreover, the proposed methodology is sample preparation free, fast, simple, efficient, and suitable for in-line uses.
As one of the most consumed beverages in the world, coffee plays many major socioeconomical roles in various regions. Because of the wide coffee varieties available in the marketplaces, and the substantial price gaps between them (e.g., Arabica versus Robusta; speciality versus commodity coffees), coffees are susceptible to intentional or accidental adulteration. Therefore, there is a sustaining interest from the producers and regulatory agents to develop protocols to detect fraudulent practices. In general, strategies to authenticate coffee are based on targeted chemical profile analyses to determine specific markers of adulterants, or nontargeted analyses based on the “fingerprinting” concept. This paper reviews the literature related to chemometric approaches to discriminate coffees based on nuclear magnetic resonance spectroscopy, chromatography, infrared/Raman spectroscopy, and array sensors/indicators. In terms of chemical profiling, the paper focuses on the detection of diterpenes, homostachydrine, phenolic acids, carbohydrates, fatty acids, triacylglycerols, and deoxyribonucleic acid. Finally, the prospects of coffee authentication are discussed.
The aim of this work was to compare two near infrared spectrometers (960–1650 nm) to assess coffee matrices for real-time characterization during processing. A benchtop spectrophotometer built for process measurement, equipped with a rotating acquisition system suitable for in-line analyses (device 1), and a portable spectrophotometer for at-line analyses (device 2) were tested. The experimentation was conducted on green, roasted bean, and ground coffee, relating to three coffee blends, employing samples collected at different steps from the process. A total of 399 (247 green, 76 roasted, and 76 ground coffee samples) and 229 (142 green, 43 roasted and 44 ground coffee samples) samples were analyzed using device 1 and device 2, respectively. Principal component analysis was applied to the spectra of the coffee samples to evaluate the feasibility of real-time characterization for each matrix type, during the different steps of the process. Partial least square regression analysis was applied to develop calibrations to predict moisture content, tap density, and powder granulometry on ground coffee and to estimate moisture on roasted bean with a view of real-time measurements. The Passing and Bablok regression method and Bland–Altman analysis were performed to compare results obtained from the tested devices. Considering the models built on different datasets were based on different blends, quality parameters, and matrices, the results obtained from partial least square models, in cross-validation, gave R² values between 0.21 and 0.98 and between 0.18 and 0.84 for devices 1 and 2, respectively. However, considering the comparison of model results derived from the two devices, no significant differences are noticeable for the most part of the dataset analyzed. Hence, based on the strategy to be undertaken by coffee industry operators, a future real-scale application could be envisaged directly in-line using device 1 or at-line using device 2.
In this work, near infrared (NIR) spectroscopy and multivariate data analysis were investigated as a fast and non-disruptive method to classify green coffee beans on continents and countries bases. FT-NIR spectra of 191 coffee samples, origin from 2 continents and 9 countries, were acquired by two different laboratories. Laboratory-independent Partial Least Square-Discriminant Analysis and interval PLS-DA models were developed by following a hierarchical approach, i.e. considering at first the continent and then the country of origin as discrimination rule. The best continent-based classification model was able to identify correctly more than 98% in prediction, whereas 100% of them were correctly predicted by the best country-based classification model. The inter-laboratory reliability of the proposed method was confirmed by McNemar test, since no significant differences (P > 0.05) were found. Furthermore, a validation was performed predicting the spectral test set of a laboratory using the model developed by the other one.
In most previous studies, brewed coffee samples were served at specific serving temperatures for sensory evaluation. While several recent studies have illustrated that serving temperature does have an impact on sensory attribute intensities of brewed coffee, more elaboration is needed. By focusing on knowledge gaps between earlier studies, this study sought to determine whether and how sensory attributes of brewed coffee can vary as a function of serving temperature and coffee variety. In this study, 6 trained panelists rated intensities of 32 sensory attributes (3 appearances, 12 aromas, 2 tastes, 13 flavors, and 2 mouthfeels) with respect to brewed coffee samples, of each of three varieties (Ethiopian, Kenyan, and Colombian) served at four different serving temperatures: 70, 55, 40, and 25 °C, respectively. The results indicated that intensities of 18 and 7 attributes, respectively, differed significantly with serving temperature and coffee variety. A principal component analysis (PCA) showed the greater amount of data variation could be attributed to serving temperature (63.28%) rather than coffee variety (21.24%), much like the result of a hierarchical clustering analysis. Regression vector (RV) coefficients, determined by a factor score matrix of brewed coffee samples served at different temperatures, revealed that brewed coffee samples served at 70 and 55 °C were perceived differently from those served at 40 and 25 °C. In conclusion, the findings emphasize that sensory attributes of brewed coffee samples should be evaluated at multiple serving temperatures, both higher (70 to 55 °C) and lower (40 to 25 °C) ones, to better capture sensory attributes of brewed coffee than those from a traditional sensory evaluation. Further study is needed to characterize different coffee samples with respect to lessening an overwhelming effect of serving temperature.
