© The Authors, 2024, Published by the Universidad del Zulia*Corresponding author:
smurillob@undac.edu.pe
Keywords:
Specialty coees
Greenhouse
Tasting
Sensory
Safety
Physical and sensory quality of coee dried in three prototypes of greenhouse solar dryers
Calidad física y sensorial del café secado en tres prototipos de secadores solares tipo invernadero
Qualidade física e sensorial do café seco em três protótipos de secadores solares de estufa
María de Jesús Huamán-Murillo
1
Shirley Mayhory Mejía Garcia
2
Silvia María Murillo-Baca
2*
Fortunato Candelario Ponce-Rosas
2
Maria Jose Fuentes-Meza
2
Rev. Fac. Agron. (LUZ). 2024, 41(2): e244112
ISSN 2477-9407
DOI: https://doi.org/10.47280/RevFacAgron(LUZ).v41.n2.02
Crop production
Associate editor: Dr. Jorge Vilchez-Perozo
University of Zulia, Faculty of Agronomy
Bolivarian Republic of Venezuela
1
Universidad Nacional del Centro del Perú, Facultad de
ingeniería en Industrias Alimentarias, Huancayo, Junín,
Perú.
2
Universidad Nacional Daniel Alcides Carrión, Facultad de
Ciencias Agropecuarias, Escuela de Formación Profesional
de Industrias Alimentarias. Calle Daniel Alomia Robles s/n,
Chanchamayo, Junín, Perú.
Received: 05-03-2024
Accepted: 25-03-2024
Published: 09-04-2024
Abstract
Reducing the drying time of coee without causing negative eects on
cup quality has been the subject of several investigations. The objective was
to determine the eect of three variants of a greenhouse-type solar dryer
prototype on the physical, sensory and microbiological quality of coee. The
solar dryer prototype with three variants, prototype 1 (P1) greenhouse solar
dryer, prototype 2 (P2) solar dryer with air extractor and prototype 3 (P3)
solar dryer with air extractor and solar powered heaters, was compared to
traditional drying (T0) (cement oor). Drying time, physical grain defects,
yield, sensory and microbiological quality were evaluated. The best results
were obtained in P3 with a drying time of 52 h (2 ¼ days), with dry parchment
coee beans without primary defects, higher yield in exportable gold coee
(83.24 %), sensory prole of 84.25 points qualied as specialty coee (with
Q Premium grade) and better safety than coee obtained by traditional
drying; demonstrating that the greenhouse type solar dryer with air extractor
and solar energy heaters is a sustainable alternative to improve the eciency
of coee drying while preserving its sensory quality, an essential value for
producers to achieve better prices.
This scientic publication in digital format is a continuation of the Printed Review: Legal Deposit pp 196802ZU42, ISSN 0378-7818.
Rev. Fac. Agron. (LUZ). 2024, 41(2): e244112 April-June. ISSN 2477-9407.2-6 |
Resumen
Reducir el tiempo de secado del café sin ocasionar efectos negativos
en la calidad en taza ha sido motivo de diversas investigaciones. El
objetivo fue determinar el efecto de tres variantes de un prototipo
de secador solar tipo invernadero en la calidad física, sensorial
y microbiológica del café. El prototipo de secador solar con tres
variantes, prototipo 1 (P1) secador solar tipo invernadero, prototipo
2 (P2) secador solar con extractor de aire y prototipo 3 (P3) secador
solar con extractor de aire y calefactores con energía solar, fueron
comparados con el secado tradicional (T0) (piso de cemento). Se evaluó
tiempo de secado, defectos físicos del grano, rendimiento, calidad
sensorial y microbiológica. Los mejores resultados se obtuvieron en
el P3 con un tiempo de secado de 52 h (2 días ¼), con granos de café
pergamino seco sin defectos primarios, mayor rendimiento en café
oro exportable (83,24 %), perl sensorial de 84,25 puntos calicado
como café especial grado Q Premium y mejor inocuidad que el café
obtenido por secado tradicional; demostrando que el secador solar
tipo invernadero con extractor de aire y calefactores con energía solar
es una alternativa sostenible para mejorar la eciencia del secado del
café preservando su calidad sensorial, valor imprescindible para que
los productores logren mejores precios.
