Extraction of Coconut Milk by Continuous

Screw Press 1
L. E. Cancel, J. A. Rosario-Hernández, and E. R. de Hernández2
INTRODUCTION
One of the most important operations in the extraction of coconut milk
is the pressing of the comminuted pulp. A rack and cloth hydraulic press (3)
is used presently for this. A roller mill press (5) and a combination of cen-
trifuge and rack cloth press (4,6) also have been used.
The rack and cloth hydraulic press system has been used extensively in
industry in Puerto Rico for this purpose. The operation has been studied
thoroughly and found to be efficient. It has the disadvantage of being a
batch-type operation, however, requiring at least two operators to make it
practical. The main objections to the batch process are the difficulties in
standardizing it and its high operating costs. The rack and cloth hydraulic
press system also presents sanitation and quality problems. As cloth is used
to hold the comminuted pulp, the cleaning and maintenance of this material
adds to the cost of production. The use of the required racks also creates a
cleaning problem. Due to their construction design, this accessory has to be
sanitized thoroughly or the flavor of thefinishedproduct will be impaired.
In an effort to solve the problems present in the rack and cloth hydraulic
processing operation, studies were conducted to adapt one of the new ma-
chines now available to the coconut milk extraction process on the market.
A screw press designed primarily for the extraction of grape juice was used
in this work. The results of the study are presented herewith.
MATERIALS AND METHODS
The coconuts used in the experiments were purchased at the fresh-pro-
duce market. They were husked and the nuts sorted before processing.
Nuts were discarded which were soft in the eye at the embryo end, cracked
or immature. Selected nuts were heated to 307° F (60 lbs steam pressure)
for 8 min in a high-pressure vessel (1). The retort was equipped for a fast
coming-up and an instant release of pressure during the operation. Immedi-
ately after the heat treatment the coconuts were broken in a coconut break-
ing machine (2). The broken nuts were carried by a conveyor to a sorting
table where the pulp was separated and fed into a washing reel. The clean
1
Manuscript submitted to Editorial Board December 10,1973.
2
Food Scientist and Research Assistants, respectively, Food Technology Labora-
tory, Agricultural Experiment Station, Mayagiiez Campus, University of Puerto
Rico, Río Piedras, P.R.
322
 CONTINUOUS EXTRACTION OP COCONUT MILK BY SCREW PRESS 323

pulp was weighed and ground in a hammer mill equipped with a No. 4
screen (10 H-inch perforations/in2). One part by weight of water was added
to every two parts of pulp in the comminuting mill.
The comminuted pulp was weighed before feeding into the screw-press.
An initial amount of 30 lbs of comminuted pulp was fed into the press to
fill the machine and leave it in actual pressing condition. One hundred lbs
of pulp were used per run. Material was added to the press in such a way
as to just fill the inlet space of the machine cylinder. Bridging was avoided
by making sure not to over fill this space. Time was recorded during the
feeding operation, and an additional 2 min were allowed to empty the
press. This timing procedure was followed for all the experiments in order
to duplicate pressing conditions. A record of the weight of the mash, the
time needed to feed the machine, the weight of the coconut milk and that of
the screw-press cake (pressed residue) was kept for each run. Samples of
the coconut milk and press cake were taken and weighed for chemical
analyses.
Fourteen lbs of solid residue from the screw press were squeezed in the
hydraulic press to evaluate the continuous press operation. This evaluation
was carried out by pressing the solid residue under a pressure of 185 lbs/in2
and holding it for 1 min. The weights of the coconut milk and of the solid
residue left were recorded. The practical efficiency of the operation was
calculated from the results obtained. These pressing conditions were used
for the evaluation, as they are the optimum ones for maximum extraction
of coconut milk.
The screw press used was a Bietz Horizontal Continuous S-Press Model
No. 63 equipped with a variable speed drive at the main screw shaft to con-
trol the capacity of the press and with a 0.023-in perforation screen. In this
machine the speed of the creeping cone (discharge end valve of the cylinder)
was 3 r/min. The pressure needed to operate the creeping cone was provided
by a high pressure nitrogen tank connected to the hydraulic piston of the
accessory. Working pressure on the discharge end valve was regulated
through a pressure regulator on the machine and another placed in the tank.
With the use of the nitrogen tank no fluctuations were observed in the
system during the operation. This made it possible to make precise adjust-
ments of pressure ranging from 60 tp 200 lbf/in2.
As all the previous experiences in the extraction of coconut milk sug-
gested pressures close to 180 lbf/in2 (1), the work was started with variations
ranging from 160 to 200 lbf/in2. The results of the experiments revealed no
8
Trade names are used in this publication for the sole purpose of providing specific
information. Mention of a trade name does not constitute a guarantee or warranty of
the equipment by the Agricultural Experiment Station of the University of Puerto
Rico or an endorsement over other equipment not mentioned.
324 JOUENAL OF AGRICULTURE OP UNIVERSITY OP PUERTO RICO