The chemical composition of brewed coffee depends on numerous factors: the beans, post-harvest processing and, finally, the extraction method. In recent decades, numerous coffee-based beverages, obtained using different extraction techniques have entered the market. This study characterizes and compares eight extraction coffee methods from a chemical-physical point of view, starting from the same raw material. Specifically, three types of Espresso, Moka, French Press, and 3 filter coffee that for the first time are reported in the scientific literature Cold Brew, V60, and Aeropress are compared. Physical measurements included the quantification of total dissolved solids, density, pH, conductivity, and viscosity. Chemical analyses identified 15 chlorogenic acids (CGAs): six caffeoylquinic acids, one p- Coumaroylquinic acid, one Feruloylquinic Acid, four Caffeoylquinic lactones, and three Dicaffeoylquinic acids. Maximum caffeine and CGA concentrations were found in Espresso coffees, while Moka and filtered coffees were three to six times less concentrated. The classic Espresso method was most efficient for caffeine and CGA recovery, with a yield almost double that of other methods. Per-cup caffeine and CGAs were higher in Cold Brew than Espresso coffees, as a function of the volume of beverage, which ranged from 30 mL (for espresso) to 120 mL (for filtered coffees). In light of these results, it is not possible to establish how many cups of coffee can be consumed per day without exceeding the recommended doses, since according to the applied brewing method, the content of the bioactive substances varies considerably
Coffee sensory properties can depend on several factors such as the species/varieties cultivated, the processing after the harvesting phase, geographical origin, and climatic factors. The impact of microclimates has been suggested to be critical to coffee sensory properties. Thirteen Arabica coffee samples from different farms in different sub areas of the same municipality (Pitalito region of Huila, Colombia), were evaluated using descriptive sensory analysis. The coffee samples differed in growing altitude, shading level, and fermentation practices. Overall, samples differed for attributes such as burnt, acrid, ashy, metallic, sour and sweet aromatics. However, differences generally were small, <1-point on a 0‐15 scale for most attributes. Differences could not be directly attributed to geographical area, different farming practice, or storage methods. This study suggests that the impact of specific microclimates within the same small region does not have a large impact on sensory properties of coffee.
The aim of this review is to describe the volatile aroma compounds of green coffee beans and evaluate sources of variation in the formation and development of coffee aroma through postharvest processing. The findings of this survey showed that the volatile constituents of green coffee beans (e.g., alcohols, aldehydes, and alkanes) have no significant influence on the final coffee aroma composition, as only a few such compounds remain in the beans after roasting. On the other hand, microbial-derived, odor-active compounds produced during removal of the fruit mucilage layer, including esters, higher alcohols, aldehydes, and ketones, can be detected in the final coffee product. Many postharvest processing including drying and storage processes could influence the levels of coffee aroma compositions, which remain to be elucidated. Better understanding of the effect of these processes on coffee aroma composition would assist coffee producers in the optimal selection of postharvest parameters that favor the consistent production of flavorful coffee beans.
O presente estudo foi desenvolvido para investigar o potencial dos ácidos orgânicos e bioativos presentes no grão cru para discriminar a qualidade sensorial do café proveniente de diferentes genótipos e métodos de processamento. Durante as safras 2010, 2011 e 2012, foram analisadas a qualidade da bebida do café e o perfil de ácidos orgânicos e dos bioativos, cafeína, trigonelina e ácidos clorogênicos (3,4 e 5-CQA) do grão cru de amostras representativas dos genótipos Bourbon Amarelo e Acaiá. As amostras foram coletadas em lavouras comerciais com altitudes variando entre 932 a 1391 m, no município de Carmo de Minas, MG, Brasil. Os métodos de processamento adotados foram: via seca (café natural) e via úmida com descascamento e desmucilamento mecânico do fruto. Todos os procedimentos de colheita e pós-colheita foram realizados conforme as principais tecnologias para produção de cafés especiais. A análise sensorial foi realizada utilizando-se a metodologia proposta pela Associação Americana de Cafés Especiais (SCAA). As análises químicas foram realizadas por HPLC. Os dados foram investigados aplicando-se a Análise de Componentes Principais (ACP). As variações nos teores de ácidos orgânicos e dos bioativos analisados ocorreram em razão do método de processamento do café. Para os genótipos Bourbon Amarelo e Acaiá, as diferenças existentes no perfil de ácidos orgânicos associado com os bioativos, cafeína, trigonelina e ácidos clorogênicos (3,4 e 5-CQA) foram determinantes para discriminar a qualidade do café descascado e desmucilado mecanicamente.