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European Food Research and Technology 
https://doi.org/10.1007/s00217-022-04118-4
ORIGINAL PAPER
Relationship between physical changes in the coffee bean due 
to roasting profiles and the sensory attributes of the coffee beverage
Larissa Marcia Anastácio1  · Marliane de Cássia  Soares da Silva1  · Danieli Grancieri Debona2  · 
Tomas Gomes Reis Veloso1  · Thaynara Lorenzoni Entringer1  · Vilian Borchardt Bullergahn1  · 
José Maria Rodrigues da Luz1  · Aldemar Polonini Moreli2  · Maria Catarina Megumi1  · Lucas Louzada Pereira2 
Received: 8 June 2022 / Revised: 1 September 2022 / Accepted: 2 September 2022 
© The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2022
Abstract
The physical or morphological integrity of the coffee bean during post-harvest processing directly influences the economic 
value and sensory quality of the coffee beverage. Breakdowns in the outer layers of the beans are characteristics observed 
for the morphological and economic classification of coffee beans during the commercialization of this product. However, 
physical changes in the inner layers of the beans that are not seen with the naked eye can also influence the sensory quality of 
the coffee. Therefore, the objective of this study was to relate changes in the physical structure of coffee beans roasted by four 
different processes (light, medium, dark, and baked) with the sensory attributes of the beverage. The analyses of the physical 
characteristics of the coffee beans were carried out by X-ray microtomography and the sensory profile was determined using 
the Specialty Coffee Association of America protocol. The roasting profile with the highest sensory scores showed higher 
values for total pore space volume and a negative Euler number. However, the roasting profiles that fluctuated between the 
highest and lowest of scores of the sensory attributes did not present standardized behavior for the connectivity, Euler number, 
and total pore space volume. Hence, morphological or physical changes in the coffee beans caused by the different types of 
roasting correlate with changes in the sensorial profile. Furthermore, the sensory discrimination of these coffee beans among 
the different roast profiles may be observed by the joint analysis of the flavor and fragrance scores.
Keywords Connectivity · Porosity · Euler number · Sensory analysis · Coffee quality
 * Lucas Louzada Pereira 
 lucaslozada@hotmail.com
 Larissa Marcia Anastácio 
 larissa.anastacio@ufv.br
 Marliane de Cássia Soares da Silva 
 mcassiabio@yahoo.com.br
 Danieli Grancieri Debona 
 danielidebona@hotmail.com
 Tomas Gomes Reis Veloso 
 tomasgomesrv@gmail.com
 Thaynara Lorenzoni Entringer 
 thaynara.entringer@ufv.br
 Vilian Borchardt Bullergahn 
 vilianborchardt@gmail.com
 José Maria Rodrigues da Luz 
 josemarodrigues@yahoo.com.br
 Aldemar Polonini Moreli 
 aldemar.moreli@ifes.edu.br
 Maria Catarina Megumi 
 catarinakasuya@gmail.com
1 Departamento de Microbiologia, Laboratório de 
Associações Micorrizicas, LAMIC, Universidade 
Federal de Viçosa (UFV), Avenida Ph Rolfs S/N, Viçosa, 
Minas Gerais-Mg 36570-000, Brazil
2 Coffee Design Group, Venda Nova Do Imigrante, Federal 
Institute of Espírito Santo (IFES), Rua Elizabeth Minete 
Perim, S/N, Bairro São Rafael, Espírito Santo-ES 29375-000, 
Brazil
http://orcid.org/0000-0001-8283-3177
http://orcid.org/0000-0003-4678-7876
http://orcid.org/0000-0003-2091-9826
http://orcid.org/0000-0001-6874-8208
http://orcid.org/0000-0002-2468-2750
http://orcid.org/0000-0002-8235-0594
http://orcid.org/0000-0001-9826-7982
http://orcid.org/0000-0002-6659-5807
http://orcid.org/0000-0002-9539-9370
http://orcid.org/0000-0002-4436-8953
http://crossmark.crossref.org/dialog/?doi=10.1007/s00217-022-04118-4&domain=pdf
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Introduction
Coffee is a commodity of high economic importance 
and produces one of the most consumed beverages in the 
world, totaling more than two billion cups a day [1].
