Journal of Food Engineering 26 (1995) 431-442

Copyright 0 1995 Elsevier Science Limited

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ELSEVIER

Abrasive Peeling of Potatoes

K. K. Singh* & B. D. Shukla
Central Institute of Agricultural Engineering, Nabibagh, Berasia Road, Bhopal
(M.P.) 462038, India
(Received 19 November 1992; revised version received 13 June 1994;
accepted 3 October 1994)

ABSTRACT
For the processing of potatoes in any form, removal of peel is an
important unit operation. Hence, a power operated batch type potato
peeler was developed and its pegormance
was evaluated. The main
parts of the machine are a peeling drum and a water spraying unit. The
peeling drum with protrusions on the inside surface rotates and
detaches peel from potatoes by abrasion. The water spraying unit
washes the potatoes and simultaneously peel is removed from the drum
through the perforation along with the flow of water: The capacity of
the machine is 100 kglh with a peeling ejjiciency and peel losses of
78% and 6%, respectively. The machine costs around Rs 6500.00
($250) along with an electric motor and is suitable for a small scale
processor of potato chips and other products. The estimated cost of
peeling of 1 ton potatoes is only Rs 100.00 ($3.85).

NOTATION

Equivalent

diameter (mm)
and thickness, respectively
Peeling efficiency (%)
Power requirement (W)
Batch load of potatoes (kg)
Correlation coefficient
Peeling time (min)

L, B, T Length, breadth

r
t

of the tuber (mm)

*Present address: PHTC, Agricultural and Food Engineering Department,

Institute of Technology, Kharagpur 721302, India.
431

India

432

K. K. Singh, B. D. Shukla

Peel losses (%)

Spheric@
INTRODUCTION

The total annual production of potatoes in India is about 15 million tons

and a substantial amount of it is lost at various stages of post harvest
operations,
mainly due to inadequate
storage facilities (Subrahmanyam,
1986). Hence, appropriate
processing
technology
and equipment
are
essential to produce potato food products on a small scale. It will help to
reduce the losses and generate income and employment
in the rural or
semi-urban areas.
Removal of peel is one of the important unit operations for the further
processing of potatoes in any form. The potato chip is a very popular snack
food in India. For making chips, the important preparatory operations are
washing and peeling. Hand peeling is traditional in India and is tedious and
time consuming. Moreover, the loss of flesh is very high. However, the
potato processing industry uses lye peeling. Since, in lye peeling process, the
heat ring is formed below the surface of the potato due to tissue damage
and polyphenol enzyme activity, it is not recommended for making the chips
(Huxsoll& Smith, 1975). For this purpose, abrasive type potato peelers have
been recommended
(Campbell,
1982). Pollak and Ignall (1959) also
reported the comparative evaluation of various types of small, portable and
electrically operated batch type abrasive peelers.
Keeping the above facts in view, a batch type power operated abrasive
potato peeler was developed and evaluated. The important features of the
peeler are reported in this paper.

MATERIALS

AND METHODS

The abrasive potato peeler

The constructional drawings of the peeler are shown in Figs 1, 2 and 3. The
main part of the peeler is an abrasive drum, 670 mm length and 450 mm
diameter, made of stainless steel sheet. The inside surface of the drum has
protrusions (2.5-3.0 mm). To develop the protrusions, the stainless steel
sheet was bent into a cylindrical shape and it was punched from one side
with a die at a fixed spacing. It was then filed to flatten the sharp points
developed from punching to ensure smoother peeling of the potatoes.
The centre to centre spacing between rows and columns of protrusions
are 14 and 7 mm, respectively. The drum is fixed on a horizontal shaft
supported by two ball bearings (30 mm ID) fixed over a frame of size
1080 x 700 x 1150 mm. For loading and unloading the unpeeled and peeled
potatoes, respectively, an inlet and outlet have been provided. The abrasive
peeling takes place due to the movement of the potatoes inside the rotating
drum. The drum is rotated by means of belts and pulleys connected to a 1.5
h.p. single phase electric motor. A water spraying unit of galvanized iron
(GI) pipe of 15 mm diameter having 8 nozzles is provided to remove peels

Abrasive peeling

of potatoes

433

P-

Fig. 1.

