290 Chapter 15
ide, are used to remove heavy burnt - on soil,
encountered in high - temperature processing
such as ovens and smokehouses. These com-
pounds are very corrosive, and inhalation of
the vapors can cause respiratory damage, so
they are used in specialized cleaning opera-
tions such as CIP (Cleaning - In - Place) proce-
dures. The moderately alkaline compounds
(pH 10 – 12), such as sodium metasilicate,
have good dissolving powers and are formu-
lated in detergents to aid the removal of fats
and grease. Mildly alkaline compounds (pH
7 – 10) are used for manual cleaning. An
example is sodium carbonate, which is used
in many manual and heavy - duty detergent
mixtures as a buffering agent and for its
water softening capabilities.
Acid cleaning agents are used particularly
for removal of encrusted residues of dirt or
protein, or inorganic deposits ( “ scaling ” ).
Strong inorganic acids, hydrofl uoride and
hydrochloride, because of their corrosiveness
to stainless steel, are usually used to remove
heavy scale deposits found on steam - produc-
ing equipment or boilers. Organic acids, such
as citric and hydroxyacetic acid, are less
corrosive and are used in manual cleaning
formulations.
In practice, alkaline and acid cleaning
substances should be used alternatively. The
alkaline agent should be the substance used
for routine cleaning, but every few days an
acid substance should be employed instead in
order to remove encrusted residues, scaling,
etc.
A relatively new cleaning method in the
food industry, in particular for larger - scale
plants, is foam or gel cleaning. Water foam
containing detergents and other cleaning
agents is sprayed on wetted walls, fl oors, and
surfaces of equipment. The foam does not
immediately run off but clings to the sur-
faces. It allows a longer - term contact on the
surfaces to be cleaned. After a suffi cient
contact time (min. 15 min), the foam is
washed down with water (usually low - pres-
sure water spray).nonionic surfactants have proved to be effec-
tive against organic matter. Inorganic matter
is most effectively removed by acid cleaning
agents.
Cleaner application can be handled by
using brushes or scrapers for dismantled
equipment, or in general, for smaller surfaces
to be cleaned. Application through a central-
ized or portable high pressure - low volume
system, using 50 ° to 55 ° C water could be a
solution for large surfaces such as fl oor and
wall areas, as well as working tables, con-
tainers, and equipment. The pressure should
be between 30 – 70 bar and the spraying
nozzle ≤ 15 cm from the surface to be cleaned;
otherwise, the pressure being applied
decreases rapidly. If hot water is used, the
temperature should be 55 ° C at the nozzle, in
order to achieve suffi ciently high tempera-
tures at the surfaces, in particular for fat
removal.
Soak time prior to rinse - down should not
exceed 20 minutes.
To be effective, detergents should be able
to wet and penetrate soil, emulsify fat, dis-
perse and suspend soil, and counteract water
hardness. In addition, they should prevent
soil from redepositing on clean surfaces and
be noncorrosive to equipment. No single
detergent combines all these traits, so formu-
lations of compounds are tailored for each
type of cleaning operation. Commercially
available cleaning agents in modern cleaning
practices are complex compositions of alka-
line, acid, or neutral chemical substances. In
order to improve their soil - loosening proper-
ties, surface - active agents, also called surfac-
tants or detergents, are added. Detergents
decrease the surface tension of water, so
water can penetrate into the small spaces
between soil particles and surfaces, where
those particles are attached, thus facilitating
their removal.
Alkaline cleaning compounds are used for
the removal of organic soil, protein residues,
and fats. Strongly alkaline compounds (pH
greater than 13), for example sodium hydrox-