Control by Heat (Thermal Processing) ◾ 455
number (~90%) of associative (many of which can cause spoilage) microorganisms (yeasts, molds,
bacteria, and viruses). In certain foods, pasteurization also destroys some natural enzymes (e.g.,
phosphatase in milk). The temperature and time are set to the lowest level to meet the microbiological objectives and to minimize thermal damage of the food, which otherwise could reduce the
acceptance quality (such as heated flavor in milk) or pose processing difficulties (such as coagulation of liquid egg). Depending on the temperature used, thermoduric cells of spoilage bacteria
and spores of pathogenic and spoilage bacteria survive the treatment. Thus, additional methods
need to be used to control the growth of survivors (as well as post-pasteurization contaminants) of
pasteurized products unless a product has a natural safety factor (e.g., low pH in some acid products). Refrigeration, modified atmosphere packaging, incorporation of preservatives, reduction of
A W , and other techniques are used, when possible in combination, to prevent or retard the problem
of microbial growth in low-heat-processed products. Microbial heat-stable enzymes and toxins are
not destroyed unless a food is heated for 30 minutes or longer at or above 90°C (194°F).
Pasteurization of milk has been used for a long time. Two methods, heating at 145°F (62.8°C)
for 30 minutes or 161°F (71.7°C) for 15 seconds, are used to destroy the most heat resistant Q
fever–causing pathogen, Coxiella burnetii. The methods are also designated, respectively, as lowtemperature, long-time (LTLT) and high-temperature, short-time (HTST) methods. As indicated
previously, regulation requires every particle of milk to be heated at 145°F for 30 minutes or at
161°F for 15 seconds (holding time). Foods that are not uniformly heated to the specified temperature and time can be involved in foodborne diseases. Immediately after the holding time, the milk
is cooled to 40°F (4.5°C), packaged, and maintained at that temperature until consumed. Lowheat treatment is used for processing many products by using different times and temperatures, for
example, ice cream mix, 180°F (82.3°C) for 25 seconds or 160°F (71.2°C) for 30 minutes; liquid
whole egg, 140°F (60°C) for 3.5 minutes (intended to destroy Salmonella); fruit juices, 60°C–70°C
(140°F–158°F) for 15 minutes or 80°C–85°C (176°F–185°F) for one minute; wine, 82°C–85°C
(179.6°F–185°F) for one minute; pickles in acid (pH 3.7), 74°C (165.2°F) for 15 minutes; vinegar,
65.6°C–71.1°C for one minute or 60°C for 30 minutes (heating of all low-pH products is designed
to destroy aciduric spoilage microorganisms); crab meat, 70°C (158°F) for 10 minutes; low-heatprocessed meat products, 60°C–70°C (140°F–158°F) internal temperature (depending on the size,
it can take two hours for the center of a product to reach the desired temperature; heating is not
intended to kill Clo. botulinum Type A or nonproteolytic B spores). The time and temperature of
pasteurization for different foods is also specified by regulatory agencies.
In addition to the use of hot water (e.g., for milk) or moist heat (e.g., for meat products) to heat
process some foods, other products, such as dried egg whites and dried coconut, are pasteurized
by dry heat. In such a condition, the products are exposed to 50°C–70°C (122°F–158°F) for five
to seven days.
In the production of some fermented foods, the raw materials are heated to a high temperature to destroy vegetative cells of pathogens and spoilage microorganisms, which include thermoduric bacterial cells. Raw milk used for the production of buttermilk, acidophilus milk, and
yogurt are given a 30- to 60-minute heat treatment at approximately 90°C (194°F) before adding
starter- culture bacteria. Heating helps the starter culture bacteria grow preferentially, in addition
to improving the gelling properties of the milk proteins at low pH.
High-Heat-Processed Foods
This process involves heating foods at or above 100°C (212°F) for a desired period of time. The
temperature and time of heating are selected on the basis of product characteristics and the specific
number (~90%) of associative (many of which can cause spoilage) microorganisms (yeasts, molds,
bacteria, and viruses). In certain foods, pasteurization also destroys some natural enzymes (e.g.,
phosphatase in milk). The temperature and time are set to the lowest level to meet the microbiological objectives and to minimize thermal damage of the food, which otherwise could reduce the
acceptance quality (such as heated flavor in milk) or pose processing difficulties (such as coagulation of liquid egg). Depending on the temperature used, thermoduric cells of spoilage bacteria
and spores of pathogenic and spoilage bacteria survive the treatment. Thus, additional methods
need to be used to control the growth of survivors (as well as post-pasteurization contaminants) of
pasteurized products unless a product has a natural safety factor (e.g., low pH in some acid products). Refrigeration, modified atmosphere packaging, incorporation of preservatives, reduction of
A W , and other techniques are used, when possible in combination, to prevent or retard the problem
of microbial growth in low-heat-processed products. Microbial heat-stable enzymes and toxins are
not destroyed unless a food is heated for 30 minutes or longer at or above 90°C (194°F).
Pasteurization of milk has been used for a long time. Two methods, heating at 145°F (62.8°C)
for 30 minutes or 161°F (71.7°C) for 15 seconds, are used to destroy the most heat resistant Q
fever–causing pathogen, Coxiella burnetii. The methods are also designated, respectively, as lowtemperature, long-time (LTLT) and high-temperature, short-time (HTST) methods. As indicated
previously, regulation requires every particle of milk to be heated at 145°F for 30 minutes or at
161°F for 15 seconds (holding time). Foods that are not uniformly heated to the specified temperature and time can be involved in foodborne diseases. Immediately after the holding time, the milk
is cooled to 40°F (4.5°C), packaged, and maintained at that temperature until consumed. Lowheat treatment is used for processing many products by using different times and temperatures, for
example, ice cream mix, 180°F (82.3°C) for 25 seconds or 160°F (71.2°C) for 30 minutes; liquid
whole egg, 140°F (60°C) for 3.5 minutes (intended to destroy Salmonella); fruit juices, 60°C–70°C
(140°F–158°F) for 15 minutes or 80°C–85°C (176°F–185°F) for one minute; wine, 82°C–85°C
(179.6°F–185°F) for one minute; pickles in acid (pH 3.7), 74°C (165.2°F) for 15 minutes; vinegar,
65.6°C–71.1°C for one minute or 60°C for 30 minutes (heating of all low-pH products is designed
to destroy aciduric spoilage microorganisms); crab meat, 70°C (158°F) for 10 minutes; low-heatprocessed meat products, 60°C–70°C (140°F–158°F) internal temperature (depending on the size,
it can take two hours for the center of a product to reach the desired temperature; heating is not
intended to kill Clo. botulinum Type A or nonproteolytic B spores). The time and temperature of
pasteurization for different foods is also specified by regulatory agencies.
In addition to the use of hot water (e.g., for milk) or moist heat (e.g., for meat products) to heat
process some foods, other products, such as dried egg whites and dried coconut, are pasteurized
by dry heat. In such a condition, the products are exposed to 50°C–70°C (122°F–158°F) for five
to seven days.
In the production of some fermented foods, the raw materials are heated to a high temperature to destroy vegetative cells of pathogens and spoilage microorganisms, which include thermoduric bacterial cells. Raw milk used for the production of buttermilk, acidophilus milk, and
yogurt are given a 30- to 60-minute heat treatment at approximately 90°C (194°F) before adding
starter- culture bacteria. Heating helps the starter culture bacteria grow preferentially, in addition
to improving the gelling properties of the milk proteins at low pH.
High-Heat-Processed Foods
This process involves heating foods at or above 100°C (212°F) for a desired period of time. The
temperature and time of heating are selected on the basis of product characteristics and the specific