2. Refrigeration, freezing and freeze drying

This involves cooling food to low temperatures to slow down enzyme activity as well as the growth of microorganisms.

Refrigeration is cooling the environment artificially to bring the temperature below ambient temperature, usually ranging from 4 to 10°C. Foods commonly stored using cooling methods are usually highly perishable products, like meat, dairy, and fish, thus increasing their shelf-life.

Freezing means cooling food to temperatures of -18°C for longer storage periods. At temperatures below 0°C the water inside the food forms ice crystals, which means some foods cannot be frozen, because the melting ice will either cause structural breakdown of the food (like lettuce, cucumbers, soft herbs, dairy products, etc.) or be soaked up, leaving the food soogy, like crumb based cakes, etc.

Food type

Recommended freezing time frames (if your freezer runs at -18oC)

Uncooked meat  (roasts, steaks, chops etc)

4-12 months

Uncooked mince meat

3-4 months

Cooked meat

2-3 months

Cured meats (ham & bacon )

1-2 months

Uncooked poultry (chicken, turkey etc)

9-12 months

Cooked poultry

4 months

Fish-raw & cooked

2-4 months

Frozen dinners ( e.g. lasagne, pizza, shepherd’s pie)

3-4 months

Soups, stews and casseroles

2-3 months

Milk

Up to 1 month  

Butter

Up to 3 months

Grated cheese

Up to 4 months

Vegetables

Up to 12 months

Fruit

Up to 6 months

Eggs – either separate the yolk and white, or beat the eggs before freezing

Up to 6 months

Cakes and baked goods without icing

6-8 months

Bread

Up to 3 months

Raw pastry

6 months


Freeze drying is also known as lyophilization. During this process, the moisture in the food is removed (sublimated) under frozen and vacuum conditions, which causes a direct transition of water from its solid (ice) to vapor, omitting the liquid state, and then desorbing the water from the “dry” layer. The process is used for heat-sensitive foods.