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CORADI, P. C. et al.
38
Coffee Science, Lavras, v. 2, n. 1, p. 38-47, jan./jun. 2007
EFFECT OF DRYING AND STORAGE CONDITIONS ON THE QUALITY
OF NATURAL AND WASHED COFFEE1
Paulo Carteri Coradi
2
, Flávio Meira Borém
3
, Reni Saath
4
, Elizabeth Rosemeire Marques
5
(Recceved: september 25, 2006; accepted: february 27, 2007)
ABSTRACT:
The objective of the work was to evaluate alterations in the quality of natural and washed coffee under different drying
conditions (coffee drying yard, temperature of 40ºC and 60ºC) and storage conditions at 60% of relative humidity, with controlled
temperature of 23ºC, at 90 and 180 days. The work was carried out in the Engineering Department and in the Coffee Post-Harvest
Technology Pole of the Federal University of Lavras. The manual harvest of the coffee (Coffea arabica L.), Topázio variety, was
selective. Part of the coffee was pulped and the other part was processed in the natural form. A portion of each type of coffee was
submitted to drying on the yard and two other samples were processed in a mechanical dryer, at temperatures of 40ºC and 60ºC. After
drying, the coffee was stored in an air-tight room, in which a stable relative humidity of 60% was maintained with a solution of
magnesium nitrate. Quality evaluation, sensorial analyses, electric conductivity and potassium leaching tests, total titrable acidity,
fatty acidity and total and reducing sugars determinations were carried out. The results showed that the coffee dried at 60ºC, after 90
days storage, presented the poorest quality. The physical-chemical evaluations of the drying and storage conditions showed that
washed coffee presents better quality when compared to the product in its natural form.
Key words:
Coffea arabica
, drying, storage, quality.
EFEITO DAS CONDIÇÕES DE SECAGEM E ARMAZENAMENTO SOBRE
A QUALIDADE DO CAFÉ NATURAL E DESPOLPADO
RESUMO:
Objetivou-se com o presente trabalho avaliar as alterações na qualidade dos cafés natural e despolpado nas condições
de secagem (terreiro, temperatura de 40ºC e 60ºC) e armazenamento de 60% de umidade relativa com temperatura controlada de
23ºC, aos 90 e 180 dias. O trabalho foi realizado no Departamento de Engenharia e no Pólo de Tecnologia em Pós-Colheita do Café
da Universidade Federal de Lavras. A colheita manual do café (Coffea arabica L), variedade Topázio, foi seletiva. Parte do café foi
despolpado e outra parte, processada de forma natural. Uma parcela de cada tipo de café foi submetida
à secagem em terreiro e as
outras duas, às temperaturas de 40ºC e 60ºC em secador mecânico. Depois da secagem, o café foi armazenado em ambiente
hermético, mantendo-se constante a umidade relativa de 60%, com solução de nitrato de magnésio. Para avaliação da qualidade,
foram realizados análise sensorial, testes de condutividade elétrica e lixiviação de potássio, determinações de acidez titulável total,
acidez graxa, açúcares totais e redutores. Pelos resultados obtidos, conclui-se que os cafés submetidos à secagem com temperatura
de 60ºC e armazenados a partir de 90 dias apresentaram as piores características de qualidade; as avaliações físico-químicas para
as condições de secagem e armazenamento mostram que o café despolpado apresentou melhor qualidade, quando comparado com
o produto na sua forma natural.
Palavras-chave: Coffea arabica, secagem, armazenamento, qualidade.
1
Trabalho apresentado no 32º Congresso Brasileiro de Pesquisas Cafeeiras – 24 a 27 de outubro de 2006 – Poços de Caldas – MG.
2Engenheiro Agrícola, MS, Doutorando em Engenharia Agrícola da Universidade Federal de Viçosa/UFV – Viçosa, MG –
paulocoradi@yahoo.com.br
3
Professor Associado – Universidade Federal de Lavras/UFLA – Departamento de Engenharia Agrícola – Cx. P. 3037 – 37200-000 –
Lavras, MG – flavioborem@ufla.br
4
Engenheira Agrícola – Mestranda em Engenharia Agrícola – Universidade Federal de Lavras/UFLA – Cx. P. 3037 – 37.200-000 –
Lavras, MG – reniagricola@ufla.br
5
Agronôma, MS, Universidade Federal de Lavras/UFLA – Cx. P. 3037 – 37.200-000 – Lavras, MG – bethagropetagro@yahoo.com.br
1 INTRODUCTION
Coffee (Coffea arabica L) production in
Brazil has increased significantly in the last few
decades, with an increase of the production areas
and the utilization of new technologies. The greatest
difficulty found in the coffee production chain today
is its great variation of prices (PINTO, 2006).