Palabras clave: cafés especiales, invernadero, catación, sensorial,
inocuidad.
Resumo
A redução do tempo de secagem do café sem efeitos negativos
na qualidade da chávena tem sido objeto de vários estudos de
investigação. O objetivo era determinar o efeito de três variantes de
um protótipo de secador solar de estufa na qualidade física, sensorial
e microbiológica do café. O protótipo de secador solar com três
variantes, o protótipo 1 (P1) secador solar de estufa, o protótipo 2
(P2) secador solar com extrator de ar e o protótipo 3 (P3) secador
solar com extrator de ar e aquecedores solares, foi comparado com a
secagem tradicional (T0) (chão de betão). Foram avaliados o tempo
de secagem, os defeitos físicos do grão, o rendimento, a qualidade
sensorial e microbiológica. Os melhores resultados foram obtidos em
P3 com tempo de secagem de 52 h (2 ¼ dias), com grãos de café
pergaminho secos sem defeitos primários, maior rendimento em café
ouro exportável (83,24 %), perl sensorial de 84,25 pontos qualicado
como café especial (com grau Q Premium) e melhor segurança que
o café obtido por secagem tradicional; demonstrando que o secador
solar tipo estufa, com extrator de ar e aquecedores de energia solar,
é uma alternativa sustentável para melhorar a eciência da secagem
do café, preservando sua qualidade sensorial, valor essencial para os
produtores alcançarem melhores preços.
Palavras-chave: cafés especiais, estufa, degustação, sensorial,
segurança.
Introduction
Currently coee producers are looking for new processing
techniques to improve their quality and achieve dierentiated sensory
proles for international markets (Osorio et al., 2022), according to
the same author, after harvesting the coee cherries, they are pulped,
fermented and washed, immediately followed by drying, dehydrating
the bean until it reaches a humidity that guarantees its conservation
and stability. This process can be carried out mechanically, in raised
beds or patios in order to reduce humidity to 10 to 12 %, thus
obtaining a more stable product in storage (Torres-Valenzuela et al.,
2019). Traditional drying in cement patios or blankets directly to
the ground take advantage of solar energy that is often varied due
to climatic conditions (Prada et al., 2019), as often occurs in the
central rainforest of Peru, with unexpected rains or prolonged periods
of shade; also, large drying yard areas and personnel are needed to
remove the layer of coee, collect at sunset, cover the beans with
plastic, spread them out the next day and control the drying, under
the risk of loss of quality due to slowness in the process; as well as
contamination with dust, fungi and the presence of animals that aect
the safety of the dried beans (López and Chávez, 2018).
An alternative solution is to dry the coee inside a solar dryer,
which produces coee beans with fewer defects (stains), ensuring
greater safety and better sensory quality (Quintanar and Roa, 2017).
In addition, this process contributes to using less space because they
have shelves and drying beds (parihuelas), with plastic covers to
avoid the collection of grains when it rains, reduce contamination due
to the eect of trampling by operators or animals (Briceño-Martínez
et al., 2020), obtaining an uneven drying if constant movements are
not made to the mass of coee and control of the high temperatures
reached in the interior (Cruz et al., 2010).
The quality of dried parchment coee depends on the variety
grown, environmental conditions, agronomic practices, processing
method, storage conditions (Tolessa et al., 2018), industrial processing
and the nal preparation of the beverage (Pabón and Osorio, 2019),
interrelated characteristics that when modied can favor or deteriorate
the sensory characteristics of the beverage (Ramos and Criollo, 2017).
Therefore, the drying process of coee beans is crucial to preserve the
physical and sensory characteristics of the bean and the nal product
(Guevara-Sánchez et al., 2019).
