Agriculture Reference
In-Depth Information
Figure 10.6
Aeroscalding - scalding without immersion into scalding (Reproduced with permission from Stork Poulty Processing, Boxmeer,
The Netherlands).
hygiene. At present, this cannot be used because of the
requirements to demonstrate no carcase residues and to
use only potable water.
There is no doubt the operation of scalding from a
hygiene standpoint is fraught with hazards; the tempera-
ture of the scald water, type (immersion, spray with hot
water or steam), duration of scalding, static, agitated or
countercurrent bathwater, type of tank(s), etc. all affect
the degree of water bath contamination. Work by Slavik
et al.
(1995) on the numbers of
Campylobacter
and
Salmonella
on chicken carcases scalded at three different
temperatures would appear to confirm that the higher the
temperature, the greater the contamination (Table 10.2).
Alternative methods of scalding are being devised to
improve the situation. Lower bacterial contamination has
been achieved with spray scalding and plucking in a sin-
gle operation (Veerkamp and Hofmans, 1973). Clouser
et
al.
(1995) found that a spray scalding system for turkey
carcases was superior to traditional scalding (Fig. 10.6).
Improvements in immersion scalding have been made
by stirring the water in order to achieve an ideal mixing,
division of the scald tank into several smaller ones and
high-pressure (800 bar) treatment of scald water. All these
have shown improvements in scald water quality. Lowering
the pH with organic acids may affect product quality, and
the addition of trisodium phosphate may cause corrosion
of equipment. The ideal solution has not yet been found.
Table 10.2
Numbers of Campylobacter and Salmonella (log
mpn/carcase) on chicken carcases scalded at three different
temperatures
Bacterium
Scald
Trial
Temperature (°C)
Trial
1
2
3
Salmonella
52
3.00
3.17
3.09
56
3.16
3.17
3.34
60
3.50
3.48
3.36
Campylobacter
52
3.64
3.30
4.18
56
3.39
2.94
3.39
60
4.08
3.59
3.98
Source: From Slavik
et al.
(1995).
or discs, with attached rubber 'fingers. Rubber flails
mounted on inclined shafts are sometimes used for
finishing.
The machines should be close to the scald tank and to
each other to lessen the effect of cooling. Generally, birds
which have been scalded at higher temperatures require
50% less defeathering capacity. The machines are adjust-
able to allow for differing bird sizes, and this must be
carried out to prevent mechanical damage to the carcase.
Continuous water sprays are usually incorporated
within the machines for flushing out feathers. Feathers
are commonly taken to a centralised collection point via
a fast-flowing water channel located below the machine.
Dry feather systems using a conveyor belt in conjunction
with a vacuum or compressed air arrangement are
Defeathering
Feathers are removed mechanically, immediately after
scalding, by a series of online plucking machines. These
consist of banks of counterrotating, stainless steel domes