Producing high qu
ality coffee in Brazil is not only a
demand but an opportunity for the sector and a decisive
factor also in the product’s exportation.
Brazilian coffee exportation has been
decreasing in the past decades, due partly to the
increase of coffee pro
duction in other countries, but
also to the poor quality of the Brazilian product sold
39
Effect of drying and storage conditions on the quality...
Coffee Science, Lavras, v. 2, n. 1, p. 38-47, jan./jun. 2007
in the external markets. The growing demand for
quality, associated to the reduction of production costs,
are stimulating both producers and researchers to
develop new technologies more suited to the
productive system.
Coffee’s commercial quality is associated to a
set of factors that involve physical-chemical and sensorial
aspects which, in turn, depend on the products’ drying
and storage conditions (AFONSO JÚNIOR, 2001;
NOBRE
, 2005). During the drying process, variations
in the structure of the beans (color, aspect, defects,
buquet and fl
avor, etc) can occur, affecting the quality
of the beverage. External factors, such as temperature,
relative humidity and mechanical damage can alter the
structure of the membranes, leading to a loss of their
organization and
selectivity (
AMORIM
et al., 1978),
reducing coffee’s quality potential.
Corrêa et al. (1994), Sfredo et al. (2005) e
Souza (2000), studying coffee drying, concluded that,
to obtain a good quality product and a soft beverage,
the drying temperature must be maintained around
40º C. However, to preserve coffee’s initial qualities,
correct drying is not enough. The adequate storage
is also important.
In order to store coffee for longer periods of
time and maintain its initial chemical, physical and
sensorial characteristics, the temperature and the
relative humidity of the environment must be
monitored. A
fonso Júnior (2001) observed a decrease
in the composition of reducing sugars in coffee beans
and grains as storage time in higher relative humidity
conditions increased.
Considering the effect of drying and storage
on the quality of coffee pre-processed in different
ways, the objective of this work was to evaluate
alterations in the quality of natural and washed coffee
submitted to different drying conditions (yard,
temperature of 40ºC a
nd 60ºC) and stored at 60% of
relative humidity, with controlled temperature of 23ºC,
for 180 days.
2 MA
TERIAL
AND METHOD
Location of the experiment
The work was carried out in the Engineering
Department and in the Coffee Post-Harvest
Technology Pole of the Federal University of Lavras,
state of Minas Gerais, in Brazil.
Coffee pre-processing
The coffee was harvested manually and only
the cherry beans were removed from the plant. For
the three repetitions, 2400 L of coffee, Topázio variety,
were harvested. For each repetition, 150 L of coffee
cherry beans were spread directly on the yard,
constituting the natural coffee portion, and another
150 L were separated for mechanical drying. To obtain
the washed coffee, 500 L of coffee cherry beans
were used. The coffee was pulped in a fermentation
tank, where it was revolved for 20 hours. A sample
of the pulping water was collected to determine pH
and temperature, in order to avoid fermentation
problems and interferences in the coffee’s quality.
After 20 hours, the coffee was washed to remove
the mucilage
and pre-dried.
Drying
After pulping, a portion of the coffee was pre-
dried on a yard, where it remained for 1 day, and
then placed in a mechanical drier. The remaining
portion continued drying on the yard until 11% (wet
basis). The natural coffee was also pre-dried on a
yard, but for a period of 2 days. During drying on the
yard, both the washed (8 days) and the natural coffee
(13 days) were revolved every half-hour during the
day (8 hours per day) and the temperature and relative
humidity were monitored using a thermohigrograph.
At night, the coffee was placed on trays in thin layers
and protected from the effects of temperature and
relative humidity.
Mechanical drying was done in two fixed layer
prototypes with electrically heated air. To obtain air
flow a diaphragm with a controled opening at the
entrance of the fan was used. The average speed
of
the air was measured using a digital anemometer with
rotating blades at the entrance of the drying chamber.
The air flow was regulated at 20m³min
-
¹m
-
².