Due to the lack of uniformity in the quality of the coee lots dried
on cement oors at the Cooperativa Agraria Cafetalera Perené (CAC
Perené), which has 280 active members, for whom, at harvest time, the
drying lines are insucient and do not guarantee uniform quality or
the safety of the beans, a solar greenhouse prototype was implemented
with appropriate technology under dierent conditions for its proper
operation and use. In this dryer, both the air extractor and the heaters
work with photovoltaic cells, taking advantage of solar energy. This
isolated system requires a power bank and is used where the electrical
grid does not reach, which is currently expensive. The construction
of this type of dryer had the primary purpose of serving all partners,
seeking to improve the quality of coee; due to the fact that, specialty
coees with high levels of cup requirement (> 84 points) are more
required in the world market (Guevara-Sánchez et al., 2019). The
use of solar energy accumulated in batteries was also prioritized to
supply the extractors and heaters that operate at night, as indicated
by the Sustainable Development Goals of the United Nations (United
Nations, 2018). These variants were tested in the greenhouse type
solar dryer, since there are no references of the adaptations in this
type of dryer. The reduction in drying time contributes to a greater
number of producers beneting from this drying system, having more
time available for other activities, as well as making their coee lots
more uniform in order to achieve better prices. In this context, the
objective of this research was to determine the eect of three variants
of a prototype greenhouse solar dryer on the physical, sensory, and
microbiological quality of dried parchment coee.
This scientic publication in digital format is a continuation of the Printed Review: Legal Deposit pp 196802ZU42, ISSN 0378-7818.
Huamán-Murillo et al. Rev. Fac. Agron. (LUZ). 2024 40(2): e2441123-6 |
Materials and methods
Location and raw material
The study was carried out in the town of Marankiari, district of
Perené, Province of Chanchamayo, Junín region, central Peru, at the
CAC Perené. Catimor and Colombia varieties of coee harvested
between June and July 2021 were used.
Variants of the greenhouse-type solar dryer prototype
The technical characteristics of the prototype were designed
by engineers contracted by CAC Perené as part of project PIMEN-
10-P-040-144-15. The three variants in the drying prototype
constituted the levels/factor under study, which are described below:
Prototype 1
Greenhouse type solar dryer with ventilators in the basal part
(sliding doors) all covered with transparent and UV resistant plastic,
oval shaped; dimensions 10 m wide, 20 m long and 6 m high; inside
which were installed two-story table type parihuelas with dimensions
of 1.50 m high, 4 m long, 1.50 m wide; 1 m separation height of the
second oor, 50 cm separation of the second oor parihuelas; with
structure of metal tubes of 3.54 cm in diameter.
Prototype 2
The rst prototype was additionally tted with a humid air
extractor at the top of the dome; this equipment works with energy
accumulated by the solar panel, which used an energy converter and
a battery system for its storage.
Prototype 3
The second prototype was tted with internal heating equipment
such as incandescent lamps that operated at night with energy
accumulated by the solar panels.
Methodology
The experiment was carried out according to the following stages:
Obtaining the oreado parchment coee: The cherry coee beans
(470 kg) were pulped, fermented and washed, for their transfer they
were lled in ventilated woven raa sacks (280 kg). The coee was
transported from the plots in the dierent zones of the Perené district
located at altitudes of 1000 to 1200 m.a.s.l. to the town of Marankiari
where the prototype greenhouse-type solar dryer was installed. Travel
time was approximately 6 hours.
Drying
It was carried out in the three variants of the prototype, the air-
dried grains were placed in the drying racks inside the dryer (15 kg per
treatment/repetition), data on time, weight, temperature and humidity
were taken every 2 hours, turning the grains at the same time. The
traditional sun drying (T0) also used dried coee beans (15 kg per
repetition), it was carried out on a cement oor with dimensions of
15 m x 10 m, which, because they were exposed to the environment,
at night at 19 hours the beans were collected in mounds and covered
with plastic, then at 07 hours the next day they were spread out again
to continue drying, this was repeated until the desired humidity was
reached; this process is the traditional way in which the members of
the CAC Perené carried out the drying process.
Packaging
The dried parchment coee beans that came from the variants and
traditional sun drying were packaged in jute sacks, coded according
to the treatments under study.
Quality control
Samples of 350 g of each treatment were taken and physical,
sensory and microbiological evaluations performed in triplicate.
Analysis of fresh roasted coee and dry parchment coee
Moisture in the fresh coee was determined by the
thermogravimetric method and in the dry beans with a Wile Coe
®
moisture meter with direct reading; acidity was determined by
titration with NaOH 0.1 N in fresh coee expressed as lactic acid and
in dry coee as malic acid, and pH with a digital potentiometer.
