Agriculture Reference
In-Depth Information
Canning of meats
Corned beef is perhaps the best known of the canned
meat products, although considerable quantities of
canned ham, ox, sheep and pig tongues and spiced hams
are now manufactured. The preparation of corned beef
will illustrate the procedure normally adopted in the
preparation of canned meats.
ham which will have potentially a greater bacterial flora.
The cans should be stored at 0°C.
Foods packed in glass
A great variety of foods is packed in hermetically sealed
glass containers, and though the treatment of these dif-
fers somewhat from foods packed in cans, the principles
of preservation are the same. The disadvantages of the
glass container are that its greater weight, fragility, less-
ened output for the same amount of equipment and
labour, together with the extra expense in packing, limit
its use for the higher-grade products. On the other hand,
it is less susceptible to attack by the product it contains
and the contents may be readily inspected. The metal
caps of glass containers are usually lacquered tinplate,
with a paper liner inside to prevent discolouration result-
ing from corrosion of the metal. The cap is held firmly
against a rubber gasket on the rim of the glass container
and thus forms a hermetic seal.
Glass-packed foods are processed for a longer period
than canned foods but at a lower temperature, as there is
risk of fracture of the glass, and both heating and cooling
must therefore be carried out more slowly. The modern
method is to process in pressurised steam-heated water. At
the conclusion of processing, the steam is shut off and cold
water is slowly admitted to the retort, but the air pressure is
still maintained to prevent the cap from being blown off by
the internal pressure which develops in the container.
Corned beef
Corned beef is prepared from beef pickled in salt, nitrite
and sugar; boiled for 1 hour; and then trimmed of soft
fats, tendons, bones and cartilage. The texture and the fat
content depend on the taste of the country for which it is
intended, some countries preferring a lean corned beef
and others a higher fat content; that for the UK market
generally contains about 10% fat. Pickling is essential, for
without it the meat after processing would be very much
shrunken and dark in colour, while the can would con-
tain liquid and dripping. The meat is machine cut and
packed automatically into cans. The shrinkage from
original fresh boneless meat to its weight when finally
packed is 40-45%. The cans are then capped with the
vent open and sealed under a vacuum. In some cases,
exhaustion is carried out, with the vent open, in a process
retort for 45 minutes at 104.6°C; the can is then removed,
and the vent is closed as soon as it ceases blowing.
Subsequent processing varies in different plants. In
some cases, the cans are put into retorts and processed at
a pressure of 0.632 kgf/cm 2 for 2½ hours or more,
depending on the size of the can. A 450 g tin of corned
beef requires 21½ hours at 104.6°C, a 2.5 kg tin 5 hours
at 105.5°C, and a 6.3 kg tin 6 hours at 108.3°C. In other
cases, the cans are immersed in boiling water for 3½-4
hours. Processing is followed by cooling, degreasing and
lacquering.
Spoilage in canned foods
It was at one time thought that the keeping qualities of
canned goods depended upon the complete exclusion of
air. Later, it was suggested that the heating destroyed all
micro-organisms, while the sealing of the can prevented
the entry of others, and that decomposition, when it
occurred, was due to faulty sterilisation or to the entry of
bacteria through a fault in the can. Neither of these views
expresses the whole truth because living bacteria can
often be found in sound and wholesome food, and bac-
teriological methods show that any canned meats or
meat products contain living organisms, even after mod-
ern processing methods. The mere presence of living
organisms is of little or no significance in assessing the
soundness of canned goods.
The organisms responsible for spoilage in canned goods
may be spore forming and therefore resistant to commer-
cial processing, or they may be non-sporing organisms
which gain access via leakages after processing. Aerobic
spore-forming bacteria may be present in sound samples
of canned goods. Spores probably remain dormant under
the anaerobic conditions of a properly sealed can but, if
supplied with air through faulty sealing, may develop and
produce enzymes which decompose the foodstuff.
Canned hams
Hams are boned by hand and forced into a pressure
mould to produce the required shape. The metal
container for hams is double seamed, though without a
rubber gasket, sealing being done by hand soldering fol-
lowed by exhausting and soldering of the vent hole. The
hams are finally cooked without pressure at 93.5°C for
several hours. Cooking at a higher temperature for a
shorter time in a pressure retort is contraindicated, as it
produces deleterious changes in the ham texture and
heavy weight loss due to exudation of fat and gelatin. An
increase of only 10 minutes in cooking at these higher
temperatures can increase the overall cooking loss to 5%.
Large hams 1.4-7 kg would be unpalatable if cooked at
normal canning temperatures and should be subjected
to 80°C for up to 60 minutes. This produces a 'pasteurised'
Search WWH ::




Custom Search