The sensory quality of the beverage depends on the raw 
material (coffee bean), including species, plant variety, 
and post-harvest processing [2, 3]. Changes in the physical 
structure (bean microstructure and color), in the chemical 
composition and in the sensory attributes due to roasting 
influence the final coffee quality [4].
The chemical composition of coffee beans includes 
alkaloids, phenolic compounds, carbohydrates, amino 
acids, proteins, and lipids [5]. It is also possible to find 
bioactive compounds, such as caffeine, organic acids, 
alcohols, and non-digestible fibers [6]. However, roasting 
changes the chemical composition of coffee [7, 8].
During roasting, physical and chemical changes occur 
and the ideal point of the roasting is determined using the 
sound, color, volume and texture of the coffee bean, and 
sensory attributes of beverage [9].
The high roasting temperatures produce melanoidins 
and gases, such as water vapor and carbon dioxide [6, 
10]. The brown color of beans during roasting is due to 
melanoidins and gases generating vapor pressure inside 
the cells of the coffee beans. Internal pressure causes the 
expansion of volume, increase of porosity, and decrease 
of density of the coffee bean at the end of roasting [10]. 
Furthermore, the morphological integrity of the coffee 
bean during post-harvest processing, such as drying, husk 
removal and roasting, directly influences the economic 
value and sensory quality of the coffee beverage [7, 8, 
11, 12]. Breakdowns in the outer layers of the beans are 
characteristics observed for the morphological and eco-
nomic classification of coffee beans during the commer-
cialization of this product [13]. However, physical changes 
in the inner layers of the beans that cannot be seen with 
the naked eye can also influence the sensory quality of 
coffee. According to Giacalone et al. [8], the chemical 
and sensory markers of coffee quality are associated with 
roasting defects (e.g., dark, light, scorched, baked, and 
underdeveloped).
X-ray microtomography (MicroCT) allows for the visu-
alization of small materials with high resolution and may 
help in the evaluation of physical alteration caused by cof-
fee bean roasting. This technique has been used in the 
analyses of soil, microbes, animal tissues, and food [11, 
14–17]. MicroCT has also been used to analyze changes in 
the microstructure of coffee beans before and after roast-
ing [18, 19]. Bustos-Vanegas et al. [20] showed the evo-
lution of the internal matrix of coffee beans during the 
roasting process with temperature variation between 200 
and 280 °C using MicroCT. However, there are no reports 
of this technology applied to evaluate the integral roast-
ing process in short time intervals, which would provide 
an understanding of the coffee bean structure during the 
roasting curve.
According to Pires et al. [21], MicroCT does not cause 
much damage to the materials and may be used to evaluate 
porosity, connectivity, tortuosity, and the Euler number of 
undisturbed samples. Furthermore, this technique allows 
the reconstruction of three-dimensional images through its 
two-dimensional transversal projections [22].
The effect of roasting on sensory attributes is performed 
by the cup test [23]. These sensory analyses can also be 
influenced by relative humidity, ambient temperature, bean 
quality, ideal roasting point, brewing, and the perception 
of panelists [7, 24].
Thus, the objective of this study was to evaluate the 
changes in physical structure using X-ray microtomogra-
phy and in the sensory profile of coffee beans roasted by 
four different roasting process (light, medium, dark, and 
baked). Evaluating physical and chemical changes dur-
ing roasting is essential to developing strategies to assess 
the quality of coffee beans, with different sensory pro-
files and characteristics. Additionally, the use of MicroCT 
allows for observation of the physical changes in the inter-nal structure of the coffee bean, which occur in different 
types of roasting and affect the final quality of the coffee 
beverage.
Similar to our study, Bustos-Vanegas et al. [20] describes 
the physical variations in the coffee bean by MicroCT during 
the roasting process. The techniques used in the two articles 
to assess coffee quality are similar, but the objectives are 
different. We related these changes to the coffee sensory 
profile, while Bustos-Vanegas et al. [20] intended to deter-
mine mathematical expressions to be used in heat and mass 
transfer models in the roasting process.
