BA
TECHNOLOGY
TRANSFER
DR/
O\USFIC
PEELING
OF
CLINGSTONE
PEACHES
US.
ENVIRONMENTAL
PROTECTION
AGENCY
INDUSTRIAL
DEMONSTRATION
GRANT
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EFA
TECHNOLOGY
TRANSFER
DRY
CAUSTIC
PEELING
OF
CLINGSTONE
PEACHES
US.
ENVIRONMENTAL
PROTECTION
AGENCY
INDUSTRIAL
DEMONSTRATION
GRANT
-------
The annual production
of canned clingstone
peaches in the United
States exceeds 30 million
cases. These peaches are
canned during a season
ranging from a few weeks
to a maximum of three
months. Since the wastes
from canning operations
are produced over such
short time periods, they
present problems in
economic design
utilization and operation
of treatment plants.
Peeling is the largest
single source of waste
from fruit processing,
accounting for as much
as 10 percent of the
total wastewater flow
and 40 percent of the
total biochemical oxygen
demand. In conventional
peeling, the peel is
pre-softened by contact
with dilute sodium
hydroxide and then
removed from the peach
by high pressure sprays
using large amounts of
fresh, potable water.
Water from the peeling
operation therefore
contains essentially all
of the removed peel.
Dry caustic peeling
in which mechanical
rubbing is used to
remove the softened
peel was originally
developed for the
potato processing
industry: however softer
fruit such as peaches
required the development
of a new process.
The modified dry
caustic process discussed
in this report uses
rapidly rotating rubber
discs to mechanically
wipe the caustic treated
peel from clingstone
peaches. A final rinse
to remove the last traces
of peel and caustic is
the only fresh water use.
During this EPA
demonstration grant
with the Del Monte
Corporation water usage
in the peeling operation
was reduced from 850
gallons of water per ton
of peaches to 90 gallons
per ton by dry peeling.
The dry caustic peeling
process also allows for
collection of the peel
as a pumpable slurry.
This slurry may have
potential value as an
animal supplement or
in reclaiming marginal
farm land. Because the
peel is not carried in the
wastewater flow, the total
organic and suspended
solids loading of the
wastewater from the
peeling process is
reduced by about 60
percent. Peach quality
was judged to be equal
to that of conventionally
peeled peaches.
This report covers two
seasons of evaluation
during which the dry
caustic peeling system
was operated in parallel
with a conventional
peeling system at the
Del Monte, San Jose,
California Plant #3.
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Discs rotate at a speed
of approximately 325
RPM. The rotating action
also transports the fruit.
The length of peeling
time is controlled by
adjustment of the upward
slope of the rotating disc
unit and the length of
the peeling unit section.
A tank beneath the discs
collects the peel and
caustic residue as a
slurry, which is pumped
to a solid waste hopper.
Following the disc
unit, peeled peaches are
dropped into a rinse tank
and removed from the
tank by a flight conveyor.
In the demonstration unit,
three manifolds of fresh
water sprays mounted
above the elevator
conveyor remove residual
peel and caustic residue,
and provide make-up
water for the rinse tank.
Each manifold has four
spray nozzles, delivering
approximately one gallon
of fresh water per minute
per nozzle. Water level
in the rinse tank is
controlled by an
automatic sensing device.
A bleed stream from the
rinse tank, equivalent in
volume to the nozzle
flow, is the only effluent
from the unit Rinsed
fruit is conveyed to an
inspection station and
then to the next stage
in canning.
TO CUP-UP
SHAKER AND
INSPECTION BELT
fiJNSEHMTER
TOBlOLOaCAi.
TREATMENT SYSIfM
SAMPLE BOTTLE
Figure 1. Schematic-dry caustic peeler
1 16 "R Ilypvall
Material- Black Ruttfi-SO Dinomeiei- Food Grade
Figure 2. Flange Disc Detail
Malftial' Black Rubber-50 Dv.
Figure 3. Stub Disc Detail
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The most striking
result of the commercial
tests of the dry caustic
peeler is the 90 percent
reduction in water use
as compared to the
conventional caustic
peeler. Significant
pollution parameters can
be reduced by
approximately 60
percent. Table I illustrates
the average wastewater
volumes and pollution
loadings for each process,
based on 24-hour
composite samples taken
on each of the 21 days
of the demonstration
period.
Table II summarizes
the characteristics of the
peach peel solid wastes.
The relatively high pH
of the slurry and the low
pH of the rinse water
indicate that most of the
caustic is removed with
the peel.
':..-.••i-:----:,:'i-^y.:;" • ;'.- TABLET ' ; • . • .,•; .. . • "... .
..:. Comparison of-the Average Liquid Effluent from the Del Monte Dry
: Caustic: Demonstration Project with .Conventional Caustic. Peeling: ,
• All liriits in. Ibs/ton -of peaches unless otherwise rioted .. : .:
Conventional
Caustic
.Suspended :$ollds.
Total Solids :::,
• 850 'gals/ton1. -X:-'
l:O.S.{150Qppm).
:: 6^940 :ppm).
,:.5.6,(79Q:,ppm)..
:;17.8,f25p0ppm),
"
-.-,;•.;'. Dry.. -::
Caustic
•; Peeling
•90 gals/ton
2;a (3700
,1.9{25QO.pprn).
4;0;{53Clb:.ppm):
4.6 :.,-•:•:• ••. -,'•:•••
.cpunterc.urrerit rinse; :iVithout a'':cciu'n:1:ercurrent ..rinse, -this'.
number. ;e6tild; beVeis high as ;20(Jd gals/foh-peafehes^; ,; :;":- ;.."• .:;:
(lon'Peac'hes).
.f:^t^;So
pH'Range-
•74-1.
;9-ir
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conventional peeler at
the Del Monte, San Jose,
California plant. During
these two operating
periods, capacity and
performance of the dry
system has been
continually improved.
Additional operation may
further enhance the
economics.
Not included in these
economics is a reported
1-2% loss of canned
peaches due apparently
to over peeling in the
dry system. This problem
indicted in the first
season was attacked by
reducing the
concentration of caustic
spray and by adjusting
the belt drive to give
increased throughput
(from 12 TPH to 20
TPH). At the end of the
second season, however,
there was still a
reported loss.
The following numbers
can be used for
comparison with either
existing conventional
peeling costs or new
installations. The canner
must factor in his local
surcharge and obtain
a cost (or credit) for
solids disposal at his
locality for his specific
comparison.
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A commercial dry
caustic peeler operated
successfully on freestone
peaches during the 1972
season at Delmar Foods
in Watsonville, California.
The same equipment
manufacturer has sold
two additional peelers
which will be operating
in the 1973 season on
freestone peaches.
There is additional
economic incentive
for use on freestone
{as opposed to
clingstone) peaches,
since the mechanical
action of the wiper
effectively removes
bruises and decreases
the higher cost of hand
inspection associated
with freestone peaches.
Two additional
equipment manufacturers
have also sold dry
peelers for freestone
peaches which will be
in operation in the 1973
season and are now
offering dry caustic
peelers for clingstone
peaches.
Dry Peeled Peaches to Inspection Station
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