Why freezing preserves food

Allow head space between packed food and closure because most fruits expand during freezing. See page 9 for amount of head space needed. Allow fruit to thaw in the unopened package. Fruits packed in dry sugar thaw faster than those in syrup. Fruits packed without sugar take longer to thaw. Fruit to be served in salads, shortcakes, fruit sauce and fruit cups should be only partially thawed.

Thaw fruits for pies until able to separate. Completely thawed fruit will become soft and may darken upon standing. Apple slices — Select firm, crisp full-flavored apples. Wash, peel and core. Slice medium apples into twelfths, large sizes into sixteenths.

Pack in one of the following ways. Syrup pack — Use 40 percent syrup. Press fruit down in containers and add enough syrup to cover. Sugar pack — To prevent darkening of apples during preparation, slice them into a solution of 2 tablespoons salt to a gallon of water. Hold in this solution not more than 15 to 20 minutes. Cool in cold water and drain.

For pies — Follow directions for sugar pack, omitting sugar. Arrange steamed slices in a pie plate as for a pie. Put the filled plate into a plastic bag and freeze. Remove the solid chunk of slices from the plate as soon as frozen. Wrap it tightly and return to the freezer.

At pie-making time, lay the pie-shaped chunk of slices in your pastry. Put on the sugar and seasonings, top with a crust and bake. Applesauce — Select full-flavored apples. Wash apples, peel if desired, core and slice. To each quart of apple slices add a cup water and cook until tender. Cool and package leaving head space. Apple juice — Place freshly made juice in rigid containers.

Leave head space. Halved — Select firm, ripe, uniformly yellow apricots. Sort, wash, half and pit. Peel and slice if desired. Unpeeled apricots are satisfactory for pies. Then cool in cold water and drain. Sugar pack — Before combining apricots with sugar, treat the fruit as follows to prevent darkening:. Stir until sugar is dissolved. Pack apricots into containers and press down until fruit is covered with juice, leaving head space.

Crushed or puree — Select fully ripe fruit. Peel the apricots. Pit and crush them coarsely. For puree, pit and quarter the apricots. Press through a sieve; or heat to boiling point in just enough water to prevent scorching and then press through a sieve. With each quart 2 pounds of prepared apricots mix with 1 cup sugar.

Select avocados that yield to gentle pressure with rind free from dark blemishes. Peel fruit, cut in half and remove pit. Puree — Mash. Use the ascorbic acid if intended use is in a sweet dish.

Use lemon juice if for Guacamole. Pack into containers, leaving head space page 9. Select firm ripe bananas. Mash thoroughly while adding 1 teaspoon lemon juice per cup of mashed banana.

Pack, leaving head space page 9. Whole — Select full-flavored, ripe berries all about the same size, preferably with tender skins.

Sort, wash and drain. If desired, steam for 1 minute and cool immediately. Preheating in steam tenderizes skin and makes a better flavored product. Syrup pack — Pack berries into containers and cover with cold 40 percent syrup. Unsweetened pack — Tray pack or pack berries into containers, leaving head space. Crushed or puree — Select fully ripened berries. Crush, or press berries through a fine sieve for puree. To 1 quart 2 pounds crushed berries or puree, add 1 to 1c cups sugar, depending on tartness of fruit.

Pack into containers, leaving head space. Syrup pack — Pack berries into containers and cover with cold 40 or 50 percent syrup, depending on the sweetness of the fruit. Turn berries over and over until most of the sugar is dissolved. Fill containers, leaving head space. Unsweetened pack — Pack berries into containers, leaving head space.

Crushed or puree — Prepare for packing in the same way as whole berries. Then crush, or press through a sieve or puree. To each quart 2 pounds of crushed berries or puree add 1 cup sugar. Syrup pack — Pack cherries into containers and cover with cold or percent syrup page 13 , depending on tartness of the cherries.

Mix until sugar is dissolved. Select well-colored, tree-ripened fruit with a sweet flavor. Sort, stem, wash and drain. Remove pits if desired — they tend to give an almond-like flavor to the fruit. Pack cherries into containers. With sour cherries, use half sweet cherries and half sour cherries. Pack as above using 50 percent syrup. Ascorbic acid may be added, but is not as essential as it is for sweet cherries alone.

