Meat hygiene practice - Gracey's Meat Hygiene - page 180

There must be a waste water disposal system which
hygienically removes waste water and a laboratory to
carry out the required testing or of the services of an out-
side agency.
Containers, equipment and vehicles used for the
transport of animal by-product must be cleaned, washed
and disinfected after use.
Personnel wWorking in the unclean section must not
enter the clean section without changing their clothes
and footwear. Equipment and utensils must not be taken
from the unclean to the clean area.
Waste water originating in the unclean section must
be treated to ensure no pathogens remain.
There must be a systematic method to prevent the
ingress of birds, rodents, insects or other vermin.

weak acid, the hides are tanned. Tanning may be done by
a vegetable process using the barks of trees, or by a
chemical process known as 'chrome tanning. The tan-
nery process, from raw hide to finished leather, takes
about 3 months. The hide from bullocks and heifers,
when tanned, is used as sole leather or for belting. Sole
leather is obtained from the butt, the area of the hide
lying on either side of the backbone.

Hygiene requirements for animal by-product
processing establishments
The premises of the processing plant must be adequately
separated from other processing establishments such as
meat plants. Premises for the processing of high-risk
material must not be on the same site as meat plants,
unless in a completely separate part of a building. Only
authorised personnel should be allowed access.
The establishment should have a clean and an unclean
section, which must be clearly separated. The unclean
section must have a covered area to receive the animal
waste and must be constructed so that it is easy to clean
and disinfect. Floors must be laid to facilitate the drain-
ing of liquids. The plant must have adequate lavatories,
changing rooms and washbasins for staff. In the unclean
section, where required, there must be adequate facilities
for de-skinning or de-hairing of animals and a storage
room for hides.
The establishment should be of sufficient size and have
enough hot water and steam to process hygienically the
waste received. The unclean section must, if appropriate,
contain equipment to reduce the size of animal waste and
equipment for loading the crushed animal waste into the
processing unit. A closed processing installation is
required in which to process the waste, and where heat
treatment is required, this installation must be equipped
with measuring equipment to check temperature and, if
necessary, pressure at critical points, recording devices to
record continuously the results of measurements and an
adequate safety system to prevent insufficient heating.
To ensure that there is no cross-contamination of fin-
ished processed material by incoming raw material,
there must be clear separation between the area of the
plant where the incoming raw material is unloaded and
processed and the areas set aside for further processing
of the heated material and the storage of the finished
processed product.
There must be adequate facilities for cleaning and dis-
infecting the containers in which animal by-product is
received and the vehicles in which it is transported. The
wheels of the vehicles carrying high-risk material must
be disinfected before departure or before leaving the
unclean section of the processing plant.

Rendering processes
While some meat plants have rendering departments for
the treatment of condemned and other inedible material,
it is better, from a public health standpoint as well as the
efficiency of processing, that the premises should be
located away from food outlets and be large enough to
handle material from a large area.
The best and most economical method of processing
unfit meat and offal is by heat treatment in a jacketed
cylinder, which gives complete sterilisation and maxi-
mum return from the rendered material. A number of
different methods are available for handling inedible
material, all of which are concerned with the separation
of the three main constituents, fat, water and fat-free
substance, and the production of sterilised technical fat
and meat-and-bone meal.
There are four categories of rendering systems which
are as follows:

1 Conventional batch dry rendering with mechanical
defatting
2 Continuous dry rendering with screw press defatting
3 Semi-continuous wet rendering with centrifugal
defatting
The batch systems are more labour intensive but less
expensive to install than continuous systems.
In these three systems, the raw material is cooked to ster-
ilise the components (water, fat and meal) for separation,
the fat being finally purified. There are major differences
in the type and order of the various operations.
In the continuous dry rendering process (which resem-
bles batch dry rendering except that the operation is
continuous), the system operates at atmospheric pres-
sure. After cooking, the material is pre-strained and
discharged to a screw press for defatting. The length of
the cooking process depends on the method of filling
and the cooker size.