FOOD PRESERVATION Freezing Basics
Author: Barbara Willenberg
Date: 0101-01-01T00:00:00+00:00
Keywords: Food

Information from

FOOD PRESERVATION

Human

Environmental

Freezing

Sciences

Extension

ᮢ

Basics

ᮢ

Barbara J. Willenberg

ᮢ

Department of Food Science and Human Nutrition University of Missouri-Columbia Freezing is one of the easiest and surface, the faster the growth of

Quality for Keeps
least time-consuming methods of spoilage organisms occurs. If you store food preservation. Most foods raw or precooked frozen foods long retain their natural color, flavor and tex-enough at a high enough temperature ture better than when other methods of after thawing, spores of Clostridium food preservation are used. In addition, botulinum can grow and produce toxin.

the kitchen remains cool and comfort-For this reason, we recommend that able during the process.

food be thawed in the refrigerator Disadvantages of freezing include where spoilage organisms will not grow the initial investment for equipment — it as quickly.

costs a great deal to purchase and Chemical changes
maintain a freezer. In addition, the size by spoilage organisms, always keep of the freezer limits the amount of stor-your equipment, work surfaces and during freezing
age space, and the freezing process hands clean. Washing produce thor-Enzymes are proteins present in gives some foods an undesirable tex-oughly before freezing removes garden plants and animals. While the plant or ture.

soil, a source of spoilage organisms.

animal lives, enzymes help speed up Freezing does not destroy Clostridi-the ripening and maturing processes.

Growth of spoilage
um botulinum, the spoilage organism Even after we harvest plants or slaugh-organisms
that causes the greatest problem in ter animals, enzyme reactions can con-Freezing does not destroy spoilage canning low acid foods like vegetables tinue and result in undesirable color, organisms; it merely stops their growth and animal products. However, Clostrid-flavor and texture changes in the food.

temporarily. During the freezing ium botulinum will not grow and pro-Freezing slows down, but does not process, microbial growth can occur duce toxin (poison) at correct freezer destroy, enzymes in fruits and vegeta-under the following circumstances: temperatures (0 degrees F or below).

bles. That is why it is important to stop

■ when freezing does not take place Therefore, freezing is a safe and easy enzyme activity before freezing. The rapidly;
alternative to pressure canning low-two methods you can use are blanch-

■ when freezer temperature is above acid foods.

ing and adding chemical compounds 0 degrees F.

When thawing food, remember that such as ascorbic acid.

Keep the freezer temperature at or freezing did not destroy any spoilage below 0 degrees F to prevent the organisms that might have been pre-Enzymes in vegetables
growth of spoilage organisms and to sent in the food. As the temperature of Enzymes in vegetables are inactivat-minimize changes in flavor, texture and food rises during thawing, growth of ed by blanching. To blanch vegetables, nutritive value of food.

spoilage organisms begins. The faster place them in boiling water or steam for To prevent contamination of all foods the food warms up, especially on the a brief period of time. Next, cool the Published by MU Extension, University of Missouri-Columbia GH 1501ᮣ
vegetables rapidly in ice water (this Rancidity in foods
can be controlled by freezing products prevents further cooking). Although Fats in meat, fish and poultry as quickly as possible. In rapid freez-some publications state that blanching become rancid during freezer storage.

ing, a large number of small ice crys-is unnecessary, it is essential for top-This is caused by contact with air left in tals are formed. These small ice quality, frozen vegetables.

the package or air that enters the pack-crystals cause less damage to cell Blanching also helps to destroy age because proper storage materials walls than slow freezing, which pro-microorganisms on the surface of the were not used. However, even with duces larger ice crystals.

vegetables. It makes vegetables like proper packaging materials, rancidity For best results, freeze foods at 0
broccoli and spinach more compact, will occur over time. Off flavors are the degrees F or lower as soon as they are and as a result, they take up less room result of this chemical change. Control packaged and sealed. Set the tempera-in the freezer. Follow the recommended rancidity by trimming excess fat from ture control at -10 degrees F or lower time (see MU publication GH 1503, meat before freezing, using a wrapping about 24 hours in advance to help food Freezing Vegetables) for blanching each material that prevents air from reaching freeze rapidly. Do not overload your vegetable carefully. Over-blanching the product, and by storing foods for freezer with unfrozen food. Add only results in a cooked product and a loss of the recommended length of time.

the amount that will freeze within 24
flavor, color and nutrients. Under-blanch-hours, which is usually two to three Changes in food
ing speeds up enzyme activity and is pounds of food per cubic foot of freezer worse than no blanching at all.

texture during
space. Overloading results in a long, freezing
slow freeze and a poor quality product.

