Agriculture Reference
In-Depth Information
Scalded, depilation, scraping and singeing take place
immediately after bleeding is complete. In the smaller
abattoirs, scraping is done by hand, but in large abattoirs
and bacon factories, a mechanical dehairing machine is
used. It is estimated that if there is a regular throughput
of some 200 pigs on 2-3 days/week, a dehairing plant is
necessary. An extraction system, which removes steam
from the canopies over the scalding tanks and keeps the
temperature of the steam raised by heated air, serves to
prevent condensation and fogginess.
A typical pig slaughter operation of up to 650 pigs/
hour would consist of the operations shown in the pork
slaughter flow chart in Figure 3.6.
The following is an example of a slaughter line for
sheep which requires 17 operatives with a potential pro-
duction of 150 sheep/hour:
1
Pen sheep and stun
2
Shackle and hoist
3
Stick
4
De-elevate to crutch conveyor
5-9
Conveyor dressing (remove feet, commence fleece
removal, saw brisket)
10
Elevate to overhead rail
11
Clear tail and commence backing
12
Back and chute fleece
13
Remove head
14
Eviscerate abdomen
15
Wa s h
16
Eviscerate thorax
17
Weigh and tag
18
Final wash
Scalding and dehairing
The factors to be considered relating to scalding and
dehairing are hourly rate of slaughter, size of pig to be
handled, ease of operation of the machines, efficiency of
cleansing and corrosion.
A typical scalding tank is maintained at 60-62°C;
effective scalding requires 6 minutes at 60°C, 5 minutes at
61°C. It is important to contain the steam as completely
as possible and to remove it by efficient extraction in
order to prevent condensation. Consideration should be
given in the design as to the rapid removal of carcases
from the tank in the event of mechanical breakdown or a
carcase becoming stuck in the equipment as the carcase
will quickly cook, particularly the loin/tenderloin, and
will be considered unfit for food.
In the scald tank, before operations begin, there can
be as many as 40 000 bacteria/ml in the tank, rising to
45-800 million organisms/ml after the scalding of 600
pigs. Among these were aerobic and anaerobic spore-
forming bacteria, cocci and organisms belonging to the
coli-proteus groups; of 220 samples of scalding water,
Salmonella paratyphi
and
S. typhimurium
were isolated
on one occasion. It has been discovered that develop-
mental types of
Salmonella
could occur in the sludge of
the scalding water and that a deep infection of the pig
meat can arise from the bacterial flora on the surface. In
addition to micro-organisms, parasites such as
Ascaris
suum
and whipworm (
Trichuris trichiura
), hair, epithelial
cells,
Balantidium coli
and moulds such as
Aspergillus
and
Mucor
may be found. Many of these can gain entrance to
the lungs and to the area of the stab wound.
The feet should be removed with a special instrument,
avoiding the usual practice of individual removal with
the skinning knife and the all-too-frequent littering of
the floor with these parts.
The New Zealand Meat Industry Research Institute
(MIRINZ), in the 1980s, developed a method of
automatic
pelt removal
to produce blemish-free and hygienic car-
cases with the minimum of labour which is now widely
used. The valuable hindquarter is completely untouched,
and there is no stretching of the pelt. Termed the 'inverted'
method, the carcase is suspended by the forelegs or in a
near-horizontal position on twin conveyors. A 'Y' cut is
made from forelegs to throat releasing the 'vee' flap, which
is fed into the brisket skinner to clear the foreleg pockets.
The two shoulder flaps are then pulled down, and the 'vee'
flap is split by hand. The head is removed and discarded
under veterinary control. The pelt is further prepared for
automatic removal by skinning the belly and groin. The
carcase is now ready for the operation of two pelting
machines - the shoulder puller and the final puller, the
former drawing the shoulder flaps in a downward/back-
ward direction, while the latter (a hydraulically operated
arm and clamp) grips the fleece centrally and strips it
downwards off the hindquarter and shanks. The fleece is
then released through a floor chute to the pelt room.
Pig slaughterhall
A pig slaughter line built to handle pork pigs is generally
not suitable for sows and boars. This should be borne in
mind at the planning stage.
The scalding, depilation, scraping and singeing of pig
carcases are inherently dirty processes. This usually
makes it necessary to physically separate these processes
from evisceration in order to ensure hygienic operation.
Vertical scalding
Vertical scalding of pig carcases involves the use of a
double-walled tunnel in which steam, generated from a
water bath in its bottom, is blown over the carcases and
through a ventilator located over the condenser. The
temperature in the tunnel is controlled by a thermostat
at 61-64°C. The cooling water from the condenser in