Controls during the process
The temperature and relative humidity data were measured during
the drying time with six digital thermohygrometers, located four at
the ends of the dryer and two in the middle part. The sun-drying
temperature was determined with two digital thermohygrometers
located on the coee beans.
Analysis of dry parchment coee
Number of defects and/or contaminants. The equivalences of
defects described in the SCA (Specialty Coee Association) manual
were used, which dierentiates between category 1 or primary defects
and category 2 or secondary defects. Each type of defect was counted
individually; according to the manual, if two simultaneous defects
Figure 1. Day and night view of the prototype used in the research.
This scientic publication in digital format is a continuation of the Printed Review: Legal Deposit pp 196802ZU42, ISSN 0378-7818.
Rev. Fac. Agron. (LUZ). 2024, 41(2): e244112 April-June. ISSN 2477-9407.4-6 |
are found, the one with the greatest impact is taken into account; bean
malformations are not defects (SCA, 2019).
Yield factor
This value was obtained by dividing the weight of gold coee by
the weight of dry parchment coee, adjusted to a reference humidity
percentage (12 %).
Sensory analysis
It was performed with a certied Q grader cupper following the
preparation and analysis protocols according to the SCA standard
(2003), with three repetitions per sample, the attributes evaluated
were: Fragrance/Aroma, Flavor, Residual Flavor, Acidity, Body,
Balance, Uniformity, Clean Cup, Sweetness and Taster Score; the
nal result was expressed on a scale of 0 to 100 points; with the range
of 90 to 100 being considered exceptional, 85 to 89.9 excellent, 80 to
84.9 very good with description of special, and < to 80 below special
quality (SCA, 2015).
Microbiological analysis
In addition to mold counts, yeasts, Escherichia coli and
mycotoxins (Ochratoxin A) were also determined.
Statistical analysis
With the results of the physical and sensory characteristics,
analysis of variance was performed in a complete randomized design
with three replications. In the variables that presented signicant
dierences, the Tukey test was performed at 5 %.
Results and discussion
Physicochemical characteristics of fresh and dry coee bean
The humidity of freshly washed coee is 53 %, which is reduced
during air-drying to 48.8 % (surface drying of the parchment). The
humidity of dried beans does not show signicant dierences, the
overall average being 11.72 % (table 1), an acceptable average for
storing the product, preserving its quality (Prada et al., 2019) and
stability (Osorio et al., 2022). According to Gallego and Rodriguez
(2021), dry coee beans should have a humidity between 10 and 12
%, to be stored for up to 10 months. The acidity and pH of the beans
do not show signicant dierences either, with averages similar to
those reported by (Camargo Caysahuana and Contreras Rodríguez,
2020). In this regard, López et al. (2015) observed a decrease in pH
during fermentation, which can inuence coee quality, therefore,
(Juárez et al., 2021) highlights the importance of fermentation control
in the production of high quality coee.
These studies highlight the importance of monitoring and
controlling the pH and acidity of coee during the fermentation and
drying processes.
Controls of time, temperature and humidity during drying
process
Table 2 shows that the drying time of parchment coee beans in
prototype 1 (greenhouse type solar dryer) was 112 hours (approx. 5
days), in prototype 2 with humid air extractor it was 58 hours (approx.
2 ½ days), in prototype 3 with humid air extractor and heaters during
the night it was 54 hours (approx. 2 ½ days) and in the traditional
drying it was 124 hours, considering that only 12 hours were dried,
from 7:00 am to 7:00 pm which is equivalent to 9 days. 2 days and
¼) and in the traditional drying was 124 hours, considering that only
12 hours were dried, from 7:00 am to 7:00 pm which is equivalent
to 9 days, evidencing that the drying time is reduced when the air
extractor and incandescent lamps work in prototype 3; the traditional
drying time is similar to that performed in the valley of Alto Mayo,
San Martin region in Peru at an altitude of 873 m.a.s.l. (Guevara-
Sánchez et al, 2019). Inside the dryer temperatures are higher and
are possible to control as well as relative humidities when using the
air extractor, in this regard (Prada et al., 2019) and (Quintanar and
Roa, 2017) found that solar dryers with continuous air ow systems,
powered by photovoltaic energy, are eective in reducing coee
drying time, with better control of relative humidity and temperature.