During drying, the temperature of the coffee
grains, the environmental temperature and the relative
humidity of the air were measured periodically. The
temperature of the coffee grains was measured every
30 min using type J thermocups placed at the center
of the granular mass in each division of the drying
chamber. To minimize any possible differences in
temperature between the four divisions, due to the
positioning of the electric resistances in the plenum,
CORADI, P. C. et al.
40
Coffee Science, Lavras, v. 2, n. 1, p. 38-47, jan./jun. 2007
the apparatuses containing the samples were rotated
every hour until drying of 11% (wb).
The samples used to determine the water
content of the coffee in the yard were taken at the
end of the morning and of the afternoon during the
first 5 days, and then daily at the end of the
afternoon. To determine the water content of the
coffee in the mechanical drier, 100g samples were
taken every hour. The water content was
determined by the oven method at 105 +
3ºC
(
BRASIL
, 1992), until 11% (wb). A digital G-800
model moisture measurer was used to determine
when to interrupt drying (11%
wb).
Storage
Once drying was interrupted at 11% (wb) of
humidity, the coffee in the drier was cooled and
conditioned in 5 kg jute bags and later hermetically
stored in a container. The cooling process was not
repeated with the coffee in the yard due to the low
temperature in the granular mass. During the whole
storage period, relative humidity was controlled at
60% and temperature was maintained at 23ºC.
To maintain storage temperature at 23ºC air
conditioning, regulated accordingly, was used. To
control the relative humidity, a salt solution
(magnesium nitrate, Mg (NO
3)2
) was used (Dhingra
& Sinclair, 1995)
.
The air inside the storage system
circulated continuously in a closed system, passing
through the grains and the magnesium nitrate until
they were in balance. This condition remained
constant throughout the whole storage period.
Temperature and relative humidity were
measured daily in the morning during the 6 months of
storage. To measure and control the storage system
(humidity and temperature) a digital thermohigrometer
model Higrotemp 90 was used.
Charactetization of coffee quality
Sensorial analysis
The sensorial analysis of the coffee was
carried out at the Monte Alegre S/A farm in Alfenas,
MG. Coffee samples of 300g were prepared, for each
repetition, by removing the defective beans
. The
samples were coded and analyzed by three qualified
tasters of the “Brazil Specialty Coffee Association”
(BSCA).
The methodology used was the “Cup of
Excellence” (CoE), suggested by Howell (1997), in
which each sensorial attribute (body, aroma, acidity,
sweetness, balance and characteristic flavor) received
a score according to its intensity in the samples,
making this methodology more objective than cup test.
For each sensorial attribute the samples received a
score on a scale of 0 to 8 (BSCA, 2006).
The tasters evaluated the coffee’s buquet in
three parts: dry powder, crust and infusion and noted,
in a space reserved for personal observations, the
nuances and distinct aromas observed. The attributes
clean beverage, sweetness, acidity, body, flavor,
remnant flavor, balance and general score were then
evaluated, resulting in a final score count that indicated
the higher and poorer quality coffees.
Electric conductivity
The electric conductivity of the raw beans was
determined by adapting the methodology
recommended by Kryzyanowski et al. (1991). Fifty
beans with no visible defects from each sample were
used. The beans were weighed (0,001g precision) and
immersed in 75 mL of deionized water inside plastic
cups with a capacity of 180 mL. These recipients
were placed in a ventilated oven regulated to 25ºC
for 24 hours. The solution’s electric conductivity was
measured by the CD-20 Digimed apparatus. From
the results obtained, electric conductivity was
calculated and the results were expressed in ìS cm
-
¹ g
-¹
of sample.
Potassium leaching
Potassium ion leaching in the raw beans was
done according to the methodology proposed by Prete
(1992). After the electric conductivity readings, the
amount of leached potassium ions in the solutions was
determined. This reading was done in a Digimed NK-
2002 flame photometer. With the data obtained, the
potassium leached was calculated and the result was
expressed in ppm/g.
Total titrable acidity
The total titrable acidity was determined by
titration with NaOH 0,1 N, adapting the methodology
cited by AOAC (1990). 50 mL of distilled water were
added to 2 g of ground sample coffee and the solution
was revolved for 1 hour. The solution was then filtered
41
Effect of drying and storage conditions on the quality...