Materials and methods
Selection and preparation of green coffee beans
The coffee fruits (Coffea arabica L., of the Catucaí Ver-
melho-785 variety) were manually collected with 90% matu-
ration in a farm in the montane region of the state of Espírito 
Santo, Brazil. These ripened fruits were processed by the 
semi-dry method [2] and placed on a suspended terrace to 
dry until they reached 12% of wet mass. After drying, the 
coffee beans were submitted to the physical classification 
process and only beans free of defects on the 16 # UP sieve 
equivalent to 16/64 of one inch were used for the roasting 
procedures [25, 26].
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Density calculation
The density of coffee beans was determined by mass (kg) 
of the dry beans contained in a one-liter container.
Roasting process
Four roasting profiles—baked, light, medium, and dark—
were applied in coffee beans using a Type 2 Probatino 
roaster (Probat Leogap, Curitiba, Paraná, Brazil) coupled 
with Cropster software. These profiles were based on the 
studies of Chu et al. [27] and De Luca et al. [28]. The 
initial temperature was 150 °C (Fig. 1). During roast-
ing, there was variation in the temperature per minute 
according to the roasting profile. The final roasting time 
was determined for each roasting profile by comparing 
the bean color with the Agtron Discs scale from Agtron 
Inc. The roast reference numbers #80, #68, #65, and #56 
were adopted for light, baked, medium, and dark roasts, 
respectively (Fig. 1).
At each minute of the roasting process, a sample (10 g) 
was taken from the roaster (Fig. 1). The samples were 
stored in high-density polyethylene bags, with the follow-
ing number of samples collected for each roasting pro-
cess: 20 samples for the baked, 9 for light, 10 for medium, 
and 12 for dark roasting.
At the end of roasting, the roasted coffee beans were 
stored in metalized polyester packages, with an aromatic 
valve to exhaust the gases. These samples (100 g of each 
roast profile) were used in the sensorial analysis.
Microtomographic analysis
The X-ray microtomography analyses were performed in the 
Microscopy and Microanalysis Nucleus of the Universidade 
Federal de Viçosa using 51 samples of coffee beans roasted 
with different roasting times.
The coffee beans were fixed and positioned in the appro-
priate sample holder of the equipment (SkyScan1174v2 
Scanner). For the complete stabilization of the material, a 
cylindrical styrofoam cube was used to secure the vertical 
position of the object throughout the scanning stage.
The settings used followed pre-set standards established 
by the manufacturer, with a working voltage of 50 kV and 
current of 800 mA. After scanning the material, three types 
of processes occurred: image reconstruction, quantifica-
tion of variable parameters, and three-dimensional analy-
sis. The image reconstructions were made by the NRECON 
(v 1.7.3.0) software with the average of 480 slices. For 
three-dimensional visualization, CTAn software (version 
1.16) was used for the following parameters: percentage 
of volume per working area, porosity, and connectivity, as 
recommended by Bouxsein et al. [29]. The projections of 
the reconstructed slice sections from the Nrecon program 
enabled the generation of 3D images, which were analyzed 
under the region and volume of interest selected.
Processing of the images
The three-dimensional image generation was obtained 
from the reconstruction in the Nrecon program, which pro-
cesses the images from the cross-sections and generates a 
three-dimensional model. After the image reconstruction, 
Fig. 1 Roasting profiles of cof-
fee beans submitted to baked, 
light, medium, and dark roasting 
in a Probatino roaster (Type 2)
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the analyses were done using the CTAn software. The pro-
gram consists of the image binarization process, where the 
values established for the binarization of the object are 
given through the histogram along with the visual analysis, 
which can be observed in grayscale [30]. The tools used in 
MicroCT were able to continuously capture three-dimen-
sional images. Furthermore, the first mathematical calcula-
tion of images was performed by selection of the region of 
interest (ROI) of the sample [31].