In the present research, using the variants of the prototype, shorter
drying times were achieved while preserving the intensity of the
bean’s acidity and consequently its cup quality.
Table 1. Physicochemical analysis of wet and dry parchment coee beans.
Component Fresh roasted coee
Dry coee
Prototype 1 Prototype 2 Prototype 3 Traditional drying
Humidity (%) 48.80 ± 0.35 11.84 ± 0.14
a
11.79 ± 0.10
a
11.69 ± 0.11
a
11.60 ± 0.10
a
Acidity (%) 0.20
*
± 0.03 1.26
**
± 0.06
a
1.24
**
± 0.14
a
1.19
**
± 0.09
a
1.29
**
± 0.06
a
pH 4.50 ± 0.18 6.19 ± 0.19
a
6.21 ± 0.19
a
6.25 ± 0.14
a
5.98 ± 0.10
a
Note: *Expressed in lactic acid, **Expressed in malic acid.
Table 2. Time, temperature and relative humidity during drying process.
Type of dryer
Drying time
(h)
Drying condition
T (°C) HR (%)
Prototype 1 112.05 ± 0.94
d
58.04 ± 0.96
c
67.03 ± 1.67
c
Prototype 2 58.04 ± 1.05
b
50.04 ± 1.29
b
63.04 ± 0.51
b
Prototype 3 54.07 ± 0.60
a
50.00 ± 0.64
b
60.03 ± 1.17
a
Traditional drying 124.00 ± 1.20
c
40.05 ± 0.92
a
75.03 ± 1.62
d
Defects number in dried grains
No primary defects were found in any of the prototype variants,
but in traditional drying, partially sour kernels (2 defects), which
according to SCA (2019) occurs after harvesting and foreign matter
(stones and sticks, 2 defects) due to drying in yard. Secondary defects
were only found in prototype 1 (2 defects: oating kernels and shell
kernels), while in traditional drying 13 defects: oating beans, shell
beans and split beans due to mechanical damage caused by the use
of wooden trackers used in the coee storage operations at night;
demonstrating that with the prototypes the number of defects was
reduced improving the quality of the coee, in this regard, SCA
(2015) points out that special coees in green gold bean meets
Dierent letters indicate signicant dierences obtained by Tukey’s mean comparison test (P≤0.05).
This scientic publication in digital format is a continuation of the Printed Review: Legal Deposit pp 196802ZU42, ISSN 0378-7818.
Huamán-Murillo et al. Rev. Fac. Agron. (LUZ). 2024 40(2): e2441125-6 |
exceptional physical characteristics in terms of granulometry and
reduced presence of defects, and to be considered green gold coee
Special Grade must have maximum 5 secondary defects and no defect
category 1 (primary) in 350 g; the results obtained show that in the
variants of the greenhouse type dryer all the beans are of Special
Grade, which is not the case with the traditionally dried beans, which
presented primary and secondary defects; therefore, the use of the
variants of the dryer allowed a better control of the drying process
avoiding the majority of defects.
Parchment to gold yield
In Table 3, it can be seen that there is a signicant dierence in
the yield of gold coee, with prototype 3 having the best yield factor
0.833 and a yield in exportable gold coee of 83.24 %; in this regard,
when a coee has more than 74 % of healthy kernel, coee growers
receive an incentive for quality (Gamboa et al., 2015), therefore, with
the use of the solar dryer prototype in all variants it is possible to
obtain a better yield and beans of better physical quality with fewer
defects.
Sensory analysis of dry beans
Table 4 shows that the best results were obtained in prototype
3, followed by prototype 2, with no signicant dierences between
them; in prototype 1 and in the traditional drying process lower scores
were obtained; in the dried coees in the prototypes sweet notes, citric
acidity, smooth body, smooth aftertaste, clean coee were found;
while in the traditional drying process notes of sweet chocolate, light
Table 3. Parchment to gold coee yield and yield factor (YF).