definite trends in capacity, efficiency and yield of operation at these high

pressures. On the other hand, detrimental effects were observed with these
working pressures in the machine, such as an excessive leakage through the
retainer in the creeping cone. Besides, the coconut rrrilk produced contained
an excess of coconut pulp particles. For these reasons high pressures were
discarded.
An initial experimental survey of the effect of pressure in the extraction
of coconut milk, starting with a level as low as 20 lbf/in2, led to the estab-
lishment of pressure limits for the study. Because in this preliminary study
pressures under 50 lbf/in2 resulted in cake with a high coconut milk content,
it was decided to set the pressures between 60 and 180 lbf/in2 and the speed
from 8.5 to 17.5 r/min.
The evaluation of the performance of the continuous screw press will be
presented by using six indices: capacity, efficiency, and extraction yield of
the machine, and percent of coconut milk, water, and fat (dry basis) re-
maining in the press cake.

RESULTS AND DISCUSSION

•
The capacity of the screw press is shown in the curves obtained by plot-
ting the results of the experiments performed (fig. 1). With speeds of 8.5
and 12.5 r/min, the pressure does not seem to influence, in a fixed pattern,
the amount of coconut pressed per hour. At these two speeds, the capacity
remains almost constant, with irregular fluctuations that can be explained
by the inconsistency of the operator in feeding the machine. The screw
press has an increase in capacity of about 30 percent when the speed is
raised from 8.5 to 12.5 r/min. The results show that at a speed of 17.5 r/min
a reducing effect occurs in the capacity of the machine as the pressure is
increased from 60 to 180 lbf/in2. The pressure at the discharge valve is great
enough to reduce the release of solid material. This also is corroborated by
the coconut milk obtained at higher pressures which contains more pulp
particles forced through the screen by the excessive pressure inside.
Raising the speed of the press from 8.5 to 17.5 r/min at 100 lbf/in2, there
is an increase in capacity of 125 percent, reaching a level of 3,000 lbs of
comminuted pulp/hr.
Another index to evaluate the performance of the screw press is its effi-
ciency as compared to the batch hydraulic press, taking the latter as 100
percent efficient.
Percent efficiency = weight of coconut milk from screw press/weight of coconut milk
from screw press + weight of coconut milk obtained from residue of
screw press when placed in hydraulic press X 100
 CONTINUOUS EXTRACTION OF COCONUT MILK BY SCREW PRESS 32£

40 r-

OS
D
O 30 -
s 17.5 r . p . m .
tí,
w
Pi
W
M
J
o
o

cu
(4
Oí
5 20 12.5 r . p . m .
w

H
u
< 8. 5 r . p . m .
o

10 J. i _L l J_ J_ _l_
^0 80 100 120 140 160 180
PRESSURE ON CREEPING CONE • PSI
Fio. 1.—Amount of comminuted coconut pulp pressed at seven different pressures
on the creeping cone and three different speeds.

