Freezing at 0 °F is known to keep food safe by causing microbes to be dormant and prevention of microorganism growth. However, home freezing cannot be trusted to destroy parasites such as trichina and there are reports of food contamination from frozen products such as ice cream which had previous pathogen contamination.
Food stored constantly at 0 °F or below will always be safe. Only the
quality suffers with lengthy freezer storage. Freezing keeps food safe by
slowing the movement of molecules, causing microbes to enter a dormant
stage. Freezing preserves food for extended periods because it prevents
the growth of microorganisms that cause both food spoilage and
Foods if stored frozen constantly at 0 °F will stay safe over longer duration of time (i.e. until the defined time it stays frozen) but quality of the food may reduce over time due to the slow deterioration of the food components.
The storage time mentioned by the US Department of Agriculture is not viewed by the food industry as "indefinite" since the quality of food will also be considered when determining the storage duration.
Although freezing can keep food safe for a very long period, the food industry will not label the storage time of frozen food as indefinite. The quality of food also needs to be considered when determining the storage duration. The storage duration for frozen food (usually in terms of months or years) is usually set out as a quality indicator. The duration may be reduced if the freezer temperature cannot reach -18°C or fluctuates to above -18°C.
- Thawing is a important factor in ensuring safety of frozen foods. Ice cream is an example of a frozen product which is documented to be contaminated by different bacterial pathogens.
Although the growth of microorganisms is inhibited when frozen, they may not be killed and may become active again when food is thawed. Therefore, food should not be thawed at room temperature because the process will take a long time and microorganisms, including pathogens, can multiply before the food is entirely defrosted. This may render frozen cooked food or frozen ready-to-eat food unsafe and increase the risk of cross-contamination by frozen raw food.