Type of dryer
Parchment weight Gold coee (exportable) YF
g % Weight (g)
Prototype 1 350 80.20 280.70
b
± 1.58 0.802
Prototype 2 350 80.56 281.97
b
± 4.23 0.806
Prototype 3 350 83.24 291.33
a
± 1.50 0.833
Traditional drying 350 78.72 275.50
b
± 3.51 0.787
Note: YF is a coecient that multiplied by the initial parchment weight (adjusted to a reference percentage of humidity (12 %) gives the weight in gold coee.
acidity, light body, astringency and bitter aftertaste were found. In
the prototypes the nal scores are above 82 points, which according
to the classication (SCA, 2015) from 80 to 84.99 corresponds to a
Very Good - Specialty coee. Therefore, in the evaluated prototypes,
in addition to preserving the sensory quality, it reduced the drying
time, protecting the beans from external agents and with less presence
of primary defects, demonstrating that with prototype 3 beans with
optimal physical and sensory quality are obtained (84.25 points) for
marketing how specialty coee and achieve better prices; similar to
that achieved by Juarez et al. (2021) in specialty coee with 84 points,
and Gallego and Rodriguez (2021) in coee with special quality with
81.3 points.
Microbiological analysis in dried parchment coee
In addition to the determination of molds in coee beans referred
to by INACAL (2021), in order to verify the safety conditions of the
beans, the numbering of yeasts and Escherichia coli has also been
determined; in all the variants of the prototype, the values determined
were below this limit; but in the case of coee obtained by traditional
drying, when the presence of molds was found, the determination of
Ochratoxin A was carried out, whose maximum permissible level is
10 ng.g
-1
(ppb) (NTP 209.320, 2021); in the investigation, the results
were not detectable (N.D.), therefore, even when molds were found
in the coee beans dried in the sun on a cement oor, the presence of
Ochratoxin A has not been detected (table 5).
Table 4. Sensory prole of green gold coee beans.
Attribute P1 P2 P3 T0
Fragrance/ Aroma 7.50 7.75 7.75 6.00
Flavor 7.50 7.75 7.75 7.00
Residual Flavor 7.25 7.75 7.75 7.25
Acidity 7.50 7.75 7.75 7.25
Body 7.25 7.50 8.00 7.25
Balance 7.50 7.50 7.75 7.50
Uniformity 10.00 10.00 10.00 10.00
Clean Cup 10.00 10.00 10.00 10.00
Sweetness 10.00 10.00 10.00 10.00
Tasting Point 7.50 7.50 7.50 7.25
Averages 82.00
c
± 0.25 83.50
a.b
± 0.25 84.25
a
± 0.25 79.50
d
± 0.50
Dierent letters indicate signicant dierences obtained by Tukey’s mean comparison test (P≤0.05).
This scientic publication in digital format is a continuation of the Printed Review: Legal Deposit pp 196802ZU42, ISSN 0378-7818.
Rev. Fac. Agron. (LUZ). 2024, 41(2): e244112 April-June. ISSN 2477-9407.6-6 |
Conclusions
In the greenhouse type solar dryer with air extractor and heaters
(P3) the drying time of coee was reduced from 9 days to 2 ¼ days,
achieving dry parchment coee beans, without primary defects, with
a higher percentage of exportable coee (83.24 %), a sensory prole
of 84.25 points and with better safety than in traditional drying; in
addition, it has advantages over traditional drying and similar solar
dryers, because it works day and night using renewable energy
generated by solar panels; and by drying a greater quantity in a smaller
space it benets a greater number of members of the CAC Perené in
obtaining coee with good cup quality and free of contaminants.
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Table 5. Microbiological results of coee beans.
Type of dryer
Molds Yeast E. coli Ochratoxin A
UFC.g
-1
UFC.g
-1
NMP.g
-1
µg.kg
-1
(*)
Prototype 1 ˂ 10 ˂ 10 ˂ 3 --
Prototype 2 ˂ 10 ˂ 10 ˂ 3 --
Prototype 3 ˂ 10 ˂ 10 ˂ 3 --
Traditional drying 25x10
2
˂ 10 ˂ 3 N.D.
Note: The determination of ochratoxin A was performed only in coee from traditional drying because the presence of mold was detected.