The volumetric calculations of the object aggregating all 
slices into a single structure was done by the interpolation 
of the ROI's. This interpolation was performed according 
to the geometric shape chosen that best fits the coffee bean. 
The determination of the volume of interest (VOI) was also 
done by interpolating the ROI. The VOI produces physical 
data about the interior of the coffee bean. These steps are 
important for 3D analysis [31].
Analysis of three‑dimensional (3D) volumetric 
measurements
The three-dimensional quantitative analysis of the volume 
 (mm3), surface area (mm2), porosity, density, connectiv-
ity, and Euler number was performed using the 3D analysis 
plug-in. The other physical variables (e.g., structure model 
index, structure thickness, structure linear density, structure 
separation, fractal dimension, number of objects, number 
of closed pores, volume of closed pores, surface of closed 
pores, closed porosity, volume of open pore space, open 
porosity, total volume of pore space, total porosity, and con-
nectivity density) were also made in these 3D analyses. In 
three-dimensional models, the differences in the intensity 
of coloration are perceived according to the density of each 
part of the bean region.
Parameters of evaluation obtained 
through three‑dimensional visualization
The volume, apparent density, number of pores, porosity, 
and connectivity were used for the characterization of the 
samples in the CTAn software [32]. The sample volume was 
obtained by multiplying the number of pixels by the volume 
of the voxel. Apparent density was calculated by dividing 
the sample mass by the sample volume. Pixel density was 
obtained by calculating the attenuation coefficient of the 
material.
The number of pores measures the number of connections 
of the structure before being separated into two parts [11]. 
The porosity is the volume of pores detected in the structure 
and can distinguish between open and closed pores. The con-
nectivity measures the degree of multiplication of geometric 
structure [11].
Sensorial analysis
The sensorial analysis was performed according to the 
guidelines of the Specialty Coffee Association [26]. The 
roasted coffee beans were ground at medium granulometry, 
with 70 and 75% of the particles passing through a 20-mesh 
sieve (US Standards). Five cups were made using 8.25 g of 
coffee powder of each roasting profile [2, 7, 33]. These cups 
were randomly placed on the tasting table and the infusion 
of ground coffee was performed with 150 mL mineral water 
at 94 °C for 4 min. Twelve minutes after the infusion, six 
Q-graders (panelists) evaluated 11 sensory attributes of the 
coffee beverage: fragrance/aroma, uniformity, clean cup, 
sweetness, flavor, acidity, body, aftertaste, balance, overall 
assessment, and overall score [7, 23, 26]. The panelists gave 
scores ranging from 0 to 10 points for each sensory attribute.
Statistical analysis
A Principal Component Analysis (PCA) based on Euclidean 
distance was performed to evaluate the changes in the inter-
nal structure of coffeebeans during the roasting process. 
The physical variables obtained by MicroCT were used in 
the PCA. The analysis was performed using the package 
Factoextra in R 3.6.3. The percentage change between each 
pair of adjacent times was calculated based on the Euclidean 
distance between the ordination vectors.
The statistical differences among the grades of each sen-
sory attribute of the beverage were evaluated by one-way 
ANOVA followed by Tukey’s test at 0.05 probability.
Results and discussion
During the roasting process, the coffee bean coloring 
changed from green to yellow, yellow to shades of brown, 
and finally to a dark brown color (Fig. 2). These changes 
in color may be due to the degradation and/or formation 
of chemical compounds caused by temperature (Figs. 1, 2). 
The chemical composition of roasted coffee beans depends 
on the roasting profile and are responsible for the aroma and 
flavor of the coffee beverage [34].
The dark brown color was due to an increased degree 
of roasting (Fig. 2). Melanoidins are brown nitrogenous 
chromophores formed from Maillard reactions [35]. These 
compounds are the principal factors responsible for the color 
changes in the coffee beans during roasting [36].
