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;
|
| * | *** | **** |
** | |
|
Shelf-life (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. |
| **** |
*** | * | ||
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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. |
| **** |
*** | * | ||
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Result |
9* |
9* |
6* |
2* |
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
- We need to plan ahead that what food will be cooked in the next day because of a long defrosting time, usually overnight.
- Food should be wrapped to prevent contamination.
- We should place ready-to-eat (RTE) food and non-ready-to-eat food at upper and lower compartments of refrigerator respectively.
- The defrosted food should be placed in refrigerator at all time until it is used or consumed.
- Food should be used or consumed within 2 days.
Defrosting under running water
- RTE food should be wrapped before putting in water to prevent contamination.
- Non-RTE food could be defrosted without wrapping, but thorough cleaning of equipment and utensil must be performed before and after to avoid transmission of bacteria to other food.
- Water should be kept running to facilitate faster defrosting.
- If the defrosted food is not used immediately, they should be wrapped and put in refrigerator.
Defrosting by microwave oven
- Food should be wrapped before putting in microwave oven.
- The defrosting should be divided into two phases. Food should be taken out for stirring or turning over to facilitate adequate and even defrosting.
- We should turn off the machine and wait for a few seconds before taking food out.
- Food must be cooked or consumed immediately because the temperature of some parts of the food may become higher than 30 C. Such warm temperature may facilitate bacterial growth in food.
To prevent bacterial food poisoning, don't re-freeze defrosted food.