Coffee Science, Lavras, v. 2, n. 1, p. 38-47, jan./jun. 2007
using a paper filter and 5 mL were mixed in an
erlenmeyer with 50 ml of distilled water. 3 drops of
phenolftalein were added and the solution was titrated
until turning point with NaOH 0,1N. The results were
expressed in mL of NaOH 0,1 N per 100g of sample.
Fatty acidity
Fatty acidity was determined by titration
according to the 02-02 A or quick fatty acidity method
described by the AACC (1995). 40 g of the ground
sample coffee were weighed, dissolved in 100 mL of
toluene and shaken for 1 hour and 30 minutes. The
solution was then filtered. In a bequer, 25 mL of the
filtered solution were mixed with 25 mL of alcohol
and ph
enolftalein. The solution was titrated with KOH
until reaching the turning point. The fatty acidity results
were expressed in mL of KOH per 100g of dry matter
(DM), calculated according to equations 1 and 2.
DM = (1 - M (db)) x 40g
where:
DM – mass of dry sample (g);
M (db) – dry base moisture content
V x 100
FA =
DM
equation 1
equation 2
where:
V – volume of KOH used to titrate the solution
(extract + indicator) in mL;
FA – fatty acidity (mL of KOH/100 g of dry matter).
Total and reducing sugars
The total and reducing sugars were extracted
according to the Lane-Enyon method described by
the AOAC (1990). The values were expressed in
percentage.
Treatments and statistical design
The statistical design used was a split-plot
in
time, in a 2 x 3 x 3 factorial scheme with three
repetitions. The treatments correspond to two types
of coffee (natural and washed), three drying systems
(yard, temperatures of 40 ºC and 60ºC) and three
storage periods (0, 90 and 180 days).
The data obtained were analyzed by the Sisvar
4.0 computer program, according to Ferreira (2000)
and the means were compared through the Tukey
test.
3 RESUL
TS
AND DISCUSSION
The mean temperature and relative humidity
values at the start of the drying process in the
mechanical driers and the initial and final water
content of the coffee dried on the yard and at 40ºC
and 60ºC for each treatment, in the three repetitions,
are presented in Table 1.
The mean temperature and relative humidity
values refer to the mean values collected daily during
mechanical drying with the air in the coffee grains
heated to 40ºC and 60ºC. Table 1 shows that the mean
relative humidity and temperature values were similar
in all the tests, varying from 49% to 61% (wb) and
from 20,23ºC to 23, 43ºC, respectively. The
temperature and relative humidity values for drying
on a yard varied from 20,53ºC to 24,1ºC and 46% to
66% (wb), respectively, in all the repetitions.
Table 1 shows that the initial water content of
washed coffee varied from 50,78% to 57,66% (wb)
and that, after drying, the water content was 10,15%
(wb). The water content of natural coffee, at the
beginning of the drying process, varied from 58,60%
to 65,60% (wb), arriving finally at the mean storage
level of 12% (wb).
Before drying at 40ºC and 60ºC, the washed
coffee was pre-dried on a yard for 1 day and the
natural coffee for 2, so that both would begin drying
in the same conditions, losing, in average, 5% of their
moisture content. The natural coffee began drying in
the drier with a water content varying from 43,08%
to 50,95% (wb), reaching mean storage level at
11,03% (wb). The washed coffee started out with
moisture content around 38,71% to 40,42% (wb),
reaching mean storage level at 10,56% (wb).
The mean temperature and relative humidity
values during storage of washed and natural coffee
dried on a yard and at 40ºC and 60ºC are presented
in Table 2.
Table 2 shows that, during the storage period,
the temperatures at the beginning and ending of
storage remained between 22,8ºC and 23,5ºC, varying
on average 0,7ºC. The relative humidity in storage
remained between 63,8% and 64,6% for the
equilibrium condition of 60% of relative humidity.
These results are similar to those found by Afonso
CORADI, P. C. et al.
42
Coffee Science, Lavras, v. 2, n. 1, p. 38-47, jan./jun. 2007
Table 1 –
Mean values of the product and surrounding air conditions in all the treatments, in the three repetitions.
Moisture content (% wb)
Average air condition at the
entrance of the drier and yard
Repetitions
Coffee
Processing
Drying
processing
temperature
(ºC)
Initial
Final
Temperature.
