Agriculture Reference
In-Depth Information
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Figure 4.3 Stages of can manufacture (by courtesy of Metal Box Ltd).
filling of the can, to remove gases and to prevent oxidative
changes which might cause deterioration. A firm, dry
pack is required for meat foods without any excess of free
liquor in the can; the moisture content of meat is there-
fore reduced by parboiling in steam-heated water, which
produces up to 40% shrinkage in corned beef, 32% in
ox tongues and 30% in pork tongues. Highly fattened
animals are unsuitable for corned beef, as the meat is too
fat and the finished product has an objectionable taste
and appearance. The meat is therefore obtained from
cattle which are older and leaner than those furnishing
the supply of chilled or frozen beef.
After meats have been parboiled, they are taken to the
trimming table where inedible parts such as bones,
cartilage and tendons, together with surplus fats, are
removed.
Filling
It is important that the correct weight is filled into each
can. Overfilling can result in underprocessing and
distortion of the can's seams. Underfilling may result in
air pockets within the product which may interfere with
the transfer of heat by conduction during processing.
Any delay between filling and processing may allow bac-
terial growth with a resulting loss of quality.
Exhausting
Exhaustion is necessary for the following reasons: to pre-
vent expansion of the contents during processing, which
may force the seams; to produce concave can ends so that
any internal pressure may be readily detected and warrant
rejection of the can; to lower the amount of oxygen in the
can and prevent discolouration of the food surface; and, in
fruit packs, to reduce chemical action between the food
and container and to avoid hydrogen swells. Although the
production of a vacuum probably has little effect on
micro-organisms, experience has shown that tins contain-
ing a vacuum keep better than those with air in.
Exhaustion of a can may be carried out in two ways:
Canning operations
Cans may be filled either by hand or by automatic
machinery, the next process being exhaustion or removal
of air from the can before it is sealed. When meat with
gravy is being canned, it is important to put the gravy in
first in order to ensure freedom from air bubbles, which
could aid bacterial growth. It is essential to make sure the
cans are not being overfilled.
1 Heat exhausting , in which the contents are filled cold into
the can, which is then passed through a steam-heated
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