Whole — Choose firm, deep red berries with glossy skins. Stem and sort. Wash and drain. Unsweetened pack — Tray pack or pack into containers without sugar. Syrup pack — Pack into containers.

Cover with cold 50 percent syrup. Puree — Prepare cranberries as for freezing whole. Add 2 cups water to each quart 1 pound of berries. Cook until skins have popped. Press through a sieve. Add sugar to taste, about 2 cups for each quart 2 pounds of puree.

Choose fully ripe berries if freezing for pie — berries a little underripe for jelly making. Sort, remove stems and blossom ends, and wash. Cover with 50 percent syrup. Leave head space: Seal and freeze.

Sections or slices — Select firm tree-ripened fruit heavy for its size and free from soft spots. Wash and peel. Divide fruit into sections, removing all membranes and seeds. Slice oranges if desired. For grapefruit with many seeds, cut fruit in half, remove seeds and cut or scoop out sections.

Pack fruit into containers. Cover with cold 40 percent syrup made with excess fruit juice and water if more liquid is needed. Juice — Select fruit as directed for sections.

Squeeze juice from fruit, using squeezer that does not press oil from rind. Sweeten, if desired, with 2 tablespoons sugar for each quart of juice, or pack without sugar. Pour juice into containers immediately. To avoid development of off-flavors, pack juice in glass jars. Syrup pack — Select firm-fleshed, well-colored, ripe melons. Cut in half, remove seeds and peel.

Cut melons into slices, cubes or balls. Pack into containers and cover with cold 30 percent syrup. Unsweetened pack — Select and prepare as for syrup pack. Place in freezer bag. Serve before completely thawed. Halves, quarters or slices — Choose fully ripe, well-colored, firm nectarines. Overripe fruit may take on a disagreeable flavor in frozen storage. Press fruit down and add syrup to cover, leaving head space. Halves and slices — Peaches in halves and slices have better quality when packed in syrup or with sugar, but a water pack will serve if sweetening is not desired.

Sort, wash, pit and peel. For a better product, peel peaches without a boiling-water dip. Slice if desired. To retard darkening, sprinkle ascorbic acid dissolved in water over the peaches before adding sugar. Water pack — Pack peaches into containers and cover with cold water containing 1 teaspoon crystalline ascorbic acid to each quart of water.

The riper the fruit, the less scalding needed. Cool in cold water, remove skins and pit. To puree, press through a sieve, or heat pitted peaches 4 minutes in enough water to prevent scorching and press through a sieve. With each quart 2 pounds of pureed peaches mix 1 cup sugar.

For better quality, add 1c teaspoons crystalline ascorbic acid to each quart of fruit. Halves or quarters — Select pears that are well ripened and firm, but not hard. Wash fruit in cold water. Peel, cut in halves or quarters and remove cores. Heat pears in boiling 40 percent syrup for 1 to 2 minutes, depending on size of pieces. Drain and cool. Pack pears into containers and cover with cold syrup. Select firm, ripe pineapples with full flavor and aroma.

Pare and remove core and eyes. Slice, dice, crush, or cut the pineapple into wedges or sticks. Unsweetened pack — Pack fruit tightly into containers without sugar.

Syrup pack — Pack fruit tightly into containers. Cover with 30 percent syrup made with pineapple juice, if available, or with water. Whole, halves or quarters — Choose firm tree-ripened fruit of deep color. Sort and wash. Leave whole or cut in halves or quarters. Unsweetened pack — Pack whole fruit into containers, leaving head space. To serve uncooked, dip frozen fruit in cold water for 5 to 10 seconds, remove skins, and cover with 40 percent syrup to thaw. Syrup pack — Pack cut fruit into containers.

Cover fruit with cold 40 or 50 percent syrup, depending on tartness of fruit. Whole — Select fully ripe, juicy berries. Sort, wash carefully in cold water and drain thoroughly. Put into containers, leaving head space. Syrup pack — Put berries into containers and cover with cold 40 percent syrup, leaving head space.

