Preservation of meat - Gracey's Meat Hygiene - page 67

appear to be affected by the type of scalding equipment.
Vertical scalding of pigs on the line in a 'steam cabinet'
reduces the opportunity for contamination of the carcase
via the stick wound. After dehairing, the carcase is hoisted
onto a greased skid rail and transferred to a singeing
plant, which consists of two vertical half-cylinders lined
with heatproof bricks. The carcase is singed by a fired
combination of oil and air or by gas burners at a tempera-
ture of 1300°C. Temperatures on the skin surface vary,
but thermal imaging studies have demonstrated a range
of carcase surface temperatures immediate after full body
singeing between 100 and 200°C.
Singeing colours the skin brown, removes any hairs still
remaining, hardens the subcutaneous fat, enhances the
keeping quality of the meat and sterilises the external
surface of the pig so that following effective singeing the
bacterial load on the carcase surface has been completely
removed Berends et al. (1997). On leaving the furnace, the
carcases are sprayed with cold water and scraped and
polished in a tunnel containing banks of stainless steel
scrapers and nylon brushes until the burnt brown epider-
mis has been removed and the pig appears white. These
procedures, however, recontaminate the surface of the car-
case to the order of 10 4 bacteria/cm 2 . Bolton et al . (2002)
suggested the process could result in an overall reduction
of contamination of the order of 3 log units/cm 2 .
The majority of these are spoilage bacteria, predomi-
nantly acinetobacteria, moraxellae and pseudomonads ,
with enteric organisms such as E. coli and Campylobacter
at single figures per cm 2 .
The carcases are then ready for evisceration, inspection,
weighing and grading followed by immediate transfer via
overhead rails to the chills where they are chilled to <4°C
within 24 hours.

femur and a part of the sacrum known as the oyster
bone. The pelvic bones are removed and the gammon is
trimmed.
The spinal column, or chine bones, is removed using a
circular saw, and the middle is slit into belly and back
cuts. The ribs may be removed individually, by a process
known as single ribbing, or in sheets. Finally, excess fat is
trimmed off, and in most cases, the rind is removed.

Application of the pickle
Salt for the cure may be kept in a large silo through which
water filters to produce a saturated salt solution. This is
chilled to −2 or −3°C and nitrite added to a concentra-
tion not exceeding 150 mg/kg. Usually, nitrate is not used
as a constituent of the pickle. This is because nitrate is
only effective in so far as it is converted into nitrite by
bacteria present in the cover brine. Sodium ascorbate is
added as a source of ascorbic acid, a reducing agent,
which aids the formation of nitrosomyoglobin and hence
ensures that the bacon or ham has good colour forma-
tion and stability. In a maple cure, sugar, maple crystals
and seasoning give the bacon a unique flavour.
Polyphosphates aid water retention in the cured meat
during the cooking process, so reducing shrinkage dur-
ing cooking, making the hams more succulent and
improving the texture of smoked product.
The amount of curing salts which can be used is regu-
lated in the United Kingdom by the Miscellaneous Food
Additives and Sweeteners in Food Regulations 2007,
implementing recommendations from EFSA 2003. The
legislation restricted the amount of sodium nitrite that
can be used as an input to 150 mg/kg, which is equivalent
to 178 mg/kg of potassium nitrate. For sterilised meat
product, the input is reduced to a level of 100 mg/kg of
sodium nitrite equivalent to 123 mg/kg potassium
nitrate. Exceptions are made for some traditional
processes, such as traditional immersion-cured prod-
ucts, including Wiltshire hams, and traditional dry-
cured meat products. Permitted levels for these products
vary and are based on levels of residue rather than input
levels. As an example, the maximum residue limit for
Wiltshire bacon or ham is 250 mg/kg of nitrate.
This was in recognition that nitrites can react with
secondary and tertiary amines to form nitrosamines,
which are carcinogenic. Earlier methods of curing, by
hand injection of pumping brine (called stitching)
followed by immersion of the sides in cover brine for at
least 4 days, have largely been superseded. The brine or
pickle is now introduced into all sides of the prepared
cuts by automatic pumping machines which introduce
pickle under pressure through needles approximately
2 cm apart. The addition of pickle increases the weight of
the piece by approximately 10%.

Cutting
Under modern systems, very few Wiltshires (full sides of
bacon) are produced, it being more common to reduce
the side to individual primal cuts before curing. The
butchery processes vary but generally commence on
removal from the chillers with the removal of the head
and forelegs while the pig is still suspended on the over-
head rail. This produces two sides which are dropped
onto a moving steel conveyor, before the removal of the
jaw flap from the fore. The hindleg is cut midway through
the hock, and the fore-end is removed by a bandsaw at
the level of the third and fourth rib. The fillet (also
known as the tenderloin) runs from the third most pos-
terior rib back along the dorsal surface of the abdominal
cavity to the gammon. This is carefully removed, and any
loose pieces of meat, for example, the diaphragm, are
trimmed off the side. The gammon, the hindleg, is
removed by a bandsaw, midway between the head of the