The curves presented in figure 2 (top) were obtained by plotting the

figures calculated from the results. Irrespective of the pressure, the data
show that the highest efficiency is obtained with a speed of 8.5 r/min fol-
lowed by a speed of 12.5 and finally 17.5 r/min. As the pressure is increased,
the efficiency seems to reach a common level, disregarding the difference in
r/min of the cone. It is important to notice that the difference in efficiency
is only 2.5 percent at most (60 lbf/in2) going down to 0.6 percent at 180
lbf/in2.
The percent yield index, the amount expressed in pounds of coconut milk
extracted from 100 lbs of comminuted pulp (fig. 2, middle curves), shows
that the performance of the screw press varies inversely with the increase in
326 JOURNAL OF AGRICULTURE OP UNIVERSITY OF PUERTO RICO

100 r-

Efficiency in operation

90

80

70

60 U
17.5 r . p . m .
---12.5 r.p.m.
8.5 r.p.m.

40

H
2 Milk in acrew-prea» cake
W
O
«
W 30
0.

20

10 _i_
60
a.
80 100
x 120 140 160 180
PRESSURE ON CREEPING CONE - PSI

FIG. 2.—Performance of the screw-press in extracting coconut milk at seven differ- *

ent pressures on the creeping cone and three different speeds.

speed. The yield is highest at the lower speed of 8.5 r/min, followed by 12.5
r/min and 17.5 r/min. The results of the experiments show a yield differ-
ence of about 6 percent for 60 lbf/in2, going down to 2.5 percent at 180
lbf/in2.
The results of the coconut milk extraction in the screw-press cake (fig. 2
bottom curves) show that the most complete extraction is obtained at 8.5
r/min, followed by 12.5 and 17.5. These results agree with those given by
the percent yield curve.
The results of the water and fat analysis in the screw-press cake are
presented in figure 3. Water content in press-cake from extractions at 8.5
 CONTINUOUS EXTRACTION OP COCONUT MILK BY SCREW PRESS 327

and 12.5 r/min are within 1 percent, but the results for 17.5 r/min differ
from the latter by 3.5 to 4.0 percent. Fat analyses of the screw-press cake
show a definite difference in fat content between the three pressing condi-
tions, but these differences are not related to speed.
In a practical evaluation using the calculated indices obtained from the
results of the study carried out, it was concluded that the best conditions
to operate the screw press for the extraction of coconut milk are a speed of
17.5 r/min and a pressure of 100 lbf/in2 in the creeping cone (solids release
valve). The efficiency index shows that the performance of the screw press
is 90 to 95 percent as efficient as that of the hydraulic press but it reduces

60 - WATER CONTENT

50

40

30 17.5 r . p . m .
- - - - 12. 5 r . p . m .
____ 8.5 r . p . m .
Z
w
u
w
ft
60 - FAT CONTENT (DRY BASIS)

50

40

30
60 80 100 12 120 140 160 180
PRESSURE ON CREEPING CONE - PSI

FIG. 3.—Chemical analysis of screw-press cake obtained from experiments at seven

different pressures and three different speeds.
328 JOURNAL OP AGRICULTURE OP UNIVERSITY OP PUERTO RICO

