Agriculture Reference
In-Depth Information
Figure 10.5
Multi-phase controlled atmosphere stunning (Reproduced with permission from Stork Poulty Processing, Boxmeer, The Netherlands).
Neck cutting
This should be carried out within 15 seconds of the bird
emerging from the stunner. Mechanical neck cutting is
the norm for broilers when the bird's head is guided
across a single revolving circular blade or between a pair
of revolving blades. Accurate positioning of the head is
essential. When cardiac arrest is not produced at stun-
ning, the most humane method of producing rapid brain
death is to sever both carotid arteries. In practice, this is
difficult, but not impossible, to achieve without having
an effect on the further processing of the carcase.
Decapitation is also becoming popular followed by
head maceration.
Where a mechanical killer is used in the United
Kingdom, it is mandatory to have an operative present to
manually kill any bird which has missed the automatic
system. Operatives who kill the birds have to be licensed
by the local authority (Fig. 10.9).
Birds are killed manually by passing a knife across the
side of the neck at the base of the bird's head, which
should sever a jugular vein and carotid artery. Again, it is
better to sever both carotids, but care has to be taken to
avoid damage to the carcase.
Whichever method is used, a sharp instrument is
essential. Automatic killing of turkeys has not been
introduced because of the problem of major variation in
bird size within the flock.
and other birds. The birds, on the conveyor, pass through
a bleeding tunnel, the blood being collected and pumped
into a holding tank.
The birds are scalded either by immersion in hot water
or by spray scalding. Spray scalding is more hygienic but
also more expensive, and therefore, scald tanks are more
commonly installed. The temperature of the water is
dependent on the type of final product. For the fresh,
chilled market, a soft scald of 50-53°C is used as this
does not damage the skin, thereby preventing discolora-
tion and drying (barking) on air chilling (Fig. 10.6).
For the frozen market, a hard scald at a higher tem-
perature, 56-58°C, is used as this facilitates feather
removal and the birds need only remain in the tank for
2-2½ minutes instead of 3½ minutes for the soft scald.
In the United States, there is a statutory requirement for
an overflow from the scald tank of about 1 L/bird for
hygiene reasons. Various chemicals can be added to
assist feather removal and to try to prevent cross-
contamination (but see the following text).
The scald tank immersion results in large numbers of
organisms being released into the water; in addition, fae-
cal material in the tank dissociates to form ammonium
urate and uric acid, which form a natural buffer system,
thereby maintaining scald tank pH at around 6, the point
at which salmonellas are most heat resistant. The overall
effect is that salmonellas, campylobacters and other
organisms, including spores, can survive. Research has
shown that the addition of quaternary ammonium,
acetic acid, etc. to the scald tank would adjust the pH,
the principal controlling factor in the survival of salmo-
nellas and campylobacters, and therefore improve the
Scalding and defeathering
The minimum time for bleeding between neck cutting
and entering the scald tank in the United Kingdom is 2
minutes for turkeys and geese and 1.5 minutes for chickens