Front view of potato peeler: (1) electric motor; (2) driven shaft; (3) V-belt;
(4) waste water and peel collection tray; (5) bolts and nuts; (6) washing system
assembly; (7) peeling drum shaft assembly; (8) V-pulleys; (9) bearing block. (All
dimensions in mm.)
from the drum and simultaneously
wash the peeled potatoes. A water
collection trough to drain out the water and peels has also been provided
beneath the drum.
EXPERIMENTAL

PROCEDURE

The Kufri-Jyoti variety of potatoes (Solanum tuberosum L.) about 4 months

old were used for the experiment. The experiment was conducted during the

434

K. K. Singh, B. D. Shuklu

Side view of potato peeler: (1) frame assembly; (2) foundation of motor;
(3) inlet and outlet cover; (4) on-off valve; (5) water supply connection pipe. (All
dimensions in mm.)

Fig. 2.

year 1991-2. The length, breadth and thickness of potatoes were measured
using a Vernier calliper. The following formulae were used to calculate the
equivalent diameter D,, and sphericity C#J
of the potatoes (Mohsenin, 1970):
D,,=(LBT)*3
where L is the length, B is the breadth and T is the thickness, and

435

Abrasive peeling of potatoes

Details
Fig. 3.

of Abrasion

Details of abrasive drum used in potato peeler (all dimensions

in mm).

For determination
of the peel content, five samples of 200 g each were
weighed separately and recorded.
The potato samples were boiled in water for 05 h to loosen the peels.
After cooling the boiled potatoes at room temperature (30-32C) for about
05 h, the peels were separated from the flesh manually. The peels and
potatoes were then dried in an air oven at 80C for about 6 h. The peel
percentage was then calculated by using following formulae:
Peel content

(% db)=

Dried wt of peel
Dried wt of potato sample

x 100

The machine was set for the experiment. A sample of five potatoes was
weighed individually and marked for identification.
For marking, the
potatoes were punched with a pin and different colour dyes were poured on
each sample. These marked potatoes were then mixed with the experimental
batch load in the drum. For experimental purposes, a known quantity (5, 10,
15 and 20 kg) of potatoes was fed into the drum. The inlet pipe of the water
spraying unit was connected to a water tap. The drum was then rotated at
speeds of 30 and 40 rev/min.
The speed was varied by changing the pulley of the drum shaft. The
marked samples were taken out for analysis after 4, 6, 8 and 10 min. The
samples were gently wiped with blotting paper to remove the surface
moisture and weighed immediately. The peel content of these potatoes was
determined
with the help of the above mentioned
formula. The water
drained was collected and weighed to determine the quantity of water
required to perform the operation.

K. K. Singh, B. D. Shukla

436

Each experiment was carried

reported.
Peeling efficiency (s) =

out in triplicate

Fraction of remaining
on peeled potato

and average

values

are

1x

100

Fraction

of peel on raw material

The percentage peel losses were determined

(Willard, 1971):
Peel losses (a)=

by using the following formula

Weight of raw potatoes-Weight

of peeled potatoes

x 100

Weight of raw potatoes

RESULTS

AND DISCUSSION

The mean equivalent diameter of the potatoes used for the experiments was
found to be 62 mm with a standard deviation of k4 mm. The mean
sphericity and peel content were determined as 0.65 and 1+38%, respectively.
Figures 4 and 5 show the relationship between time and peeling efficiency
at different batch loads from 5 to 20 kg for drum speeds of 30 and 40 rev/
min, respectively.

Drum

speed:

30rpm

6
Time,t

Fig. 4.

(h)

Relationship between time and peeling efficiency at different batch loads

(*, 5 kg; A, 10 kg; II, 1.5 kg; o, 20 kg).

437

Abrasive peeling of potatoes

Drum

20 1

speed :COr pm

I
L

10

12

Time,t

Fig. 5.

