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Monday, September 28, 2015

Resources for Home Food Freezing of Produce

Resources for Home Food Freezing of Produce
Freezing is the easiest, most convenient, and least time-consuming method of preserving foods. Adding these to the frozen bounty of the past fall's harvest makes for tightly packed freezers. You can freeze almost any foods and a list of foods and freezing instructions can be found here: For a table of foods that don't freeze well see:
Freezing to fend off food spoilage
Food spoilage is caused by microorganisms, chemicals, and enzymes. Freezing foods to 0 degrees F. is recommended for best quality.
o   Freezing stops the growth of microorganisms; however, it does not sterilize foods or destroy the organisms that cause spoilage. A few organisms may die, but once thawed to warmer temperatures, these organisms can quickly multiply.
o   Chemical changes affect quality or cause spoilage in frozen foods. One major chemical reaction is oxidation. If air is left in contact with the frozen food oxidation will occur even in the freezer. An example is the oxidation of fats, also called rancidity.
o   Enzymes are naturally present in foods and their activity can lead to the deterioration of food quality. Enzymes present in animal foods, vegetables and fruit promote chemical reactions, such as ripening. Freezing only slows the enzyme activity that takes place in foods. It does not halt these reactions which continue after harvesting. Enzyme activity does not harm frozen meats or fish, but browning can occur in fruits while they are being frozen or thawed.  
Blanching vegetables before freezing inactivates the enzymes. During blanching, the vegetable is exposed to boiling water or steam for a brief period. The vegetable is then rapidly cooled in ice water to prevent cooking. Following the recommended times for blanching each vegetable is important. Over-blanching results in a cooked product and loss of flavor, color, and nutrients. Under-blanching stimulates enzyme activity and is worse than no blanching at all.  
Chemical Treatment of Fruits
Fruits may also be steamed or cooked before freezing, but are more commonly treated with ascorbic acid to inactivate enzymes responsible for browning. See freezing recommendations for individual foods for specific recommended ascorbic acid usage: and for more information.
Packing and Packaging
Packing methods include dry packs, syrup packs, sugar packs, or possibly crushed or cooked packs. Each has advantages and disadvantages. Pectin or artificial sweeteners are offered as options for specific fruits. See freezing recommendations for individual foods for specific recommended packs: or or for more information.
Good packaging will help prevent air from entering the container and moisture loss. Severe moisture loss, or ice crystals evaporating from the surface of a product, produces freezer burn -- a grainy, brownish or white surface where the tissues have become dry and tough. Freezer-burned food is likely to develop off flavors, but it will not cause illness. Packaging in air-tight rigid containers or heavyweight, moisture-resistant wrap will prevent freezer burn. See: for more specifics.
Safe Defrosting
Never defrost foods on the kitchen counter, in a garage, basement, car, dishwasher or outdoors. These methods can leave your foods unsafe to eat. There are three safe ways to defrost food: in the refrigerator at 40 degrees Fahrenheit or lower, in the microwave immediately before cooking, or in running cold water for very short periods of time. Foods thawed in the microwave or by the running cold water method should be cooked thoroughly immediately after thawing occurs. 
Using and Cooking Frozen Foods
Frozen fruits are often eaten without cooking. Many are best if eaten while they still contain a few ice crystals. Vegetables may be cooked after thawing or while still frozen. Raw or cooked meat, poultry or casseroles can be cooked or reheated from the frozen state. However, it will take approximately one and a half times the usual cooking time for food that has been thawed. Always cook foods to the recommended internal temperature using a food thermometer.

The original version of this page written by Brian A. Nummer, Ph.D., National Center for Home Food Preservation, 2004. Revised November 2012 by Elizabeth L. Andress, Ph.D. and Kasey Christian, M.Ed.


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