Frozen food is food preserved by the process of freezing. Freezing food is a common method of food preservation which slows both food decay and, by turning water to ice, makes it unavailable for bacterial growth and slows down most chemical reactions.
Process
Freezing only slows the deterioration of food and while it may stop the growth of micro-organisms, it does not necessarily kill them. Many enzyme reactions are only slowed by freezing. Therefore it is common to stop enzyme activity before freezing, either by blanching or by adding chemicals.
Foods may be preserved for several months by freezing. Long-term freezing requires a constant temperature of -18 °C (0 degrees Fahrenheit) or less. Some freezers cannot achieve such a low temperature. The time food can be kept in the freezer is reduced considerably if the temperature in a freezer fluctuates. Fluctuations could occur by a small gap in the freezer door or adding a large amount of unfrozen food.
Texture of frozen food
Freezing adversely affects the texture of many foods, and the texture of nearly all foods is damaged by thawing and re-freezing. Since water expands when it freezes, cell walls in food are often ruptured, resulting in food that is limp or pulpy when thawed. This is especially true of fruits and vegetables that have a high water content. Less damage is done to vegetables that are high in starch. Less damage is also done if the food is frozen quickly, so unfrozen food should be placed in the coldest areas, which are near the bottom of the freezer. Some additives, such as sugar or sorbitol, can hinder water’s crystallization and preserve the food’s cellular structure. Defects in the texture of thawed food can sometimes be obscured by cooking.
Some food is frozen specially to get a frozen texture. Ice cream is an example of a food which is intended for consumption while frozen.
Quick-freezing
American inventor Clarence Birdseye (1886-1956), who developed the quick-freezing process of food preservation in the early 20th century, is considered the father of the frozen-food industry.
The food industry uses a technique called flash freezing, an application of supercooling, to quickly freeze food items. In this case, water contained inside the food is subjected to temperatures well below its melting/freezing point (273 K or 0°C). This causes the water inside the foods to freeze very quickly.
Traditional and other use
Many Arctic communities would preserve food in holes or larders dug into the ice. There is a tradition in Scandinavia of preserving fish and especially herrings in this way.
Cold stores provide large-volume, long-term storage for strategic food stocks held in case of national emergency in many countries.
Seeds are stored in freezers at −18 °C or below in seedbanks. The seeds are stored as a source for planting in case seed reserves elsewhere should be destroyed. The seeds stored may be those of food crops or rare species.
See also
- Shelf life
- Recommended times for refrigerator and freezer food storage