Freezing is a way to extend the shelf-life of food products using low temperature.    Under freezing temperature, some germs may be killed but some can survive.  However, no germ can grow at such low temperature. 

Before cooking or eating frozen foods, defrosting is required.  Defrosting is a way to soften frozen food into its original form.  During defrosting, a good practice need to be applied.  Otherwise, the germs in food may grow rapidly. 

Four commonly used defrosting methods will be compared.  They are (i) defrosting by refrigerator; (ii) defrosting under running water; (iii) defrosting by microwave oven; and (iv) defrosting at room temperature.  Among these defrosting methods, which is the best way to prepare frozen food?  Check these out! 

Four packs of prepackaged ready-to-eat (RTE) meat product, 2 lb per each pack, are defrosted with package under different conditions.  All those RTE Japanese sesame octopus will be consumed without further heat treatment.  Which method is the fastest and which is the safest way?

  Defrosting by refrigerator (4 C) Defrosting under running water (18 C) Defrosting by microwave oven Defrosting at room temperature (20-25 C)

How fast to defrost

More than 10 hours;

Longest time is needed due to low temperature in the refrigerator (

Around 2 hour;

Around 30 mins;

The fastest way for defrosting among these methods.

5-6 hours;


* *** ****Win **


(kept at the same situation)

1-2 days;

The bacterial growth is low due to low temperature.

< 4 hours;

Bacterial growth can occur. The shelf-life of it depends on the temperature of tap water. Generally, the quality of food is acceptable within 4 hours.

0 hour;

The defrosted food must be eaten immediately because the temperature of defrosted food may rise to 25-35 C which the bacteria can grow rapidly.

0 hours;

All foods should not be placed at room temperature for more than 4 hours. The RTE octopus has been placed at room temperature for 5-6 hours. They may not be safe for consumption.

****Win *** *  

After defrosting, the products are placed at room temperature for 2 hours more. Are they safe for consumption?

During the whole defrosting, the food is kept at low temperature and the germs can not grow rapidly. If they are placed at room temperature for 2 more hours, it is still safe for consumption.

After defrosting, it should be safe for eating after 2 hours display.

After defrosting, the temperature of some parts may rise to >30 C. This can facilitate the bacterial growth. Therefore, they must be eaten immediately. No further display is allowed.

They have already been placed at room temperature for defrosting for 5-6 hours. They may not be safe for consumption.

****Win *** *  






After three rounds of competition, the winners are the ways done by refrigerator and running water. Although the fastest way is to defrost by microwave oven, the safest way is to defrost by refrigerator. In fact, most food manufacturers choose refrigeration to thaw their foods, either cooked or uncooked. This is because the food is kept at low temperature and this can effectively slow down bacterial growth.

Among the above four defrosting methods, defrosting at room temperature is not recommended. We should avoid doing so. This is because the frozen food is placed at ambient temperature for a long time. Time for defrosting highly depends on the quantity needed to be defrosted. In some cases, more than 4 hours may be needed and it is not recommended. For the other three methods, we should pay attention on the following points.

Defrosting by refrigerator

Defrosting under running water

Defrosting by microwave oven

To prevent bacterial food poisoning, don't re-freeze defrosted food.