Agriculture Reference
In-Depth Information
Table 8.5
Standards of rendered animal fat, depending on type
Ruminants
Porcine animals
Other animal fat
Edible tallow
Edible fat
Lard and other
fat for refining
Edible
For refining
Premier jus
a
Other
Tallow for refining
Lard
b
Other
FFA (m/m% oleic
acid) maximum
0.75
1.25
3.0
0.75
1.25
2.0
1.25
3.0
Peroxide maximum
4 meq/kg
4 meq/kg
4 meq/kg
4 meq/kg
4 meq/kg
4 meq/kg
4 meq/kg
4 meq/kg
Total insoluble
impurities
Maximum 0.15%
Maximum 0.5%
Odour, taste, colour
Normal
a
Rendered animal fat obtained by low-temperature rendering of fresh fat from the heart, caul, kidneys and the mesentery of bovine
animals, and fat from cutting rooms.
b
Rendered animal fat from the adipose tissues of porcine animals.
Fat occurs in many area of the
pig carcase
, the best quality
fat being obtained from the peritoneal lining (leaf fat) and
the next best from the back fat, mesentery and omentum.
The surplus fat of pigs is worked up into various qualities of
lard. A pig of 90 kg live weight yields about 6.3 kg of lard.
Sheep fat
is rendered in the same way as beef fat or lard
and, though it is not converted into oleo oil or oleo stea-
rin because of its flavour, it may be used as dripping
when blended with other fats. Mutton fat is firmer and
contains more stearin than ox or pig fat, and historically
was used as a preservative layer on the top of glass jars of
meat paste (Table 8.5).
atmospheric pressure to drive off water indirectly from
the fat in the cooker. The rest of the process is the same
as for the wet rendering method.
The
continuous low-temperature wet rendering
system
uses heating, separation and cooling on a continuous
basis, and is usually regarded as the ideal process. The
process involves mincing of the raw material, melting by
live steam injection at 90°C, continuous separation of
solids from the liquid fat in a decanter centrifuge, further
heating, centrifugation to remove the fines and cooling
in a plate heat exchanger to below solidification point.
An important principle in the rendering of fat is the pre-
vention of the breakdown of fat into fatty acids and glycer-
ides by the action of the enzyme lipase, which is active at
temperatures of 40-60°C. Above 60°C, lipase is inactivated.
The continuous low-temperature system utilises this action
and at the same time minimises undesirable chemical
activity, burning, oxidation and off-flavours.
Edible fat rendering
High-quality fats have low FFA values and are usually sta-
ble. Efficient rendering processes ensure that the FFA con-
tent remains low by means of initial cold storage of the raw
material where it is not immediately used, followed by
keeping the processing temperatures as low as possible
and the cooking times minimised. There are three main
methods of processing edible fat: wet rendering, dry ren-
dering and continuous low-temperature rendering.
The
wet rendering
method involves the use of pressure
batch cookers in which the pre-cut raw material is
injected with live steam to a temperature of 140°C under
pressure, for 3-4 hours. After this time, the pressure is
slowly released and the fat is run into a receiver and fur-
ther purified by gravity or centrifugation to settle out the
water and fines. The proteinaceous solids or greaves are
emptied from the cooker, and the fat is removed by pres-
sure. Historically, solvent extraction methods were also
used. Greaves are then ground and dried if intended for
human consumption or used in the pet food industry.
The
dry rendering
process uses heat in the form
of steam and water over a period of 1
1
/
2
hours at
Stomach and intestines
The contents of the rumen, reticulum, omasum and abo-
masum are generally emptied in the gut room and the
intestines are separated from the stomachs. In the United
Kingdom, the bovine intestines and mesentery are col-
lected, along with the other SRM, as animal by-product
Category 1, and stained and rendered accordingly.
Tr ipe
is most commonly produced from the first
stomach (rumen or paunch) and second stomach (retic-
ulum) of the ruminant and occasionally from the third
stomach (omasum). It can also be derived from the
stomach of the pig. The stomachs are first emptied and
washed, and the fat is trimmed off. The pillars of the
rumen (mountain chain) may be removed, trimmed,
packaged and frozen for human consumption, Japan
being the traditional consumer, but also in other