(ºC)
RH
(%)
Washed
41,34
11,35
20,76
61
Natural
60
50,
11
11,15
20,76
61
Washed
41,34
12,00
20,23
59
Natural
40
50,95
12,22
20,23
59
Washed
50,78
9,33
24,10
46
I
Natural
Yard
61,38
11,79
23,51
50
Washed
40,12
9,33
21,54
55
Natural
60
43,08
9,49
21,54
55
Washed
38,71
11,12
21,89
54
Natural
40
43,87
12,22
21,89
54
Washed
51,97
10,74
21,34
57
II
Natural
Yard
58,60
12,94
22,42
56
Washed
41,76
9,12
23,22
49
Natural
60
45,72
11,81
23,22
49
Washed
40,42
11,27
23,43
51
Natural
40
46,07
12,57
23,43
51
Washed
57,66
11,04
20,53
66
III
Natural
Yard
65,60
11,65
21,50
58
Table 2 –
Mean temperature and relative humidity values
obtained during 180 days of storage.
Storage temperature
Relative humidity 60%
Entrance
Exit
Entrance
Exit
22,8 ºC
23,5ºC
63,8%
64,6%
Júnior (2001), who evaluated the equilibrium moisture
content of parchment, washed and harvested coffee.
The electric conductivity and potassium
leaching values, due to the effects of the different
drying, pre-processing and storage processes, are
presented in Tables 3 and 4.
As shown in Tables 3 and 4, in most of the
storage and pre-processing combinations, the electric
conductivity and potassium leaching values increased
significantly (P<0,05) as the temperature of drying
increased (Table 1). According to Prete (1992),
coffee’s deterioration and quality loss is directly
related to the higher potassium leaching values that
occur due to the degeneration of the cellular
membranes (
LIN
, 1988; MARCOS FILHO et al.,
1990; SCHOETTLE & LEOPOLD, 1984;
WOODSTOCK
, 1973).
The highest electric conductivity and potassium
leaching values, independent of drying and pre-
processing, were found for the longer storage periods.
Despite the 60% relative humidity conditions
recommended for storing agricultural products, at 180
days high electric conductivity and potassium leaching
values were observed, corroborating the results found
by Coelho et al. (2001) and Silva et al. (2001). Amorim
(1978), studying water absorption in beans stored at
60% of relative humidity, observed a greater metabolic
activity, which lead to the deterioration of the coffee
and a loss of its quality.
Tables 5 and 6 present the mean total and
reducing sugars values, according to the type of drying,
pre-processing and storage time.
43
Effect of drying and storage conditions on the quality...
Coffee Science, Lavras, v. 2, n. 1, p. 38-47, jan./jun. 2007
Table 3 –
Mean electric conductivity values (
µ
Scm
-1
g
-1
) in storage conditions of 60% of relative humidity and temperature
of 23ºC, according to drying, pre-processing and storage time.
Means followed by the same letter, small in the lines for each storage time and capitalized in the columns for each type of pre-
processing, did not differ, at a 5%probability, through the Tukey test.
Table 4 –
Mean potassium leaching values (ppm/g), in storage conditions of 60% of relative humidity and temperature
of 23ºC, according to drying, pre-processing and storage time.
T
ime
(zero
days
) T
ime
(90 days
) T
ime
(180
days
)
Drying
processing
condition
Pre
-p
roc
ess
ing
Pre
-p
rocess
ing
Pre
-p
rocess
ing
Natural
Washed
Natural
Washed
Natural
Washed
Yard
26,6 A a
23,3 A a
37,2 B b
22,5 A a
43,2 B b
33,7 A a
40ºC
40,0 B b
35,0 B a
27,4 A a
28,4 B a
38,1 A a
40,2 B a
60ºC
66,3 C a
68,3 C a
72,22 C a
75,3 C a
75,0 C a
75,7 C a
Means followed by the same letter, small in the lines for each storage time and capitalized in the columns for each type of pre-
processing, did not differ, at a 5%probability, through the Tukey test.
Table 5 –
Mean reducing sugars values (%), in storage conditions of 60% of relative humidity and temperature of 23ºC,
according to drying, pre-processing and storage time.
Time (zero days)
Time (90 days)
Time (180 days)
Drying
processing
condition
Pre
-
processing
Pre
-
processing
Pre
-
processing
Natural
Washed
Natural
Washed
Natural
Washed
Yard
0,85 C b
0,47 C a
0,75 C b
0,37 C a
0,64 C b
0,38 B a
40ºC
0,64 B b
0,35 B a
0,62 B b
0,32 B a
0,58 B b
0,25 A a
60ºC
0,57 A b
0,27 A a
0,47 A b
0,19 A a
0,45 A b
0,22 A a
Means followed by the same letter, small in the lines for each storage time and capitalized in the columns for each type of pre-
processing, did not differ, at a 5%probability, through the Tukey test.
