depends on the humidity, temperature
required, and length of time a given temper-
ature must be maintained. Microorganisms
can be destroyed with the correct tempera-
ture if the item is heated long enough and if
the dispensing method and application
design, as well as equipment and plant
design, permit the heat to penetrate to all
areas. Temperature should be measured with
accurate thermometers located at the outlet
pipes to ensure effective sanitizing. The two
major sources for thermal sterilization are
steam and hot water.
Steam
Sanitizing with steam is expensive and usu-
ally ineffective. Workers frequently mistake
water vapor for steam; therefore, the temper-
ature usually is not high enough to sterilize
that which is being cleaned. If the surface
that is being treated is highly contaminated, a
cake may form on the organic residues and
prevent sufficient heat penetration to kill the
microbes. Experience in the industry has
shown that steam is not amenable to contin-
uous sanitizing of conveyors. Condensation
from this operation and other steam applica-
tions has complicated cleaning operations.
Hot Water
Immersion of small components (i.e.,
knives, small parts, eating utensils, and small
containers) into water heated to 80°C or
higher is another thermal method of sterili-
zation. The microbicidal action is thought to
be the denaturation of some of the protein
molecules in the cell. Pouring “hot” water
into the containers is not a reliable sterilizing
method because of the difficulty of main-
taining a water temperature high enough to
ensure adequate sterilization. Hot water is an
effective, nonselective sanitizing method for
food-contact surfaces; however, spores may
survive more than an hour at 100°C. Hot
water is frequently used for plate heat
exchangers and eating utensils.
The temperature of the water determines
the time of exposure needed to ensure steril-
ization. An example of time–temperature
relationships would be combinations
adopted for various plants that utilize 15
minutes of exposure time at 85°C or 20 min-
utes at 80°C. A shorter time requires a higher
temperature. The volume of water and its
flow rate will also influence the time taken by
the components to reach the required tem-
perature. If water hardness exceeds 60 mg/L,
water scale is frequently deposited on sur-
faces being sanitized unless the water is soft-
ened. Hot water is readily available and
nontoxic. Sanitizing can be accomplished
either by pumping the water through assem-
bled equipment or by immersing equipment
in the water.Radiation
Radiation at a wavelength of approxi-
mately 2,500 Å in the form of ultraviolet
light or high-energy cathode or gamma rays
will destroy microorganisms. For example,
ultraviolet light has been used in the form of
low-pressure mercury vapor lamps to destroy
microorganisms in hospitals and homes. UV
activity appears to be pH and temperature
independent and produces no taste or odor
in treated water. It has been found to pro-
duce few, if any, undesirable by-products,
and little or no mutagenic activity or halo-
genated by-products. Ultraviolet light units
are now commonly used in Europe to disin-
fect drinking and food processing waters and
are being installed in the United States. The
effective killing range for microorganisms
through the use of ultraviolet light is short
enough to limit its utility in food operations
even though its activity is independent of pH
and temperature.
There are three different sources of ioniz-
ing radiation available for the treatment of
food products. They are electron beam,
(e-beam), gamma rays, and X-rays. E-beam
radiation has the shortest penetration range