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Freezing foods

by: Val Hillers, Ph.D. , Extension Food Specialist


Freezing stops the growth of spoilage organisms but may not kill them. Once frozen foods thaw, surviving organisms will grow even more rapidly than on fresh food.

Foods to be frozen must be packaged in a way that protects them from the dry climate in the freezer. Select packaging materials that are designed for freezer storage.

The quality of frozen fruits and vegetables is greatly improved by a fast freezing rate.  The size and temperature of the freezer and the amount of food placed in the freezer in a single day determines how fast the food will be frozen.

Frozen fruits may be packed in syrup, in dry sugar, or left unsweetened.  The type of pack used will depend on the intended use of the fruit.  Most frozen fruits have better texture and flavor if packed in sugar or syrup.  In all packs except dry unsweetened, liquid should completely cover the fruit to prevent deterioration of top pieces.

Sugar substitutes can be used for people on special diets.  Artificial sweeteners give a sweet flavor but do not furnish the beneficial effects of sugar, like color protection and holding shape.  Fruits preserved with artificial sweeteners will freeze harder and thaw more slowly than those preserved with sugar.  Some artificial sweeteners lose their sweetness or become bitter over time in frozen foods.  Such sweeteners should be added just before serving thawed fruits.

Preventing Discoloration: Some fruits, such as peaches, apples, pears, and apricots, darken quickly when exposed to air and during freezing.  They may also lose flavor when thawed.  The cut surface of the fruit contains enzymes, which, when exposed to air, cause browning.  Listed below are several ways to prevent darkening of fruit.  It is also imperative to prepare only small quantities of fruit at a time if freezing a fruit that darkens rapidly.

Ascorbic acid (vitamin C): Effective in preventing discoloration in most fruits.  It adds nutritive value as well.  Ascorbic acid in table, crystalline, and powdered form is available at many drugstores or where freezing supplies are sold.  Tablets should be crushed so they will dissolve more easily.  A solution suitable for submerging fruit can be made by adding 3 grams (six 500 mg vitamin C tablets) per gallon of water.  Soak fruit in this solution for two minutes to prevent discoloration.

Ascorbic acid mixtures: Special antidarkening preparations made of ascorbic acid mixed with sugar or with sugar and citric acid are on the market. Follow the directions on the package.

Blanching: With the exception of green peppers and onions, vegetables maintain better quality during freezer storage if they are blanched (heated enough to destroy enzymes) before freezing. Vegetables are blanched to slow or stop the action of enzymes that can cause loss of flavor, color, texture, and nutrients.  Blanching also softens vegetables and makes them easier to package. As soon as blanching is complete, vegetables should be cooled quickly in ice water.

Storage Time: To maximize the length of time that frozen foods will maintain good quality, use packaging designed for freezer storage and wrap foods carefully, excluding as much air as possible.  Keep the temperature of the freezer at 0F or below.

Several factors affect the shelf life of frozen meats, fish, and poultry. Generally, fatty meats and fish, cured meats, and shellfish will retain their quality for three months in a 0F freezer.  Lean meats, fish, and poultry can usually be kept up to a year without an appreciable quality loss. These storage times do not indicate that the food is becoming unsafe to eat; instead, they are a measure of time when flavors become strong or fade, textures may worsen, colors may change, and nutritional values decline.

If The Freezer Goes Off

If the power fails or a mechanical failure occurs, certain precautions should be taken to assure the safety of frozen foods.  If service cannot be restored, or the unit repaired in two days:
  1. Do not open the freezer.  Opening the door will hasten thawing of foods.

  2. Cover the freezer with blankets.  Pin the blanket away from the air vents since air is needed when the electricity comes on.

If service is not resumed or the unit repaired within two days, use 2 1/2 pounds of dry ice per cubic foot capacity of the freezer to prevent deterioration or spoilage of frozen foods.  Using gloves, place dry ice on boards or heavy cardboard ON TOP of the packages and do not open the freezer again unless necessary.  This quantity of dry ice should hold the freezer temperature below freezing for two to three days in a freezer with less than half a load and three to four days in a loaded freezer.

Refreezing foods that have thawed:Refreezing will not pose a hazard if the food still contains ice crystals and is not warmer than 40F. There is a quality loss with thawing and refreezing.  This loss is least evident in red meats and most evident in fish and seafood.



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