Table 5 shows that the reducing sugars values
decreased as drying temperature and storage time
increased, independent of the type of processing.
Table 6 presents a reduction of the total sugars
as drying temperature increased. The lowest values,
when compared to the type of processing, were found
in the washed coffee. The natural coffee presented
approximately twice the amount of total and reducing
sugars in relation to the washed coffee. This is due
to the fact that a large part of the sugars in coffee
are located in the husk and mucilage (
LOPEZ
et al.,
2000).
The low reducing sugars content in the coffee
beans is associated to the low electric conductivity
and potassium leaching values observed in Tables 3
and 4, probably due to the drying temperature.
Afonso Júnior (2001) observed a decrease in
the reducing sugars content as storage time increased,
Time (0 days)
Time (90 days)
Time (180 days)
Drying
processing
condition
Pre
-
processing
Pre
-
processing
Pre
-
processing
Natural
Washed
Natural
Washed
Natural
Washed³
Yard²
114,0 A b
85,6 A a
115,2 A a
109,2 A a
143,6 A a
142,1
B a
40ºC
130,0 B b
93,3 A a
126,6 B b
110,6 A a
146,8 A b
128,0 A a
60ºC
230,0 C b
215,0 B a
235,1 C b
215,1 B a
240,0 B b
225,8 C a
CORADI, P. C. et al.
44
Coffee Science, Lavras, v. 2, n. 1, p. 38-47, jan./jun. 2007
Table 6 – Mean total sugars values (%), in storage
conditions of 60% of relative humidity and temperature of
23ºC, according to drying, pre-processing and storage
time.
Pre
-
processing
Drying processing
condition
Natural
Washed
Yard
40ºC
7,64 B b
7,88 B a
6,96 B a
7,54 C a
60ºC
7,23 A b
6,44 A a
Means followed by the same letter, small in the lines for each
storage time and capitalized in the columns for each type of
pre-processing, did not differ, at a 5%probability, through the
Tukey test
concluding that any probable effects would be due to
the greater metabolic activity in the beans during
storage.
The low reducing sugars content is related to
the loss of quality in the coffee beans. However, to
better understand the relation between reducing
sugars and the effects of drying and pre-processing
during storage, it would be necessary to study
separately the glucose, frutose, arabinose, manose,
galactose, ribose and ramose quantities, as they
contribute to the formation of the reducing sugars in
the product.
The variations of the mean total titrable acidity
values, in the different types of drying and storage,
are presented in Table 7.
According to the data presented in Table 7,
the highest total titrable acidity values were observed
in drying at 60ºC. During storage, these values tended
to be more similar independent of the drying process.
The higher total titrable acidity values observed in
Table 7 –
Mean total titrable acidity values (NaOH 0,1N/100g), in storage conditions of 60% of relative humidity and
temperature of 23ºC, according to drying and storage time.
Storage Time
Drying processing
condition
Zero
90 d
ays
180 d
ays
Yard
177,50 A a
216,67 B b
207,50 A b
40ºC
175,50 A a
191,67 A b
198,33 A b
60ºC
212,50 B a
212,50 B a
210,00 A a
Means followed by the same letter, small in the lines for each type of drying and capitalized in the columns for each storage time
did not differ, at a 5%probability, through the Tukey test.
drying at 60ºC are due to the fermenting processes
that occur in the husk and the pulp (
LEITE
et al.,
1998).
Acidity is one of the characteristic attributes
of coffee sensorial analysis. Its intensity varies,
predominantly, according to the stage of maturation
of the beans, pre-processing and drying. Storage,
however, also influences coffee acidity (
COELHO
et al., 2001). These values may be linked to the
increase of potassium leaching and electric
conductivity, both of which demonstrated a
degeneration of the cellular membranes. In this work,
storage led to greater acidity, in other words, the effect
of drying was minimized throughout storage time.
Table 8 presents the fatty acidity results,
according to drying, pre-processing and storage, during
180 days at 60% relative humidity and 23ºC
temperature conditions.
Table 8 shows that the fatty acidity values
increased with an increase of the drying temperature
and of storage time.