A loss of density of coffee beans was observed after roast-
ing (Table 1). These reductions were directly proportional to 
the exposure time of the samples in the roaster and occurred 
due to water evaporation and release of gases from the ther-
mal reactions of solid compounds [37]. These gases are the 
driving forces for uniform expansion of the coffee beans 
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[38]. According to Bustos-Vanegas et al. [20], bean den-
sity varies linearly with the moisture level and decreases 
at roasting temperatures above 220 °C. Furthermore, this 
expansion may cause visible fractures in beans and rupture 
of the cells [12].
In the light roast profile changes in color from green to 
shades of brown were observed (Fig. 2) with the small-
est expansion of beans and highest density (Table 1). On 
the other hand, the dark and baked profiles showed more 
expanded beans, lower density, more dark color than the 
medium profile (Fig. 2, Table 1). The changes of color, and 
density of coffee beans in the dark and baked profiles may 
be due to the release of oils on the surface of beans and 
carbonization of the cellulosic structures. This release of 
oils has been observed in coffees of the Agtron roast grade, 
which is equivalent to dark roasts [39].
Changes in physical structure not visible to the naked 
eye also occur in coffee beans along the roasting process, 
providing data on how they behave when subjected to differ-
ent time and temperature gradients (Fig. 3, Supplementary 
Fig. 1). Over time of roasting, the beans expand due to the 
induction of water vapor and carbon dioxide (Fig. 3). Empty 
spaces in beans are formed within the parenchymatic and 
mucilaginous tissues during roasting [40]. The pores and 
empty cells are formed by thermal degradation of organic 
components of the plant cell [19]. These empty spaces are 
produced in greater quantity in immature or underdeveloped 
bean than in defect-free coffee beans [41]. However, beans 
with the lowest degree of roasting have better interconnected 
and compact cell walls, creating a continuous density, aris-
ing from layers filled with cells with lipids and proteins [19]. 
That is why the initial beans had a grayish color (Fig. 3a, 
d, g, j).
The dimensions and shapes of pores formed in coffee 
beans were influenced by roasting profiles (Fig. 3b, c, e, f, h, 
i). Coffee beans have large and elongated pores in the outer 
areas and rounded and uniform in the inner areas which can 
form cavities in roasted beans [19]. This phenomenon may 
be observed by comparing the beans before (Fig. 3a, d, g, j) 
and after roasting (Fig. 3b, c, e, f, h, i) and are represented 
by black spaces inside the beans (Supplementary Fig. 1). 
According to Pittia et al. [19], the cavities in the roasted 
beans may be due to non-complete degradation of polysac-
charides of the external walls and asymmetric fusion of two 
or more pores. Furthermore, the final bean volume of the 
coffee beans after roasting was about two times greater than 
the initial volume [20].
The MicroCT analysis also allowed for evaluation and 
identification of changes in several parameters for all types 
of roasting applied. These parameters are expressed in the 
percentage of physical variations, which occurred in time 
intervals (Fig. 4). Isotropic volumetric expansion in roasting 
temperatures above 220 °C was observed in coffee beans 
evaluated every 20 s of roasting times [20].
The variation in the data analyzed for the light (42.7%) 
and medium (42.2%) roasts were higher in the last three 
roasting intervals than at other times (Fig. 4). Therefore, 
more than 40% of the variation of the data occurred in only 
30% of the routine time of the roasting process (Fig. 4). 
Meanwhile, the highest variation (63.7%) for the dark roast 
was observed after 7 min of roasting. According to Pereira 
and Moreira [42], the greatest variation of the Euclidean 
distance in the bean of these three roasts is observed after 
7 min. The thermal reactions which alter the physical and 
chemical structure of the bean occur in this time [42]. It is 
important to emphasize that for the dark roast, these varia-
tions maintain this behavior pattern after the tenth minute, 
Fig. 2 Digital photographs of 
coffee beans during the light, 
medium, dark, and baked roast-
ing profiles. These profiles were 
obtained in a Probatino roaster 
(Type 2)
Table 1 Physical data of coffee beans submitted to baked, light, 
medium, and dark roasting in a Probatino roaster (Type 2)
Roasting profile Roasting time 
(min:s)
Density (kg/L)
Initial Final Variation
Light 08:40 1.2 1.116 − 0.084
Medium 09:50 1.2 1.080 − 0.120
Dark 11:15 1.2 1.052 − 0.148
Baked 20:00 1.2 1.048 − 0.152
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because this is the moment when the reactions exceed the 
time necessary to generate positive sensory characteristics. 
