Refrigeration and Freezing for Food Preservation

Because food is so important to survival, food preservation is one of the oldest technologies used by human beings. There are many different preservation techniques commonly used today, including:

  • Refrigeration and freezing : Canning : Irradiation : Dehydration : Freeze-drying : Salting : Pickling : Pasteurizing : Fermentation : Carbonation : Cheese-making : Chemical preservation
frozen raspberries
A bag of frozen vegetables will last many months
without spoiling.

The basic idea behind all forms of food preservation is either:

  • To slow down or completely stop the activity of disease-causing bacteria
  • To kill the bacteria altogether

I­n certain cases, a preservation technique may also destroy enzymes naturally found in a food that cause it to spoil or discolor quickly. An enzyme is a special protein that acts as a catalyst for a chemical reaction, and enzymes are fairly fragile. By increasing the temperature of food to about 150 degrees Fahrenheit (66 degrees Celsius), enzymes are destroyed.

A food that is sterile contains no bacteria. Unless sterilized and sealed, all food contains bacteria. For example, bacteria naturally living in milk will spoil the milk in two or three hours if the milk is left out on the kitchen counter at room temperature. By putting the milk in the refrigerator you don’t eliminate the bacteria already there, but you do slow down the bacteria enough that the milk will stay fresh for a week or two.

Refrigeration and Freezing

Refrigeration and freezing are probably the most popular forms of food preservation in use today. In the case of refrigeration, the idea is to slow bacterial action to a crawl so that it takes food much longer (perhaps a week or two, rather than half a day) to spoil. In the case of freezing, the idea is to stop bacterial action altogether. Frozen bacteria are completely inactive.

Refrigeration and freezing are used on almost all foods: meats, fruits, vegetables, beverages, etc. In general, refrigeration has no effect on a food’s taste or texture. Freezing has no effect on the taste or texture of most meats, has minimal effects on vegetables, but often completely changes fruits (which become mushy). Refrigeration’s minimal effects account for its wide popularity.