Unsweetened pack — Put berries into containers, leaving head space. Crushed or puree — Prepare as for whole raspberries then crush or press through a sieve for puree.

Stalks or pieces — Choose firm, tender, well-colored stalks with good flavor and few fibers. Wash, trim and cut into 1 or 2 inch pieces or in lengths to fit the package. Heating rhubarb in boiling water for 1 minute and cooling promptly in cold water helps retain color and flavor. Unsweetened pack — Tray pack or pack either raw or preheated rhubarb tightly into containers without sugar. Syrup pack — Pack either raw or preheated and cooled rhubarb tightly into containers, cover with cold 40 percent syrup.

Pack, leaving head space. Whole — Choose firm, ripe, red berries preferably with a slightly tart flavor. Large berries are better sliced or crushed. Sort berries, wash them in cold water, drain well and remove hulls. Syrup packed — Put berries into containers and cover with cold 50 percent syrup, leave head space.

Unsweetened pack — Tray pack or pack into containers, leaving head space. For better color, cover with water containing 1 teaspoon crystalline ascorbic acid to each quart of water.

Sliced or crushed — Prepare for packing as for whole strawberries, then slice, or crush partially or completely. Puree — Prepare strawberries as for freezing whole. Then press berries through a sieve.

To 1 quart 2 pounds puree add b cup sugar and mix well. For success use only high-quality foods and ingredients that freeze well. If you are uncertain about how a prepared food freezes, try freezing a small portion to see if the quality is acceptable. Freezer bags or containers may be used for freezing ground meats, stew meats or other meats frozen into small portions.

Meats can be wrapped using either the drugstore or the butcher wrap see pages The drugstore wrap is preferred, except for irregular meat cuts. The butcher wrap is more appropriate for these. For extra protection against rancidity, obtain a commercial antioxidant from a locker plant or a drugstore. Use it according to the manufacturers directions or add fresh hydrogenated vegetable fat to the rendered lard using this proportion: 2 to 3 pounds of vegetable fat to 50 pounds lard.

Mix thoroughly while still hot. Pour into small containers, filling to the top. The wrap needs to be large enough to fold over the top for sealing.

Chill home-slaughtered poultry in the refrigerator below 40 F, 6 hours for broiler-fryers and 24 hours for older birds. If refrigerator space is not available it can be chilled for two to three hours in a large tub of ice water. Wrap giblets separately from bird. Arrange poultry to give a compact, flat package. Tie the wings and legs closely to the body on birds frozen whole. Poultry may be wrapped in freezer wrap or placed in freezer bags. Remove as much air as possible.

Plastic freezer bags conform to the irregular shape of poultry. A good way to remove air is to place the bird in the bag and then plunge the bag in a pan of cold water. This forces air to the top.

Quickly twist the top in a goose neck and secure. Dry bag thoroughly. Warning: Do not stuff birds before freezing. The time the stuffing takes to cool in the bird before freezing and to thaw and reheat it may be long enough to permit growth of food spoilage and food poisoning bacteria.

Sometimes the meat around bones of young fryers or broilers looks pink or raw even though thoroughly cooked. This color is thought to come from hemoglobin in the bones of young birds. It usually shows up more with long, slow cooking or in chicken that has been frozen. The meat is safe to eat. Bones in cooked chicken sometimes become a dark maroon color. This color usually shows up more in frozen chicken and is due to hemoglobin.

It does not affect the safety of the chicken. Improperly frozen fish develops a bad taste and becomes dry and tough. A number of alternative methods are available for freezing fish properly.

Clean fish as for immediate use. Wash thoroughly. If slime is a problem, rinse fish in a solution of one teaspoon vinegar to three quarts of cold water. Fish are categorized as either fat or lean. Fat fish include mullet, mackerel, trout, tuna, salmon and whitefish. Lean fish include flounder, cod, whiting, snapper and most freshwater fish. Pretreating before freezing improves the quality of fish stored for more than four to six months.

Place fat fish in an ascorbic acid dip for 20 seconds 2 tablespoons ascorbic acid to 1 quart cold water to decrease rancidity and flavor change.

