
raised enough to compensate for the increased resist-
ance. In several cases, the deposit can effectively
reduce the cross-sectional area available to flow.
Thus, not only is product temperature affected, but
so is residence time. Second, flakes of fouled material
can break off from the wall of the heat exchanger and
be carried and deposited elsewhere by the product
flow (i.e., homogenizing values, product packages,
etc.). Finally, the burnt material can give off undesir-
able flavors to the product.
0030 Direct systems are not as susceptible to fouling,
though fouled material may be deposited in the hold-
ing tube, and sometimes in the vacuum chamber.
Temperature Sensing and Utilities
0031 Temperature sensors are installed at appropriate
locations in the product flow stream for controlling
and/or recording temperatures to insure sterilization
of all contact surfaces. During equipment steriliza-
tion, hot water under pressure is circulated through
the processing system and interconnecting piping
with the aseptic filler.
0032 The sterilization temperature is monitored at the
coldest point in the system that must be sterilized.
This point is usually in the return line from the filler.
0033 The proper temperature in the holding section is
very important in achieving the commercial sterility
of a product. It is important that this temperature be
closely controlled, monitored, and recorded.
0034 Steam requirements for aseptic systems vary with
the type of system being used. Steam supply must be
of the proper pressure and flow rate to satisfy process
needs. Product heating and steam seals make up the
two major uses of steam in UHT processing. Steam
that comes in contact with product must be culinary
(food-grade).
0035 Steam seals provide a safety barrier at fittings,
valves, and other locations on the sterile side of
the system. They protect against microbiological
contamination from the environment. The seal as-
sembly provides a steam channel between two
gaskets, allowing live steam to enter and fill the
groove, thus forming a microbial barrier. These seals
are located on the potential problem areas of UHT
systems. Usually they are found in low-pressure areas
(i.e., vacuum chambers) and around moving system
components.
0036 Compressed air is used in pneumatic systems such
as controllers, recorders, valves, and sensors. Manu-
facturers of processing and pneumatic systems specify
compressed-air requirements for their equipment.
Because processing plants have existing air supply
systems, it must be determined whether sufficient air
volume and pressure are available. If not, corrective
procedures should be implemented. Pneumatic
systems are very susceptible to entrained particles of
moisture, oil, or dirt. Proper filtering devices should,
therefore, be installed so specifications for particu-
lates can be adhered to. A pneumatic system jammed
by dirt or oil can cause expensive and frustrating
shutdown of equipment.
0037Compressed sterile air or inert gas is also used by
manufacturers to maintain positive pressure in
aseptic tanks. This positive pressure serves two pur-
poses. First, it acts as a barrier to contamination.
Should there be a crack or failure in the tank or
valves, the positive pressure would blow sterile air
out of the tank, tending to prevent entrance of micro-
organisms. Second, the pressure is used to push the
product from the aseptic tank to the filler.
0038Since the air is in contact with sterile product, it
must also be sterile. Air is sterilized by using filters
and/or heaters. Air, to be sterilized, must itself be of
good quality so removal of moisture, oil, and particu-
lates is essential. The filters used have filter pores of a
size smaller than microorganisms, thus preventing
their passage through the filter. In addition, an air-
sterilizing assembly consisting of a heater, holding
tube, and cooler can be used to sterilize the air.
0039Safeguards must be developed to insure that prod-
uct is rejected if all conditions for sterile-aseptic pro-
cessing are not achieved. These conditions include
maintenance of scheduled process time and tempera-
ture, correct functioning of steam seal and/or sterile
air pressurization systems, or sufficient product pres-
sure downstream from the sterilizer to eliminate any
possibility of sterile product contamination. All im-
portant and necessary aspects of UHT processes must
be documented, with proper records maintained to
demonstrate safe operation.
0040The following sections will examine kinetic aspects
of product processing, including quality retention,
microbial destruction, and aseptic packaging.
See also: Canning: Principles; Cleaning Procedures in
the Factory: Overall Approach; Clostridium: Botulism;
Packaging: Packaging of Solids; Aseptic Filling;
Pasteurization: Principles; Quality Assurance and
Quality Control; Sterilization of Foods
Further Reading
Burton H (1988) Ultra-High-Temperature Processing of
Milk and Milk Products. New York: Elsevier Applied
Science.
Kyereme M, Swartzel KR and Farkas BE (1999) New line
intersection procedure for the equivalent point method
of thermal evaluation. Journal of Food Science 6414:
565–570.
Mermelstein NH (ed.) (1997) Continuous multiphase
aseptic processing of foods. Food Technology 51: 43–62.
3038 HEAT TREATMENT/Ultra-high Temperature (UHT) Treatments