Agriculture Reference
In-Depth Information
a primary tank and held there until the animal from
which the blood originated has passed meat inspection.
Should the animal not pass post-mortem inspection, only
the small holding tank of blood need be condemned.
In a typical blood meal plant separation of the plasma
and cell fractions is accomplished in the high-speed cen-
trifuge or separator. After separation, the plasma is fro-
zen or spray-dried at low temperature in order to
maintain its solubility and binding properties. The red
cells can be used for black sausages or blood puddings or
dried into blood meal.
It is important to prevent haemolysis or rupture of the
red cell membranes during processing. Haemolysis will
occur if the red cells come into contact with solutions of
lower osmotic pressure, causing the absorption of water
and bursting of the corpuscles, and the presence of fat,
which will dissolve cell membranes, bringing about hae-
molysis. The same problem can be caused by sudden
variations of temperature, freezing and damage through
rough handling.
countries. The remaining material is cleaned in one
stainless steel drum which operates rather like a cylin-
drical washing machine and then transferred to a second
similar machine but on this occasion with a roughened
interior which removes the external fat. The stomachs
are then scalded in water containing washing soda,
scraped and placed in cold water to clean them, and
finally cooked for 3-3½ hours at a temperature of
49-60°C. The reticulum is the source of 'honeycomb'
tripe. In some countries, the omasum is made into 'bible'
tripe; in others, it is considered uneconomical because of
the difficulty of removing the mucous membrane.
Rennet is manufactured from the abomasum of the calf.
Intestines - casing preparation
The first operation in handling intestines is 'running, that
is, the separating the intestines from the mesentery. This is
carried out either manually or by machine. The next step is
to run the intestine through a 'manure stripper' compris-
ing large rollers (which resemble a laundry wringer), to
squeeze out the contents of the intestines. This step requires
the use of a great quantity of potable water to wash the cas-
ings and the correct arrangement and alignment of equip-
ment to ensure control and removal of dirty water from the
process without back flow, to ensure progressive cleaning
of the intestines. The casing should then be soaked in water
for approximately 30 minutes at 38-42°C. In some areas of
the world, casings then go through a fermentation cycle,
but in other countries (e.g. the United Kingdom and the
United States), casings processed by fermentation are no
longer acceptable. Intestines which have not been fer-
mented are run through a crushing machine and soaking
tank. This breaks the intermucosal membrane and sepa-
rates it from the rest of the intestine. Next, the intestine
goes through a mucosa stripper, which looks and acts
essentially like the manure stripper used for the initial
emptying. Potable water at 42°C is again used to wash away
the waste material. Any remaining string-like material and
mucosa are removed by rolling. After cleaning, the casings
are placed in a cold salt solution and held overnight. The
next day they are graded, salted with fine salt until they
have absorbed 40% salt and packed into barrels.
Bones
Bones attached to the musculature are handled and sold as
fresh meat. However, today, because of the increasing pro-
duction of boneless meat, there is an increasing amount of
bone available for processing. Once separated from the
musculature, bone must be processed without undue
delay, with attention to temperature control and of course
hygiene. The end products of bone processing are fat,
bone meal and gelatine, with meat-and-bone meal being
produced when there is meat in the original raw material.
Gelatine is produced from bones, tendons and sinews
subsequent to the extraction of fat and under carefully
controlled pressure. Current EU legislation requires that
ruminant bone material from animals born, reared or
slaughtered in countries or regions classified as having a
low incidence of bovine spongiform encephalopathy
(BSE) is subjected to a process which ensures that all
bone material is finely crushed and degreased with hot
water and treated with dilute hydrochloric acid (at mini-
mum concentration of 4% and pH <12.5) for a period of
at least 20 days with a sterilisation step of 138-140°C for
4 seconds or by any approved equivalent process.
Gelatine is used in making brawn, pies, ice cream and
capsules for medicines, in photography, as a culture
medium for bacteria and in the production of smokeless
gunpowder. Some of the gelatine used for these purposes
comes from veal and a smaller amount from beef.
Nowadays pig skin supplies a large quantity of gelatine.
Blood for human consumption
Approximately 4.5% of the live weight of an animal is
collectable blood, which represents around 10% of the
protein available in an animal. Dried blood is high in
protein (80-90%) and rich in lysine.
Blood for human consumption is collected via a hollow
knife inserted into the blood vessels where sticking is
performed. Normally, an anticoagulant such as sodium
citrate (0.2% w/v) is supplied to the knifepoint through a
hollow pipe in the knife handle. It should be collected in
Hides and skins
Edible products manufactured from hides and skins
include gelatine and collagen. In addition, pig skins are
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