REPUBLIC OF CAMEROON
Peace – work – Fatherland
REPUBLIQUE DU CAMEROUN
Paix – Travail - Patrie
THE UNIVERSITY OF BAMENDA
UNIVERSITE DE BAMENDA
P.O. Box 39, Bambili, Mezam Division, NW Region, Cameroon
Tel.: (237) 683 79 86 43 - Fax (237) 233 366 030, Website: www.uniba.cm
THE COLLEGE OF TECHNOLOGY (COLTECH) ECOLE DE TECHNOLOGIE
Building Capacities in Innovative Technology for sustainable Development
DEPARTMENT OF NUTRITION FOOD AND BIORESOURCE
TECHNOLOGY
Course Title: FOOD PROCESSING AND PRESERVATION TECHNOLOGY
FREEZING AND THAWING EXPOSE
PRESENTED BY Group 8:
AFUNGFERGERH JULIETTE AYUNIFOR
UBa19P0076
ASONDO FALONE DOROTHY
UBa19P0081
MBAKU KAINA ABON
UBa19P0091
ROASHNEL INJOH
UBa19P0110
API PRECIOUS
UBa19P0080
ACADEMIC YEAR: 2020/2021
FREEZING AND THAWING
In general, frozen foods have an excellent safety record-it is extremely rare for a
foodborne illness to be traced back to a frozen food. Freezing preserves food by stopping
microbes (bacteria, fungi etc.) from multiplying or halting the foods own enzyme activity that
would otherwise cause the food to rot. The way in which freezing preserves food is that, at
freezer temperature most pathogens don’t multiply and many of them perish because their
enzymes don’t work properly to maintain normal cell activity. Also, pathogens need water to
grow and freezing turns the available water into solid ice crystals. The slower the freezing
process the larger the crystals become and the more cells they damage. How quickly the food
freezes depend on the amount of solutes (soluble salts, proteins, and carbohydrates) which affect
the temperature at which ice crystals are formed. The higher the level of solutes the lower the
temperature must be for the food to freeze. When we freeze food in order for us to use this food
for cooking it has to be defrosted through a process called thawing and for defrosting to be done
safely, we have to keep the temperature of the thawing food below 40C. Food should be kept out
of the temperature danger zone (40C to 600C) as much as possible as these are perfect conditions
for pathogens to multiply, release toxins or for spores to germinate.
Freezing:
Freezing, in food processing, is a method of preserving food by lowering the temperature
to inhibit microorganism growth.
The condition of the food at the time of freezing will determine the final quality of the frozen
food. Frozen food can be no better than the food was before it was frozen. Freezing does not
sterilize foods as canning does. It simply retards the growth of microorganisms and slows down
chemical changes that affect quality or cause food spoilage. Almost any food although some food
requires special treatment before they can be frozen safely. If defrosted correctly, frozen food are
generally as their original condition.
In vegetables, some enzymes remain active at freezing temperature and continue to ripen and spoil
them unless stopped with mild cooking (blanching).
Factors affecting quality of Freezing
i.
Enzymes:
Enzyme action can be controlled by freezing, heating and chemical compounds. Freezing
slows enzyme activity so that many frozen foods, such as meats and many fruits, will keep
satisfactorily with little or no further treatment. Enzymes in vegetables are inactivated by heat
during the recommended blanching process. Enzymes in fruits, causing browning and loss of
vitamin C, are controlled by chemical compounds (antioxidants).
ii.
Microorganisms:
Microorganisms do not grow at freezer temperature, but most are not destroyed and will
multiply as quickly as ever when the frozen food is thawed and allowed to stand at
room temperature.
iii.
Freezer Temperature:
A temperature of 0 degrees Fahrenheit or less must be maintained to keep frozen foods at
top quality. The storage life of foods is shortened as the temperature rises. For example, the same
loss of quality in frozen beans stored at 0 F for one year will occur in three months at 10 F, in
three weeks at 20 F, and in five days at 30 F. Fluctuating temperatures result in growth in the
size of ice crystals, further damaging cells and creating a mushier product. Changes in
temperature can also cause water to migrate from the product.
Packaging Materials for Freezing
The prime purpose of packaging is to keep food from drying out and to preserve nutritive value,
flavor, texture and color. Labels on packages will say if the product is suitable for freezer
storage. A good packaging material should have the following characteristics:
• Moisture/vapor-proof or at least moisture resistant.
• Made of food grade material, i.e. designed to be used for food products.
• Durable and leak proof.
• Doesn’t become brittle and crack at low temperatures.
• Resistant to oil, grease or water.
• Protect foods from off flavors and odors.
• Easy to fill and seal.
• Easy to mark and store.
The packaging selected will depend on the type of food to be frozen, personal preference and
availability. For satisfactory results, do not freeze fruits and vegetables
in containers larger than one-half gallon. Packaging not sufficiently moisture/vapor-resistant for
long-time freezer storage includes ordinary waxed paper and paper cartons from cottage cheese,
ice cream and milk. Below is a list of the different packaging materials best suitable for freezing

Rigid containers: they are made of plastic, glass, aluminum and heavily waxed
cardboard and are suitable for all packs. These are often reusable. Straight or tapered
sides on rigid containers make it much easier to remove frozen foods.