This leads to carbonization, which affects the structure of 
the beans and their sensory qualities [43].
The variations in baked roast were mostly halfway 
through the roasting time and after 13 min a stabilization 
in these variations was observed (Fig. 4). This phenome-
non can be attributed to the endothermic process exerted 
on beans. The increases of gradual temperature and roast-
ing time causes the temperature variation per minute to be 
higher in the initial minutes (Fig. 1) and thermal reactions, 
such as Maillard's, occur in the subsequent minutes when the 
temperatures are higher than 170 °C (Fig. 1). According to 
Pimentel et al. [44], the characteristic reactions of roasting 
such as Maillard and caramelization of carbohydrates are 
observed in temperatures above 170 °C. Furthermore, these 
thermal reactions change the chemical and physical structure 
of the coffee beans [10].
The variation observed in coffee beans shows the impor-
tance of the precision of the roasting time to obtain tech-
nical parameters of process control and sensory quality of 
the beverage (Fig. 4). To reach the desired result of bever-
age quality, the roasting process can be exemplified as a 
series of successive reactions, which are activated by highly 
controlled heating that will contribute to the formation of 
characteristic coffee flavor and aroma [43]. Among other 
aspects, performing the highly accurate control of time 
and temperature is crucial since this binomially affects the 
organoleptic properties of coffee, as well as the intensity and 
relative composition of the components of the bean, which 
is essential for the control of the quality parameters of this 
beverage [34].
Fig. 3 Microtomographic 
images of coffee beans during 
the roasting profiles light (a–c), 
medium (d–f), dark (g–i), and 
baked (j–l). Coffee beans were 
removed at the start(a, d, g, and 
j), middle (b, e, h, and k), and 
end (c, f, i, and l) of the roasting 
process. The time of each of 
these sample removal phases 
may differ due to the roasting 
profile (Fig. 1)
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The variation peaks isolated along the roasting time inter-
vals were also observed for light roasting in time intervals 
2–3 (14.8%), 4–5 (17.1%), and 7–8 (26.8%) minutes and for 
medium roasting in intervals of 1–2 (17.4%), 6–7 (11.2%), 
and 8–9 (20.6%) min (Fig. 4). These sets of variations can 
relate to the stages of roasting: dehydration, the onset of 
the main reactions, and cracking. Dehydration occurs in the 
first minutes (1st to 3rd) of roasting and is characterized by 
the release of water molecules that culminate in a loss of 
mass and a slight expansion of the beans [12]. In the fol-
lowing minutes (5th to 6th), other changes occur in the cof-
fee beans due to pyrolytic and Maillard reactions causing 
oxidation, reduction, hydrolysis, and polymerization of solid 
compounds. These thermal processes produce volatile and 
non-volatile compounds responsible for the color, aroma, 
flavor, and sweetness of the coffee [45]. We also observe 
that the coffee beans acquire a brownish color after 5 min 
of roasting (Fig. 2).
The highest variation peaks were observed in the final 
minutes of the roasting profiles, after 8 min when the first 
crack begins (Figs. 3, 4). This crack in the coffee beans 
(Fig. 3) may be due to the thermal degradation of saccharose 
with release of gases that cause an increase in the internal 
pressure of the grains and rupture their physical structure 
[12].
In the dark roast profile, three other peaks in the intervals 
of 9–10, 10–11, and 11–11.16 min were observed (Fig. 4). 
These peaks relate to the second crack due to prolonged 
Fig. 4 Percentage of variation observed in the coffee beans during the light, medium, dark, and baked roasting profiles. These percentages are 
based on the Euclidean distance among the vectors of the first four dimensions of the principal component analysis
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roasting and increased release of carbon dioxide through the 
thermal degradation of organic compounds. At this stage, the 
bean becomes extremely dark (Fig. 2), and the flavors and 
aroma are enhanced by bitterness [46] due to the formation 
of pyrazines and pyridines [47].
