Plant sanitation - Gracey's Meat Hygiene - page 88

coatings. Carbohydrate deposits can vary from soft and
powdery to quite hard.

The soil
In a meat plant, the most common 'soils' or deposits
originate from the animals themselves and from any
other ancillary additives or components used in the
manufacturing process. These product-derived soils
include the following:

Miscellaneous deposits
Other soils may originate not from the food production
process itself but from water, surface corrosion, vehicles
and other outside materials. Such deposits include:
• Limescale from water drips and leaks or in hot water
systems, tanks, cooking kettles, etc.
• Corrosion deposits of steel, zinc, aluminium, brass, etc.
• Rubber marks from forklift trucks
• Adhesives from labels
• Inks and dyes from stamps
• Algae in moist areas with high condensation
• Fungi in cold moist areas, especially near chills and
freezers and in silicon sealants throughout the plant

Fats, oils and greases
These are often triglycerides of fatty acids and can vary
from waxy solids to liquids. They are insoluble in water
and can vary in their structure and properties, depend-
ing on their origin, differing between different body
parts of the same animal species, between animals of dif-
ferent age and between different species. Poultry evis-
ceration fats are very waxy and difficult to remove, for
example, compared to beef tallow. Fats, oils and greases
can change when exposed to air for some time (particu-
larly those containing unsaturated fatty acids) and may
oxidise or polymerise to become harder and more closely
bonded to the surface. Exposure to very high tempera-
tures, such as in ovens, will cause fats to carbonise and
bond tightly even to stainless steel surfaces. Fatty or
greasy deposits can be recognised by their greasy feel
and water repellence, and when aged and oxidised to a
moderate degree, they take on a cheesy opaque nature,
which can be scraped easily with a fingernail. Fully poly-
merised oils can become almost plastic in feel and hard-
ness. This effect is utilised when linseed oil is applied to
cricket bats.

These deposits may or may not present hygiene risks in
themselves but are at least unsightly and at worst can act
as absorbent and supportive substrates for other soils or
micro-organisms. Chemically, they are very different
from each other and may therefore need very different
cleaning approaches. This is especially true because mul-
tiple types of soil are found frequently in the same plant,
often combined in the same deposits. Physically, this
usually makes them harder, more adherent and more
difficult to remove. Just like sand and gravel, they rein-
force cement to make concrete. It is important, therefore,
to identify the soils present in each plant area by their
origins and by their appearance. Only then is it possible
to design the correct cleaning regime.

Proteins
These complex, large molecules are normally too large to
dissolve easily in water. They have a specific shape that
may change when exposed to high temperatures, a pro-
cess known as denaturation, usually making them harder
and insoluble. The best-known example of this is the
changes seen in heating the white of an egg. This prop-
erty of proteins is important in the processing of foods
and in the selection of rinse water temperature used to
remove protein deposits. In meat plants, bile and other
gut-based soils may give rise to a green or yellow tena-
cious deposit on evisceration equipment. In pig-dehair-
ing equipment, heavy, hard protein deposits are common.
Blood proteins in abattoirs can create particular prob-
lems on porous surfaces, often giving rise to a green/
brown, very resistant staining. Aged protein deposits can
be quite hard, normally not scraping off easily with a
fingernail.

The substrate: Materials of construction
Many different materials may be found in meat plants,
and while none is perfect, they do vary considerably in
their ease of cleaning and their resistance to abrasion
and to corrosion, either by the factory environment itself
or by contact with cleaning chemicals. Smooth, impervi-
ous, abrasion-resistant, non-toxic surfaces are ideal and
required by law (Council Regulation (EC) No 852/2004
and 853/2004), and industry guidelines have also been
developed (EHEDG, 2004).
Stainless steel , of a high grade, is the best choice for
many surfaces but, especially in its cheaper forms, is lia-
ble to pitting corrosion in the presence of chlorine and
stress corrosion/cracking at elevated temperatures.
Mild steel will rust rapidly in moist and salty environ-
ments and should normally be avoided in meat plants.
Zinc (as a sacrificial coating on steel) and aluminium
are both commonly found but are problematical because
of their susceptibility to attack by strong alkalis, acids
and some process fluids. At worst, they can be heavily
corroded, embrittled or encrusted, none of which is
helpful in maintaining hygienic surfaces. As a rule, they

Carbohydrates and starches
These, too, are large molecules, which may be insoluble,
especially after exposure to heat. Their source is usually
plant-derived materials used in producing sauces and