Thawing

Thawing
Definition
• Thawing is the process of changing the state of a
product from frozen to unfrozen.
• It involves transferring “heat” to a frozen product to
melt the ice that was formed within the product
during the freezing process.
• Like freezing, thawing should be carried out as
quickly as possible to maintain the quality of the
product.
• If the thawing process is carried out correctly there
should be little effect on the quality of the product.
The Temperature Danger Zone
• The Temperature Danger Zone is the range of
temperatures where bacteria grows easily and quickly.
• The Temperature Danger Zone is between 4 -60 deg C.
• Keep cold foods in the refrigerator at 4 deg C or below
or in the freezer at -18 deg C to avoid the
Temperature Danger Zone.
• Keep hot foods at 60 deg C or above to avoid the
Temperature Danger Zone.
• Never use raw meat or poultry if it has set out at
room temperature for more than two hours.
Thawing process
1. Defrosting Food in The Refrigerator
• The safest way to defrost food is in the refrigerator. When

food is defrosted in the refrigerator, the food doesn’t need to
pass through the temperature danger zone. This is why it’s
the safest of all defrosting methods.
• To defrost food in the refrigerator, ensure that the

temperature is 4°C (40°F) or below and that the items being
defrosted are placed on the lowest shelves to prevent
dripping or splashing.
• It can take quite a long time to defrost food in a refrigerator.

Even small items will take at least a full day to defrost.
Thawing process
2. Defrosting Food In The Microwave
• Microwave ovens can be quite useful for defrosting small
items quickly.
• It’s important to remember that heat isn’t distributed

evenly through food when using a microwave, so it will be
necessary to stir the item during the defrosting process.
• Microwave defrosting is only recommended for food items

that are to be cooked immediately after defrosting
Thawing process
3. Defrosting Food as Part of the Cooking Process
• Some food items have been designed to be

cooked from frozen such as hamburger
patties, frozen vegetables and frozen pastry.
• Always follow the manufacturer's instructions

and check the internal temperature of the
food before serving
Thawing process
4. Defrosting Food Under Cold Running Water
• It is the least preferred method of defrosting as it can be

quite easy for the food item to reach temperatures within
the temperature danger zone.
• For this method, use a clean and sanitised sink, and
completely submerge the food item under running potable
water of 20°C or lower. The food should be held in leak-
proof, waterproof packaging.
• The sink must be large enough to allow the food item to be
completely covered, and defrosting must be completed
within 2 hours or less.
• Clean and sanitise the sink after defrosting food in it.
Thawing process
5. At room temperature
• Pastries, breads, and fruits may be thawed for 2-4

hours at room temperature. Do not use this method
for meat, fish, and vegetables.
Cooking Without Thawing
• It is safe to cook foods from the frozen state.
• The cooking will take approximately 50%
longer than the recommended time for fully
thawed or fresh meat and poultry.
Thawing time calculation
• Although freezing and thawing processes have
some similarities in that both involve phase change
processes, there are also a number of differences.
For example, surface boundary conditions during
thawing become complicated due to the formation
and later melting of frost on the surface
• In thawing, an unfrozen layer moves progressively
inward from the food’s outer surfaces toward its
center.
Thawing time calculation
• The equation proposed by Cleland is relatively easy to use
for predicting thawing times:
• where
• dc : characteristic dimension (m)
• Ef : shape factor
• Δ H10 : volumetric enthalpy change from 0°C to
10°C
• Ta : freezing medium temperature (°C)
• TF : initial freezing temperature (°C)
Key points
1. Remember to thaw frozen raw food below ready to eat
food, so that the juices from the thawing food cannot fall
onto the ready to eat food. This is called cross
contamination
2. If you use a microwave , use the food immediately after

thawing. When thawing frozen food, the 2 h/4 h time
temperature and food safety rule may be used.
3. The safest place to thaw frozen food is in the refrigerator or

cool room You will have to plan ahead. Some food can take
as long as one or two days to completely thaw
Key points
4. Food should be covered while thawing, labeled &dated so
plan ahead Food should be completely thawed before
cooking
5. Thawing food out of refrigeration can allow bacteria to

multiply. Food may become contaminated during thawing
6. Keep all food covered, wrapped or in a container while

thawing. Never re-freeze thawed food.
7. Do not use food until it is completely thawed. Throw away

food that has been left to stand at between 5ºC- 6oºC for
more than four hours

Thawing

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Thawing

• The safest way to defrost food is in the refrigerator. When

• To defrost food in the refrigerator, ensure that the

• It can take quite a long time to defrost food in a refrigerator.

• It’s important to remember that heat isn’t distributed

• Microwave defrosting is only recommended for food items

• Some food items have been designed to be

• Always follow the manufacturer's instructions

• It is the least preferred method of defrosting as it can be

• Pastries, breads, and fruits may be thawed for 2-4

2. If you use a microwave , use the food immediately after

3. The safest place to thaw frozen food is in the refrigerator or

5. Thawing food out of refrigeration can allow bacteria to

6. Keep all food covered, wrapped or in a container while

7. Do not use food until it is completely thawed. Throw away

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