Since it is characterized by a prolonged roasting which 
takes longer to reach high temperatures (Fig. 1), the baked 
profile has its variation peaks at different times compared to 
the other profiles. The peaks in the intervals of 3–4 (9.4%), 
8–9 (7.4%), 10–11 (12%), 11–12 (16.1%), and 12–13 (9.1%) 
min are noteworthy. However, these peaks create a gap to 
be studied to understand and relate physical changes with 
chemical reactions that occur during roasting of coffee 
beans.
For all roasting profiles, the variables related to poros-
ity and connectivity were the ones that most contributed to 
the sorting of the samples (Fig. 5). These variables tended 
to increase throughout the roasting process. However, the 
Euler number showed inversely proportional behavior to the 
roasting time (Fig. 5). Connectivity is a property based on 
the geometry of the pore-bond networks and is related to the 
amount of bean porosity [48]. The pores describe the overall 
open structure of desiccated material, where it comprises 
the fraction of the void volume [49]. The Euler number is a 
dimensionless indicator that shows how a pore is connected 
to other pores [11]. Therefore, the lower the Euler number, 
the better the connectivity among pores [50].
Given this, the relationship between porosity and con-
nectivity during the roasting process was strictly linked to 
the characteristic of coffee friability (Fig. 5). As the bean 
becomes more roasted, lower Euler numbers and higher lev-
els of porosity and connectivity are observed [11, 51]. This 
set of physical changes increases bean friability, making it 
increasingly expansive, easier to be broken or crushed, and 
with a shorter shelf life [51]. Because of this, when looking 
at the light and medium roast profile variables, a similar 
final value is identified for Euler’s number and total vol-
ume pore space, with a greater difference for connectivity 
(Fig. 6). Specifically, the medium roast had higher connec-
tivity numbers than the light roast. The dark roast, on the 
other hand, had an Euler number of -606 (in 10 min of roast-
ing) and showed the highest connectivity among all roasts 
(2591). The inverse occurs for the baked roast with an Euler 
number and connectivity of 1079 and 915, respectively, at 
the end of the process. Therefore, the study of these physi-
cal variables (e.g., connectivity, Euler number, porosity, and 
friability) may help to understand the effects of roasting on 
the physical and chemical changes of the coffee bean and 
the relationship of these changes with the sensory quality 
of the coffee beverage.
In the sensory analysis (Fig. 7), we observed that the 
grades assigned to the light and medium roasting profiles 
had similar final grades. Pereira et al. [12] observed that 
the variation of the temperature gradient over time was not 
significant to differentiate these roasting profiles in the sen-
sory analyses. However, the scores for fragrance and acidity 
were better in medium roasting than other roasting (Fig. 7).
For the attributes of balance, body, aftertaste, and flavor, 
the light roast stood out (Fig. 7). The dark roast had inter-
mediate grades between the light/medium and the baked 
roast profiles, which had the worst final grade (Fig. 7). The 
baked roast received the lowest final score and this trend 
was repeated for all other attributes, for example, its after-
taste had the lowest evaluation among all sensory attributes 
analyzed. These results may be due to the prolonged time 
of roasting and mild temperatures, which cause physical 
(Figs. 2, 3, 4 and 6) and chemical changes in the coffee 
beans. The lack of adjustment of time and temperature con-
ditions in the coffee bean roasting process can contribute 
to the production of compounds that negatively affect the 
sensory characteristics of the coffee beverage [52].