Glass jars: they are used for freezing should be made for the purpose. Regular glass jars
may not withstand the extremes in temperature. Do not use regular, narrow-mouth canning
jars for freezing foods packed in liquid. Expansion of the liquid could cause the jar to break
at the neck.

Cans: a few such as shortening and coffee cans, are good for packaging delicate foods.
Line the can with a food-storage bag and seal the lid with freezer tape because they are
not airtight.

Baking dishes: they can be used for freezing, heating and serving. Dishes may be
covered with a heavy aluminum foil taped with freezer tape. To free the baking dish,
wrap the food in casserole-wrap fashion.

Ice cube trays: they are good for freezing foods in small amounts. Freeze food until firm
and then transfer to freezer bags.

Flexible bags or Wrapping: Bags and sheets of moisture vapor-resistant materials and
heavy-duty foil are suitable for dry packed vegetables and fruits, meat, fish or poultry.
Bags can also be used for liquid packs. Protective cardboard cartons may be used to
protect bags and sheets from tearing and to make stacking easier. Laminated papers made
of various combinations of paper,
metal foil, glassine, cellophane and rubber latex are suitable for dry packed vegetables and fruits,
meats, fish and poultry. Laminated papers are also used as protective overwrap.
Packaging, sealing and labelling of freeze food
The freezing of food has to be done in a well-organized manner so the food is well preserved and
remains safe till the period it is to be used for, here are some very good measures that should be
taken note of when preserving food for freezing.

Cool all foods and syrup before packing. This speeds up freezing and helps retain natural
color, flavor and texture of food.

Pack foods in quantities that will be used at one time.

Most foods require head space between the packed food and the closure for expansion as
the food freezes. Loose packing vegetables, such as

asparagus and broccoli, bony pieces of meat, tray-packed foods and breads, do not need
head space.

Pack foods tightly to cut down on the amount of air in the package.

Run a nonmetal utensil, such as a rubber scraper handle, around the inside of the
container to eliminate air pockets.

When wrapping food, press out as much air as possible and mold the wrapping as close to
the food as possible.

When packing food in bags, press the air from the bags. Beginning at the bottom of the
bag, press firmly moving toward the top of the bag to prevent air from re-entering or
force the air out by placing the filled bag in a bowl of cold water taking care that no water
enters the bag. Seal either method by twisting and folding back the top of the bag and
securing with string, good quality rubber band, strip of coated wire or other sealing
device. Many bags may be heat sealed, and some have a tongue-in-groove seal built in.

Keep sealing edges free from moisture or food so a good closure can be made.

When tape is used it should be freezer tape, designed for use in the freezer. The adhesive
remains effective at low temperature.

Label each package with name of product, date, amount and any added ingredients. Use
freezer tape, freezer marking pens or crayons, or gummed labels made especially for
freezer use.
Thawing:
Thawing is the process of taking a frozen food product from frozen to a temperature (usually
above 0C) where there is no residual ice, i.e. defrosting. Thawing is often considered as simply
the reversal of the freezing process. Thawing is primarily used for frozen meats, poultry and
seafood. Most vegetables can be cooked without thawing. It is important to follow these
guidelines to thaw foods safely because bacteria can multiply rapidly when food is left out of the
refrigerator for more than two hours and only one hour, if the temperature is hotter than 90
degrees.
How to Thaw
There are three safe methods to thaw frozen foods:
1. In The Refrigerator:

Plan ahead – most items can take an entire day (or overnight) to thaw.

Place frozen food on a plate, or in a container, to catch any juices that may leak.

Keep the item that’s thawing on the bottom shelf of the refrigerator.

Any food that’s been thawed in the refrigerator can be refrozen, either before or after
cooking.
2. In Cold Water:

This is a faster thawing method compared to thawing in the refrigerator. However, it
could – take a couple of hours depending on weight.

Put the frozen item in a watertight plastic bag or container.

Submerge the item in cold water.

Make sure to change the water every 30 minutes.

Cook immediately after thawed.

You must fully cook all foods thawed with this method, before refreezing them
3. In The Microwave:

Remove any plastic or outer wrapping on the package.

Place in a microwave-safe container and cover.

Follow your microwave instructions to defrost.

Cook immediately after thawing.

You must fully cook all foods thawed in the microwave before refreezing.
However, inherent in thawing is a major problem that does not occur in freezing operation.
The majority of the bacteria that cause spoilage or food poisoning are found on the surfaces of
many foods. During the freezing operation, surface temperatures are reduced rapidly and
bacterial multiplication is severely limited, with bacterial becoming completely dormant below 10C. In the thawing operation these same surface areas are the first to rise in temperature and
bacterial multiplication can recommence. On large objects subjected to long uncontrolled
thawing cycles, surface spoilage can occur before the center regions have fully thawed.