operating costs and permits continuity in the coconut milk extraction. The
yield values show that the difference between coconut milk extraction at
different speeds (5 to 7 %) is not comparable to the difference in capacity
at the speeds used (125 percent increase). Chemical analyses of the coconut
milk and press cake reveal no trend in the fat content of either product with
respect to the treatments given.
SUMMARY
Studies were conducted on the extraction of coconut milk using a con-
tinuous screw press. Speeds of 8.5, 12.5, and 17.5 r/min were used on the
pressing screw. Pressures of 60, 80, 100, 120, 140, 160 and 180 lbf/in2 were
used on the creeping cone, which in this machine serves as a solids releasing
valve. A hydraulic press was used to evaluate the screw-press cake by com-
pletely removing the remaining coconut milk from the pressed solid material
under a direct pressure of 185 p.s.i./m2 for 1 minute.
The results of the experiments indicate a gradual increase in efficiency in
the coconut milk extraction process as the pressure is .augmented from 60
to 180 lbf/in2, with a more pronounced effect within the range of 60 to 100
lbf/in2. The increase in efficiency ranged from 3.5 percent at 8.5 r/min to
6.5 percent at 7.5 r/min.
Capacity in the performance of the press is the characteristic most af-
fected by changes in speed of the pressing screw. The capacity at a speed of
17.5 r/min dropped from 3,160 to 2,720 lbs/hr. With a speed of 12.5 r/min
the capacity fluctuated between 1,800 and 1,700 lbs/hr, and at 8.5 r/min
it was about 1,300 lbs/hr.
The recommended set of conditions to extract coconut milk using this
type of continuous screw-press are a speed of 17.5 r/min and a pressure of
100 lbs on the creeping cone, when working with comminute material from
a hammer mill with a No. 4 screen (10 34-in perforations/in2).
RESUMEN
Se estudió el procedimiento para extraer leche de coco usando una prensa de tornillo
de operación continua, a velocidades de 8.5,12.5 y 17.5 r.p.m. en el tornillo alimenta-
dor y presiones de 60, 80,100,120,140,160 y 180 p.s.i. en el cono-válvula a la salida
de la prensa. En la evaluación de la operación de la prensa de tornillo se usó una prensa
hidráulica, calibrada para trabajar a una presión de 185 p.s.i./m8 for 1 minute.
El residuo sólido de la prensa de tornillo se sometió a la acción de la prensa hidráu-
lica para extraer la leche de coco residual. Los resultados de los experimentos indican
un aumento gradual en la eficiencia del proceso de extracción de leche de coco, según
se aumenta la presión en el cono-válvula de 60 a 180 lbs./pulg.2, notándose, sin em-
bargo, un cambio más pronunciado entre 60 y 100 lbs. de presión. El aumento en la
eficiencia a una velocidad de 17.5 r.p.m. fluctúa entre 3.5 y 6.5 por ciento.
En el funcionamiento de la prensa de tornillo, es la capacidad la característica que
más se afecta con los cambios en la velocidad del tornillo alimentador. Esta varía de
 CONTINUOUS EXTRACTION OP COCONUT MILK BY SCREW PRESS 329

2,720 a 3,160 lbs. por hora a una velocidad de 17.5 r.p.m.; de 1,700 a 1,800 lbs. a 12.5
r.p.m.; y fluctúa alrededor de 1,800 lbs. a una velocidad de 8.5 r.p.m.
Como resultado del estudio efectuado se recomiendan las siguientes condiciones
para el funcionamiento de la prensa de tornillo en la extracción de leche de coco: una
velocidad de 17.5 r.p.m. en el tornillo sinfín; 100 libras de presión por pulgada cua-
drada en el cono-válvula; y la molienda de la pulpa de coco en un molino de martillos
equipado con un cedazo Núm. 4 (10 perforaciones de 0.25 pulgada/pulg.2 de diámetro
de superficie).
LITERATURE CITED
1. Cancel, L. E., Method of shelling coconuts, U.S. Patent 3,225,804,1965.
2. , Coconut breaking machine, U.S. Patent 3,695,834,1969.
3. , Coconut food products and bases, Chapter 9, Coconuts: Production-Process-
ing-Products, edited by J. G. Woodroof, Avi Publishing Co., Westport, Conn
162-88,1970.
4. Hagenmaier, R., Cater, C. M., and Mattil, K. F., Critical unit operations of the
aqueous processing of fresh coconuts, J. Am. Oil Chem. Soc. 49 (3): 178-81,1965.
5. Lava, V. G., Oil recovery, U.S. Patent 2,101,371,1937.
6. Raxas, P. G., Process of recovering oils from oleoginous meats of nuts, beans and
seeds, U.S. Patent 3,083,365,1963.