Relationship

(h)

between time and peeling efficiency at different

(*, 5 kg; A, 10 kg; q, 15 kg; o, 20 kg).

batch loads

Regression on the data leads to the following equations for batch loads of
5, 10, 15 and 20 kg and speeds of 30 and 40 rev/min, respectively.
At 30 rev/min drum speed:
v]= - 35.28 + 20.48t - 0*72t2

(r*=0*98)

(1)

v]= -12*32+

(r-*=0*99)

(2)

(r2=0*99)

(3)

(r2=0.98)

(4)

Y/= -29*77+20*93t-0*81t2

(r*=0*99)

(5)

ij= -26_66+22*15t-0*95t2

(r*=0*99)

(6)

(r2=0*89)

(7)

(r*=0.98)

(8)

16*61t-0*59t*

~j=11~78+10~32t-O~21t*
rj=18*72+8*65t-0*19t2
At 40 rev/min drum speed:

r/=31*95 + 1.56t-0*53t*
~=13~36+10~11t-0~23t2

It is clear from Figs 4 and 5 that peeling efficiency

increases with time. At

higher times, potatoes get more chances to remain in contact with the
abrasive surface and thereby more peel is removed from its outer surface,
thus the peeling efficiency increases.
It is also observed that initially the peeling efficiency increases with
increasing batch load, but this trend is not continued beyond 6 min (Table
1). This may be due to the fact that at the initial stage of peeling only the
outer surface of the potatoes is removed but if the peeling continues beyond
6 min at the higher batch load, some potatoes are overpeeled whereas some
are underpeeled which affected the trend of the result.

438

K. K. Singh, B. D. Shukla

The peeling efficiency increases with an increase in drum speed (30-40

rpm). At higher speeds, potatoes come more frequently in contact with the
abrasive surface of the drum, and hence more peel is removed, increasing
the peeling efficiency.
Figures 6 and 7 show the effect of peeling time on peel losses at different
batch loads from 5 to 20 kg for drum speeds of 30 and 40 rev/min,
respectively.
Regression analysis on the data leads to the following equations for batch
loads of 5, 10, 15 and 20 kg and speeds of 30 and 40 rev/min, respectively.
At 30 rev/min drum speed:
&=0*37 + 0*54t

(r2= 1)

(9)

a=O*83 + 0.54t

(r2= 1)

(10)

&=1*30+0.54t

(r2= 1)

(II)

E= 1.76 + 0*54t

(r2= 1)

(12)

&=1*52+0*51t

(r2=0*97)

(13)

&=0*72+0*68t

(r2=0*97)

(14)

&=1*32+0*67t

(r2=0*99)

(15)

&=0*20 + 1*03t

(r2=0*98)

At 40 rev/min speed:

(16)
It is clear from Figs 6 and 7 that peel losses increase linearly with
increasing peeling time. This is due to the same reason as discussed in the
case of peeling efficiency. At higher peeling times the potatoes come in
contact with the abrasive surface for a longer duration which results in
removal of more peel and flesh, hence peel losses increase.
It is also observed that peel losses increase at higher loading density. It
may be that too small a load allows the potatoes to bounce and skip over
the abrasive surfaces resulting in incomplete peeling (Huxsoll & Smith,
1975). Besides, at higher loading density, the removal of peel and flesh were
higher in quantity which increased peel losses.
The peel losses were observed to be higher at 40 rev/min than 30 rev/min
speed. This may be due to the same reason as discussed for peeling
efficiency.
Figure 8 shows the effect of batch load on power requirement
at drum
speeds of 30 and 40 rev/min. These relationships are represented by eqns
(17) and (18). The relationship is found to be linear first order. It appears
that with an increase in batch load, the power requirement increases linearly
because at higher batch load, the friction between the abrasive surface and
the potatoes was higher and also the load over the drum was also higher
which increased the power requirement.
At 30 rev/min:
P=650 + 13Q

(r2=0*966)

(17)

(r2=O-966)

(18)

At 40 rev/min:
P=775 + 13Q

58.18
85.76
96.13
45.34
63.47
84.64
93.20
49.55
66.45
80.41
93.92
50.95
61.52
77.72
85.20

:
10
4

:
10
4
6
8
10
4

F?
10

10

20

15

36.24

40

62.74
82.29
90.23

70.58
91.30
99.46
49.85
51.35
87.97
98.04
51.07

65.39
87.69
98.10
47.26

4.68
6.23
7.56

4.24
4.98
5.95
3.55
4.10
5.58
6.42
4.24

3.56
4.68
6.23
3.10

2.51

30

Peel losses (%)

Speed (revlmin)

Peeling Times and Batch Loads

41.96

Speed (revlmin)

(min)

30

Peeling efficiency (%)

Peeling time

(kg)

TABLE 1
Values of Peeling Efficiency and Peel Losses at Different

Batch load

Experimental

5.37
8.85
10.37

5.09
5.76
7.74
3.97
5.45
6.67
8.05
4-46

4.36
5.42
6.85
3.41

3.80

40.

