Agriculture Reference
In-Depth Information
It is common practice, particularly in New Zealand, to
wash the carcases after pelting and before evisceration to
remove visible contamination such as wool, blood and
faeces. It is likely that, although this practice improves
the appearance of the carcase, it actually assists in spread-
ing contamination to otherwise clean parts of the carcase
and adds water to the warm exposed meat surface to
assist bacterial metabolism.
Bell and Hathaway (1996) found that the areas of
highest contamination were the forequarter region
with inverted dressing and the hindquarter with con-
ventional dressing. In both cases, these regions are the
sites where cuts are made through the skin. With both
systems, contamination around these cuts was entirely
consistent with direct fleece contact resulting from
'rollback.
In Italy, mechanical subcutaneous inflation has been
used to assist in skinning lightweight lambs. Producers
claim that the resultant carcase has a better appearance
and that there are fewer cuts in the subcutaneous fat and
muscle. The technique has been shown to produce
carcases of comparable microbiological standard to
those produced by conventional dressing. Sheridan
(1998) suggested that washing the carcase after the hide
or fleece has been removed and before evisceration
reduced the pathogen load on carcases at the end of the
dressing process.
Figure 8.5
Vertical scalding of pigs with humidified air.
no water in lungs, no infection of thorax through
the stick wound and no recirculation of dirty water
(Fig. 8.5).
Following singeing, the bacterial load on the carcase
surface is of the order of tens of bacteria/cm
2
, but the
scraping and polishing procedures which follow re-
contaminate the surface to the order of 10
3
bacteria/cm
2
.
The majority of these are spoilage bacteria, predomi-
nantly acinetobacteria, moraxellae and pseudomonads,
with enteric organism such as
E. coli
and
Campylobacter
at single figures per cm
2
.
An apparatus, described by Gill
et al
. (1995), has
been developed and trialled commercially on a pig line
operating at 800 pigs/hour, and is capable of reducing
the contamination on the surface of uneviscerated pigs
by a factor of 10
2
. The machine washes the pigs with
sheets of water heated to 85°C for a treatment time of
15 seconds. Water is recirculated from a tank beneath
the line through screens to header tanks which feed the
nozzles.
One common problem, or perceived problem, is the
failure of the automatic equipment to remove all of
the pig's
toe nails
all of the time. Although they look
dirty, personal investigation would suggest that toe
nails carry no greater a bacterial load than the rest of
the carcase.
Pigs
Most pigs in the British Isles are scalded, de-haired,
singed and scraped as a preparation for bacon produc-
tion rather than being skinned. The scalding water may
contain many different types of bacteria originating
from the pigs' skin and gastrointestinal tract, including
Salmonella
spp. The temperature of the water in the
drag-through scalding tank, at 60°C, is generally suffi-
cient to reduce vegetative growth and can result in as
much as a 4 log reduction in bacterial numbers on the
surface of the carcase. If, however, the temperature of the
scald water is not properly maintained, contamination of
the water with enteric bacteria may reach 2 log units/ml.
The skins of scalded pigs were found to have low num-
bers of both enteric pathogens and spoilage bacteria
(Sorqvist and Danielsson-Tham, 1986; Troeger, 1994),
but the subsequent de-hairing process re-contaminates
the skin.
Vertical scalding of pigs
on the line with humidified
air reduces the opportunity for contamination of the
carcase via the stick wound. Humidified air is blown
under pressure through nozzles to reach all parts of the
carcases. Scalding at a temperature of 61°C continues
for about 7 minutes. Water consumption is about 15% of
the normal method. There is no cross-contamination,
Preventing contamination from the
gastrointestinal tract
After the outer integument, the gastrointestinal tract is
the next most important potential source of contamina-
tion. However, if the rectum and oesophagus can be
sealed, and the tract removed intact, the contamination
can be effectively controlled.
