PROCESSING AND PRESERVATION TECHNOLOGIES USED
IN THE FOOD INDUSTRY
Cooling Methods
The Food Code requires that all cooked foods not prepared for immediate service
shall be cooled as quickly as possible to eliminate the possibility of bacteria
development. There are two methods to cool potentially hazardous foods: the twostage method (preferred) and the one-stage method.
The two-stage method reduces the cooked food’s internal temperature in two steps.
The first step is to reduce the temperature from 135ºF to 70ºF within two hours of
preparation and from 70ºF to 41ºF or colder within an additional four-hour period.
Total cooling time should never exceed six hours.
The one-stage method is designed to reduce the cooked food’s internal temperature
from 135ºF to 41ºF or colder within four hours of preparation. This method should
only be used if the food is prepared from ingredients at ambient temperature. When
deciding how best to cool potentially hazardous foods, keep in mind the following
factors:
• The size or amount of food being cooled;
• The density of the food – a broth is less
dense than a casserole;
• The container in which the food is being
stored – shallow pans cool foods faster than
deep pans.
Simply placing a cooked food item in a refrigerator to cool may not be sufficient to
reduce the threat of bacterial growth. In addition, a warm or hot food item placed
into a refrigerator may actually raise the temperature inside the unit and jeopardize
the safety of other stored foods. Once the food item has been properly cooled, it
should be stored properly – covered and labelled with the date the product was
prepared.
Freezing
Freezing food preserves it from the time it is prepared to the time it is eaten. Freezing
food slows down decomposition by turning residual moisture into ice, inhibiting the
growth of most bacterial species. In the food commodity industry, there are two
processes: mechanical and cryogenic. However, it is important to preserve the food
quality and texture. Quicker freezing generates smaller ice crystals and maintains
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cellular structure. Cryogenic freezing is the quickest freezing technology available
due to the ultra low liquid nitrogen temperature −196 °C (−320.8 °F)
Quality of frozen foods depends directly on the speed of the freezing, as it has a
direct impact on the size and the number of ice crystals formed within a food
product's cells. Slow freezing leads to fewer but larger ice crystals while fast freezing
leads to smaller but more numerous ice crystals. Large ice crystals can puncture the
walls of the cells of the food product which will cause a degradation of the texture of
the product as well as the loss of its natural juices during thawing. That is why there
will be a qualitative difference observed between food products frozen by ventilated
mechanical freezing, non-ventilated mechanical freezing or cryogenic freezing with
liquid nitrogen.
Pasteurization
It is a process that kills microbes (mainly bacteria)
as milk, juice, canned food, and others.
in food and drink,
such
Pasteurization is an all-natural process, in that it involves only heat (not chemicals or
irradiation). Unlike sterilization, pasteurization is not intended to kill all microorganisms in the food. Instead, it aims to reduce the number of viable pathogens so
they are unlikely to cause disease (assuming the pasteurized product is stored as
indicated and is consumed before its expiration date).
Modern methods usually require that the product is heated to at least 72 °C for at
least 16 seconds,] then cooling it to 4 °C to ensure any harmful bacteria are destroyed.
Sterilization
It is a term referring to any process that eliminates (removes) or kills all forms of life,
including contagious agents such as fungi, bacteria, viruses, spore forms, etc.
Sterilization can be achieved with one or more of the following: heat, chemicals,
irradiation, high pressure and filtration.
Drying food
Foods are dried to inhibit microbial development and quality decay. However, the
extent of drying depends on product end-use. Cereals and oilseeds are dried after
harvest to the moisture content that allows microbial stability during storage.
Vegetables are blanched before drying to avoid rapid darkening, and drying is not
only carried out to inhibit microbial growth, but also to avoid browning during
storage. With dried fruits, the reduction of moisture acts in combination with its acid
and sugar contents to provide protection against microbial growth. Products such as
milk powder must be dried to very low moisture contents in order to ensure
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flowability and avoid caking. Other products as crackers are dried beyond the
microbial growth threshold to confer a crispy texture, which is liked by consumers.
Vacuum packing
Vacuum packing is a method of packaging that removes air from the package prior
to sealing. This method involves (manually or automatically) placing items in a
plastic package, removing air from inside, and sealing the package. The intent of
vacuum packing is usually to remove oxygen from the container to extend the shelf
life of foods and, with flexible package forms, to reduce the volume of the contents
and package. Vacuum packing reduces atmospheric oxygen, limiting the growth of
aerobic bacteria or fungi, and preventing the evaporation of volatile components. It is
also commonly used to store dry foods over a long period of time, such as cereals,
nuts, cured meats, cheese, smoked fish, coffee... On a more short term basis, vacuum
packing can also be used to store fresh foods, such as vegetables, meats, and liquids,
because it inhibits bacterial growth.
For delicate food items which might be
crushed by the vacuum packing process
(such as potato chips), an alternative is to
replace the interior gas with nitrogen.
This has the same effect of inhibiting
deterioration due to the removal of
oxygen.
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PRACTICE
a) Answer the questions.
1. Name 3 most important factors which affect cooling the foods.
________________________________________________________________________
2. Explain the main difference between the slow and fast freezing process.
________________________________________________________________________
3. Describe the difference between pasteurization and sterilization.
________________________________________________________________________
4. Describe the procedure of vacuum packing.
________________________________________________________________________
b) Match the words and the explanations.
1. the two-stage cooling method
___ generates smaller and more ice
crystals.
2. quicker freezing
___ depends on product end-use.
3. The extend of drying
___ reduces the foods inner temperature
in two steps.
4. vacuum packing
___ applies a precise amount of heat for a
specific period of time.
___ prevents the evaporation of volatile
components.
Viri:
http://www.profoodsafety.org/images/english/English%20Cooling%20Methods%20fact%20sheet.pdf
http://en.wikipedia.org/wiki/Frozen_food
http://en.wikipedia.org/wiki/Pasteurization
http://en.wikipedia.org/wiki/Sterilization_(microbiology)
http://en.wikipedia.org/wiki/Drying_%28food%29
http://en.wikipedia.org/wiki/Vacuum_packing
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