Conclusions
The morphological or physical parameters of coffee beans 
change (Figs. 2, 3, 4, 5, 6, Table 1) due to the different types 
of roasting (Fig. 1), which correlate with changes in the sen-
sory profile (Fig. 7). Parameters such as connectivity and 
Euler’s number are inversely related to each other (Figs. 4 
and 6). On the other hand, for the results shown, the highest 
Euler number is related to the roasting profile that received 
the lowest sensory evaluation (Fig. 7) and presented the low-
est connectivity value (Fig. 4). The roasting profile with the 
highest sensory evaluation also showed higher values for 
total pore space volume and a negative Euler number (Figs. 4 
and 6). The roasting profiles that fluctuated among the high-
est and lowest sensory scores did not present standardized 
behavior for the connectivity, Euler number, and total pore 
space volume parameters (Figs. 4, 5, 6, 7). Meanwhile, the 
sensory discrimination among the roast profiles may be 
observed by the joint analysis of the flavor and fragrance 
scores (Figs. 1 and 7). Furthermore, MicroCT also allows a 
correlation of physical changes in the internal structure of 
coffee beans with the sensory profile of the coffee beverage.
European Food Research and Technology 
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Fig. 5 Principal component 
analysis of coffee beans with 
different roasting profiles (light, 
medium, dark, or baked) based 
on X-ray microtomography. The 
scatter plots (on the left) show 
the ordering of the samples with 
time of roasting, while those 
on the right show the contribu-
tion of each physical variable to 
these orderings
 European Food Research and Technology
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Fig. 6 Euler number, porosity, and connectivity of coffee beans duringthe light, medium, dark, and baked roasting profiles. On the coordinate 
axes, the roasting temperature range is displayed on the right and the porosity or connectivity values on the left
Fig. 7 Sensory attributes of 
coffee beans submitted to 
baked, light, medium, and dark 
roasting. Values followed by the 
same letter did not differ by the 
Tukey test
European Food Research and Technology 
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Supplementary Information The online version contains supplemen-
tary material available at https:// doi. org/ 10. 1007/ s00217- 022- 04118-4.
Acknowledgements The authors would like to thank Sul Serrana 
of Espírito Santo Free Admission Credit Cooperative—Sicoob 
(23186000886201801), FAPEMIG (Fundação de Amparo à Pesquisa 
de Minas Gerais), CAPES (Coordenação de Aperfeiçoamento de Pes-
soal de Nível Superior—Código de Financiamento 001), CNPq (Con-
selho Nacional de Desenvolvimento Científico e Tecnologia), and Insti-
tuto Federal do Espírito Santo, for supporting the research, through the 
PRPPG n°. 10/2019—Productivity Researcher Program—PPP and the 
Q-Graders for their cooperation in this study. We are also very thankful 
to Núcleo de Microscopia e Microanálises (NMM) of the Universidade 
Federal de Viçosa, where the X-ray microtomography analyses were 
performed and Cropster Brasil for donating the license for Cropster 
software.
Funding The Sul Serrana of Espírito Santo Free Admission Credit 
Cooperative—Sicoob (23186000886201801), CAPES (Coordenação 
de Aperfeiçoamento de Pessoal de Nível Superior—Código de Finan-
ciamento 001), CNPq (Conselho Nacional de Desenvolvimento Cientí-
fico e Tecnologia—Código 304087/2020–3), and Instituto Federal do 
Espírito Santo, for supporting the research through the PRPPG no. 
10/2019—Productivity Researcher Program—PPP.
Declarations 
Conflict of interest The authors declare that they have no conflict of 
interest.
Compliance with ethics requirements All procedures performed in 
studies involving human participants were in accordance with the ethi-
cal standards of Sensory Dimensions, United Kingdom.
Informed consent All participants of the QDA and Napping panels 
were provided with consent forms before taking part in this study at 
Sensory Dimensions.
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	Relationship between physical changes in the coffee bean due to roasting profiles and the sensory attributes of the coffee beverage
	Abstract
	Introduction
	Materials and methods
	Selection and preparation of green coffee beans
	Density calculation
	Roasting process
	Microtomographic analysis
	Processing of the images
	Analysis of three-dimensional (3D) volumetric measurements
	Parameters of evaluation obtained through three-dimensional visualization
	Sensorial analysis
	Statistical analysis
	Results and discussion
	Conclusions
	Acknowledgements 
	References