2
B
f?
5

2
%
$Y

K. K. Singh, B. D. Shukla

440

Orum

speed:

30rpm

Fig. 6.

Relationship

between
kg;

8
time,t

A,

Drum

10

(h)

time and peel losses at different

10 kg; q, 15 kg; o, 20 kg).

speed:

batch loads ( x , 5

4Orpm

0
P

6
Time

Fig. 7.

Relationship

between
kg;

A,

10

12

t (h)

time and peel losses at different

10 kg; q, 15 kg; o, 20 kg).

batch loads ( x , 5

441

Abrasive peeling of potatoes

sod5

10

Batch
Fig. 8.

Relationship

15

20

load, Q (kg)

between batch load and power requirement

(0, 30 rev/min; A, 40 rev/min).

Cost Economics

TABLE 2
of the Peeler for Peeling Potatoes

of the peeler

(1991-92)

Economic parameters

Value

Working capital (Rs (US$))

Annual fixed cost (Rs (US$))
Capital investment (Rs (US$))
Hourly variable cost (Rs (US$))
Annual variable cost (Rs (US$))
Total annual cost (Rs (US$))
Cost of operation (Rsih (US$/h))
Cost of processing (R&on (US%/ton))
Custom hiring charges (Rsiton (US$/ton))
Annual sales revenue (Rs (US$))
Annual net profits (Rs (US$))
Break-even-point,
in terms of
number of operations (h)
quantity handled (tons)
Pay-back period (years)
Return-on-investment
(%)
Employment generation per machine
(man-days/year)

169 (6.50)
2202 (84.70)
6551 (252.00)
5 (0.19)
8000 (307.69)
10202 (392.38)
6.37 (0.245)
100 (3.85)
200 (7.69)
20480 (787.69)
10278 (395.30)

1 US$=26

282
22.60
0.603
156.89
305

Indian rupees (Rs).

A speed of 30 rev/min batch load of 20 kg and time of 8 min were found

to be the best combination because of higher peeling efficiency and lower
peel losses. With this combination of parameters, the peeling efficiency and
peel losses were 78% and 6%, respectively. If the time of loading and
unloading the potatoes manually was 4 min and the actual peeling time was
8 min, the capacity of the machine was found to be 100 kg/h. The total

442

K. K. Singh, B. D. Shukla

quantity of water required to drain the peels and wash the potatoes was
found to be 1.25 litres/kg of potatoes.
The cost of fabrication of the peeler was estimated at Rs 6500.00 (US
$250). An economic
analysis was calculated
for peeling potatoes
by
comparing the machine costs to that of traditional hand peeling. Working
capital investment, cost of operation per hour and cost of peeling per kg of
potatoes,
break-even
point, pay-back period, return-on-investment
and
employment generation were estimated using standard procedures in order
to determine
the economic viability of the equipment
(Table 2). This
includes the cost of peeler, rent (Rs 25.00 per month), custom rate (Rs 0.20
per kg), hours of use per year (1600), labour charges (Rs 24 per day), useful
life (10 years), depreciation
(10% cost of the machine), interest (15%
annual of machine cost) and repair and maintenance charges (5% annual of
machine cost). These costs were estimated based on the price structure of
the year 1991-92.

REFERENCES
Campbell, J. K. (1982). Machinery for village level processing of potatoes. American
Society of Agricultural Engineers, Technical Paper No: 82-6513, pp. 1-19.
Huxsoll, C. C. & Smith, T. (1975). Peeling potatoes for processing. In Potatoes
Processing, eds W. F. Talburt & 0. Smith. AVI Publishing Co., Westport, CN, pp.
275-304.
Mohsenin, N. N. (1970). Physical Properties of Plants and Animal Materials. Gordon
and Breach Science, New York.
Pollak, G. A. & Ignall, H. R. (1959). Comparative evaluation of various small
capacity commercial potato peelers. Food Technol., 13, 276-80.
Subrahmanyam, K. V. (1986). Post harvest losses in horticultural crops: an appraisal.
Agric. Situation in India, 41 (5), 339-43.

Willard, M. J. (1971). A grading system of peeled potatoes.

Util. Conf., July 28.

Proc. 2Zst Nat. Potato