Food temperature

Both heating and cooling food can change its susceptibility to microorganisms [microorganisms: microscopic (too small to see) organisms such as bacteria and viruses ], and therefore its ability to stay fresh.

Cooling

Keeping foods such as dairy produce, cooked foods and raw food ingredients in a refrigerator at a temperature from 0°C to 3°C will slow the growth of microorganisms such as bacteria, but won't stop it entirely.

Freezing

Storing food in a freezer makes long-term storage possible by making bacteria dormant.

Many different types of food are quickly frozen in factories to maintain high standards of freshness and safety. Products are stored in commercial freezers at between -18°C and -29°C. Home freezers store products at -18°C. Freezing does not kill bacteria, but will keep them dormantdormant: A volcano is classed as dormant when it is temporarily inactive but not fully extinct..

Cook-chilled foods

Cook-chilled foods can be cooked from frozen without defrosting. The downside is that cook-chilled foods have a short lifespan and have to be thoroughly reheated before eating - to at least 72°C - to avoid the risk of food poisoning. Leftovers should be disposed of quickly.

In the factory, the foods are prepared by cooking them to 70°C for two minutes to destroy microorganisms. Food is packaged into portions and blast-chilled. Here the temperature is instantly lowered and stored at 0°C to 4°C.

Ultra Heat Treatment (UHT)

UHT is used for products such as "long-life" milk. The product is heated to a temperature of 132°C to 140°C for one second to destroy all bacteria. Then the food is rapidly cooled.

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