Freezing is the easiest, most convenient, and least time- consuming method of preserving foods. Freezing does not sterilize foods or destroy the organisms that cause spoilage; the extreme cold simply slows the growth of microorganisms and the chemical changes that affect quality or cause spoilage.
Enzymes are complex proteins, present in all living tissue, that help organisms ripen and mature. During freezing, enzyme action is slowed but not stopped. If not inactivated, these enzymes can cause color and flavor changes and loss of nutrients during freezer storage.
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. The use of microwave ovens for blanching has become popular. However, microwave blanching produces uneven results because of varied heat patterns within an oven and from one oven to another. Microwave blanching requires working with only small quantities at a time; there is no time saving when working with large quantities of vegetables.
Blanching also helps destroy microorganisms on the surface of the vegetables. When blanched, vegetables such as broccoli and spinach become more compact. Following the recommended times for blanching each vegetable is important. Overblanching results in a cooked product and loss of flavor, color, and nutrients. Underblanching stimulates enzyme activity and is worse than no blanching at all.
Enzymes in fruits can cause browning and loss of Vitamin C. Fruits, however, are not usually blanched. Instead, ascorbic acid (Vitamin C) is used to control enzymes in frozen fruits. Commercial mixtures of ascorbic acid are available for home use. Citric acid or lemon juice also may be used to prevent darkening of fruits, but they are not as effective as ascorbic acid. Packing fruit in sugar or sugar syrup also will control browning.Freezer Storage
To maintain top quality, store frozen fruits and vegetables at 0 degrees Fahrenheit (F) or lower. Storing frozen foods at temperatures higher than 0 degrees F increases the rate of deterioration and shortens the shelf life of foods. Fluctuating freezer temperatures can cause the ice in the foods to thaw slightly and then refreeze. Every time this happens, the smaller ice crystals form larger ones, further damaging cells and creating a mushier product.
Moisture loss, or ice crystals evaporating from the surface of a product, produces freezer burn--a grainy, brownish spot where the tissues become dry and tough. Freezer-burned food is likely to develop off flavors, but it will not cause illness. Packaging in heavyweight, moisture-resistant wrap will prevent freezer burn.Containers for Freezing
Foods for the freezer must have proper packaging materials to protect their flavor, color, moisture content, and nutritive value. Select packaging materials with these characteristics:
Suitable packaging materials include rigid plastic containers with straight sides, glass jars made for freezing and canning, heavy-duty aluminum foil, moisture-vapor resistant bags, and paper.
Containers intended for short-term storage, such as bread wrap; cottage cheese, milk, or ice cream cartons; regular aluminum foil; or waxed paper do not provide effective protection against flavor and moisture loss or freezer burn during long-term storage.
Plastic containers designed for long-term freezer storage may or may not be suitable for direct use in a microwave oven.Packaging Foods
Cool all foods and syrup before packing. Pack foods in quantities that are usable for a single meal.
Pack cold foods tightly into containers. Because most foods expand on freezing, allow ample headspace (space between food and closure). The amount of space needed will vary depending on the food and size of containers. When packing food in bags, press out excess air before sealing. Label and date each package. It is also helpful to list number of servings on the label.
For quick freezing, spread packages among already frozen foods. Leave a small space between packages and add only the amount of unfrozen food to the freezer that will freeze within 24 hours, about 2 to 3 pounds of food to each cubic foot of freezer capacity.Freezing Pointers
What to Do If Your Freezer Stops
Keep the freezer closed. If it looks like the freezer will be stopped for more than 24 hours, use dry ice (if you can get it) or move the food to another freezer.
Thawed fruits that smell and taste good can be refrozen. Thawed fruits can be used in cooking, baking, or making jams and jellies.
Vegetables containing ice crystals or at 40°F or below can be refrozen. Thawed vegetables in good condition can be cooked in soups, stews, or casseroles and then frozen.
Examine meats and poultry for color changes or off odors. Only refreeze packages that still contain ice crystals or are cold to touch (40 degrees F or below). Repackage in moisture- and vapor-proof wrap. Discard any thawed meat or poultry. Ground meat cold to touch should be cooked before refreezing.
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