Higher drying temperatures in longer storage
periods, with relative humidity at 60%, may be related
to the degeneration of the cellular membranes and,
consequently, to the leaking of the oils that participate
in the chemical composition of the beans. These oils
can oxidize the structure of the coffee beans, affecting
the quality of the product (
AFONSO JÚNIOR
, 2001).
Esteves (1960) observed that, as the storage time
increases, the oils become more acid and the quality
of the product becomes poorer.
The pre-processing of the coffee also
influenced the fatty acidity values. Table 8 shows that
at the beginning of storage the natural coffee
presented higher acidity values when compared to
the washed coffee. This process could be due to the
degradation of the coffee, caused by the high drying
45
Effect of drying and storage conditions on the quality...
Coffee Science, Lavras, v. 2, n. 1, p. 38-47, jan./jun. 2007
Table 8 –
Mean fatty acidity values (KOH 0,1N/100g), in storage conditions of 60% of relative humidity and temperature
of 23ºC, according to drying and storage time.
Natural
Washed
Drying processing
condition
Time
Time
Zero
90 d
ays
180 d
ays
Zero
90 d
ays
180 d
ays
Yard
0,77 A a
1,49 A b
2,70 A c
0,77 A a
1,29 A b
3,44 A c
40ºC
1,27 B a
1,85 B b
5,51 B c
1,08 A a
1,30 A a
5,22 B b
60ºC
2,63 C a
3,55 C b
5,74 B c
1,54 B a
2,30 B b
5,78 B c
Means followed by the same letter, small in the lines for each type of processing and capitalized in the columns for each storage
time did not differ, at a 5%probability, through the Tukey test.
temperature, which could be damaging the structure
of the cellular membranes and leaking the constituting
oils. These oils would enter a process of permanent
oxidizing.
However, with the longer storage period,
the effects of pre-processing are balanced and
deterioration is caused, generally, by the
combination between 60% of relative humidity and
storage temperature of 23ºC, independent of
drying.
The mean sensorial analysis values, according
to drying, pre-processing and storage, are presented
in Table 9.
Table 9 shows that, in general, sensorial
analysis had the greatest effects, according to drying
temperature and pre-processing. The increase of
Table 9 –
Mean sensorial analysis scores, in storage conditions of 60% of relative humidity and temperature of 23ºC,
according to drying, pre-processing and storage time.
Time (zero)
Time (90 days)
Ti
me (180 days)
Drying
processing
condition
Pre
-
processing
Pre
-
processing
Pre
-
processing
Natural
Washed
Natural
Washed
Natural
Washed
Yard
74,3 B a
80,8 A b
73,3 B a
80,3 A b
74,1 B a
80,8 B b
40ºC
72,2 A B a
81,3 A b
73,5 B a
80,2 A b
73,4 B a
77,4 A b
60ºC
68,1 A a
79,6
A b
70,8 A a
81,0 A b
70,8 A a
78,0 A b
Means followed by the same letter, small in the lines for each storage time and capitalized in the columns for each type of pre-
processing, did not differ, at a 5%probability, through the Tukey test.
drying temperature in natural coffee led to the lowest
sensorial attributes scores while, in the washed coffee,
the increase of temperature had no significant
influence over the values obtained. The drying on a
yard had the best scores, independent of the type of
pre-processing. Storage time, in the conditions studied,
did not alter the sensorial characteristics of the
product.
The washed coffee presented the best scores
(Table 9) in all the storage periods, when compared
to the natural coffee, independent of the types of
drying.
These sensorial analysis results are consistent
with the electric conductivity, potassium leaching, total
titrable acidity, fatty acidity and total and reducing
sugars results discussed above.
CORADI, P. C. et al.
46
Coffee Science, Lavras, v. 2, n. 1, p. 38-47, jan./jun. 2007
4 CONCLUSIONS
The coffee dried at 60ºC and stored for 180
days presented the worst electric conductivity,
potassium leaching and fatty acidity results.
The total and reducing sugars content was
greater for the coffee dried on a yard during the first
90 days of storage.
After 90 days of storage, the total titrable acidity
values increased as drying temperature was elevated.
The sensorial analysis values of natural coffee
were negatively affected by the increase of drying
temperature.
The physical-chemical analyses in the drying
and storage conditions studied showed that washed
coffee presented the highest quality in comparison to
the natural product.
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