Plant sanitation - Gracey's Meat Hygiene - page 102

expensive. The design of these positive displacement
pumps causes pressure in the system to drop precipi-
tously if the maximum flow rate is exceeded, for exam-
ple, if one person too many uses an outlet simultaneously
or if one nozzle is missing or worn out. The high velocity
of the water from the nozzles causes the jet to break up at
a distance of about 1 m into a fine mist, which has lost
virtually all its momentum and impact. Rinsing of sur-
faces therefore needs to be carried out at close range.
This is time-consuming for the operators and in addition
causes the soil deposit to be broken up violently, creating
contaminating aerosols. High-pressure water is also dan-
gerous and may penetrate the skin or damage the eyes.
Medium-pressure rinse systems (20-40 bar) are a com-
promise option balancing both pressure and volume.
Using multistage centrifugal pumps and wider-bore,
medium-pressure-rated pipe work, these systems are
vibration-free. Additionally, the latest technology utilises
frequency-controlled motors to prevent start-up 'shock'
and false starts and remove flow variations as different
numbers of users come on to the system. The nozzles
used may be individually selected for foam, disinfection
and rinse (when satellites are in use) with the latter avail-
able in rotating versions and adjustable spray patterns.
As the water velocity is lower and the volume per second
higher, the jet retains most of its impact even at several
metres distance. This means that rinsing can be faster,
with a better sluicing-away effect. The extra water con-
sumption per second is usually compensated for by a
shorter rinse time. Water consumption in total, com-
pared to a high-pressure system, is more or less equiva-
lent, but labour savings (in the most time-consuming
stage of the cleaning sequence) can be significant.

The temperature that gives the best compromise
between effectiveness and economy is 50-65°C, which
is enough to soften the fats encountered in meat plants,
without the drawbacks shown earlier. In fish processing
plants, because of the low denaturation temperature of
the proteins, rinse water at circa 35°C is used. There are
new developments looking at the possibility of reduc-
ing pre-rinse temperatures for more economical COP
and CIP.

Contamination and re-contamination
Meat plant surfaces will be exposed to microbial con-
tamination by direct contact with the exterior of the ani-
mal prior to and after slaughter and to the gut contents
during and after evisceration. The dressing process and
subsequent production stages are designed to reduce
further direct contamination of food product with these
micro-organisms. While viscera are kept physically sep-
arate from edible materials, plant surfaces in evisceration
areas will have high bacterial counts. Personnel and
external material such as pallets, vehicles, etc. also bring
micro-organisms into the plant, especially onto the
floors and into the air. The dispersal of micro-organisms
within a plant is generally well reviewed and has been
previously described (Board, 1983, chap. 3, pp. 57-68).
During cleaning, these micro-organisms, whether
spoilage, pathogenic or harmless, may be disturbed in
such a way as to be transmitted, perhaps directly onto
food product itself or onto previously cleaned surfaces.
This accidental re-contamination is carried by a number
of possible vectors , which, unless understood and con-
trolled, can nullify the effectiveness of the cleaning
procedure.

Water temperatures
Although the EU regulations call for 82°C water to be
used for knife sterilisation, such high temperatures are
impractical for most plant cleaning operations (with the
main exception of CIP) for a number of reasons:
• The steam, humidity and condensation obscure vision
and encourage microbial growth.
• Proteins are denatured on the surfaces and hard-water
scale formation is increased.
• The load on the extraction and cooling systems is
increased.
• Thermal shock can damage surfaces owing to
differential expansion.
• Pipe work lifetime is reduced.
• The lances are too hot to hold and the water jet is
dangerous.
• Energy costs are too high.
• Foam quality deteriorates at very high temperatures.

Air
Air can carry dust from hide-pullers, fleeces, feathers,
etc., especially in dry weather. This dust is likely to con-
tain faecal bacteria, among others. Air can also carry
aerosols (usually a combination of water, soil and
microbes) that have been created, during rinsing, by
washing machines, during boot washing and even dur-
ing hand washing, though the last two produce less dense
lower mobility aerosols than the first two. Aerosols that
contain a high concentration of small particles (<20 µm)
can easily move around the factory via local air cur-
rents and are generally recognised as a significant causal
agent of re-contamination and/or cross-contamination
(Burfoot, 2005). Pseudomonas spp., Listeria spp., E. coli
and Salmonella spp. are frequently found on floors and
drains, which makes the rinsing of these potentially
problematic. Hot water or steam can also create aerosols,
which condense on cold overhead surfaces, later to drip