Wrap and freeze immediately. This treatment firms the fish and reduces drip loss when thawed. One of the best methods is to wrap fish with a cling plastic wrap and then overwrap with a freezer wrap.

Squeeze out as much air as possible. Fish may be placed in freezer bags. Submerge the bag in a pan of cold water to force the air out. Do not let water flow into the bag. Seal the bag by twisting and a goose neck. Ice - Freeze unwrapped fish. Then dip frozen fish in near-freezing ice water and return to freezer. Be careful not to break the glaze when handling the fish.

Wrap glazed fish for storage. Dip the fish into the glaze and drain it for several seconds. The glaze will be enough for about a dozen medium-size fillets. Wrap glazed fish and freeze. Place fish in a container and cover with water. Too much water and large containers will draw out nutrients, cause fish to freeze slowly, and cause a soft texture in the fish because of pressure from the ice.

You should freeze fish first and then add cold water and freeze again. This hastens freezing and reduces pressure on the fish flesh. Smoked fish may be refrigerated for two to three weeks. Do not store smoked fish in airtight containers in the refrigerator. For longer storage, the fish may be frozen immediately after smoking.

Use within three months. Use within a few days after thawing. Shrimp can be frozen, cooked or raw, with shells on or off. For maximum storage life and quality freeze shrimp raw with head and dark vein removed, but shells still on.

Shrimp may be placed in a shallow pan, covered with water, frozen and wrapped. Oysters should be fresh and live. Drain, package and freeze. Frozen meats, poultry and fish are best when thawed in the refrigerator in their original wrapping on the lowest shelf in a container.

For faster thawing, place the meat or fish in a waterproof wrapping in cold water. Change the water as needed so it stays cold. You can thaw these foods in a microwave oven. For best quality, cook thawed meat and fish immediately. You can cook meat, poultry and fish from the frozen state, but you must allow additional cooking time.

The amount of additional time depends on the size and shape of the product. Small pieces of frozen fish may take twice as long to cook as fresh or thawed. When you plan to bread and fry frozen meat, poultry or fish, they should be at least partially thawed first for easier handling.

All poultry to be stuffed should be thawed completely for safety. Butter - Freeze only high-quality butter made from pasteurized cream. Over-wrap store wrap with freezer wrapping. Unsalted butter loses flavor so its storage time is shorter. During the defrosting period, the food thaws slightly allowing ice crystals to grow and rupture more cells when they refreeze. Opening the freezer door also allows heat to enter the freezer and repeat this freeze thaw cycle. A chest type freezer may be better in reducing heat loss from opening the door because warm air rises.

Evaporation occurs during the freeze-thaw cycle resulting in dehydration of the product. It is often more noticeable on meats because they are frequently inadequately wrapped.

Freezer burn occurs when frozen food is damaged by crystal growth and dehydration exposing the food to oxygen. Oxygen has a bleaching effect on the food. Freezer burn produces a loss of texture, color, flavor, and aroma. Surface discoloration occurs when enzymes in foods are exposed to the oxygen in air.

These enzymes are inactivated in most vegetables by blanching the raw vegetable in boiling water or in steam for a specified amount of time. Blanching also softens the food making it easier to package and destroys some microorganisms. Completely cool blanched foods before packing and putting in the freezer. The enzymes in foods that are cooked before freezing such as pumpkin puree or applesauce are destroyed in the cooking process.

Sugar may be added as a syrup, or sprinkled on the fruit drawing out the natural juices of the fruit. Freezing fruit in fruit juice containing ascorbic acid will help to control color loss but will not have the benefit of texture control found in sugar syrups.

Penn State Extension's Let's Preserve series provides specific guidelines for freezing a variety of fruits and vegetables. Let's Stay Connected. By entering your email, you consent to receive communications from Penn State Extension.

View our privacy policy. Thank you for your submission! Home Understanding the Process of Freezing. Storing frozen foods at temperatures higher than 0 degrees Fahrenheit 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 materials will prevent freezer burn. Foods for the freezer should be packed properly 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 freezer 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. 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. 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. CFAES provides research and related educational programs to clientele on a nondiscriminatory basis. For more information, visit cfaesdiversity.