Enzymes in fruits

Freezing involves the change of Place packages in contact with Enzymes in fruits can cause brown-water contained in the food from a liq-refrigerated surfaces in the coldest part ing and loss of vitamin C. People gener-uid to a solid (ice). When water freezes of the freezer. Leave a little space ally serve fruits raw, so instead of it expands, and the ice crystals formed between packages so that air can cir-blanching fruits to control enzyme activ-cause cell walls of food to rupture. As a culate freely. When the food is frozen, ity, they are treated with a chemical result, the texture of the product will be packages can be restacked close compound. The most common additive much softer when it thaws.

together.

is ascorbic acid (vitamin C). Ascorbic These textural changes are most To maintain top quality, store frozen acid may be used in its pure form or in noticeable in fruits and vegetables that foods at 0 degrees F or lower. This commercial mixtures of ascorbic acid have a high water content. For exam-temperature can be maintained in sep-and other ingredients such as sugar.

ple, when frozen lettuce thaws, it turns arate freezer units and in some combi-Some publications suggest using an limp and wilted. This is the reason veg-nation refrigerator-freezers. A freezer acid solution (citric acid or lemon juice) etables with a high water content, such thermometer can help determine the to control browning for a short time.

as celery and salad greens, are not actual temperature of your freezer.

These publications instruct you to place usually frozen (Table 1). It is also the Spoilage occurs more quickly and fruit in the acid solution while preparing reason why many frozen fruits are best shelf life is shorter when you store it for the freezer. Then place the fruit in served while they still contain a few ice frozen foods at a temperature higher freezer containers and either freeze it crystals. The effect of freezing on fruit than 0 degrees F. For example, the dry or cover the fruit with unsweetened tissue is less noticeable when fruit is same loss of quality in frozen beans fruit juice. Acid solutions work well as still partially frozen.

stored at 0 degrees F for one year will holding treatments for fruit but do not Textural changes due to freezing are occur in three months at 10 degrees F, prevent browning as effectively as not as apparent in products that are in three weeks at 20 degrees F and in treatment with ascorbic acid.

cooked before eating because cooking five days at 30 degrees F. Do not An alternative to holding fruit in an also softens cell walls. Textural attempt to save energy in your home acid solution is to prepare a syrup changes are also less noticeable in by raising the temperature of frozen (light, medium or heavy) that has high-starch vegetables, such as peas, food storage above 0 degrees F.

ascorbic acid added to it. After prepar-corn and lima beans.

Temperatures that fluctuate up and ing fruit for the freezer, it is then added down cause the ice in foods to thaw Rate of freezing
to the syrup and packaged for freezer slightly and then refreeze. Each time storage.

The amount of damage to cell walls this happens, smaller ice crystals 2

Human Environmental Sciences Extension Table 1. Foods that do not freeze well.

Foods

Usual use

Condition after thawing Cabbage1, celery, cress,

As raw salad
limp, water-logged, quickly cucumbers1, endive, lettuce, develop off-color, odor and parsley, radishes
flavor

Irish potatoes, baked or boiled In soups, salads, sauces or Soft, crumbly, water-logged, with butter
mealy

Cooked macaroni, spaghetti or As a side dish or in

When frozen alone for later use, rice
casseroles
mushy and has warmed-over flavor

Egg whites, cooked

In salads, creamed foods, Tough, rubbery, spongy
sandwiches, sauces, gravy or desserts

Meringue

In desserts

Toughens

Icings made from egg whites Cakes, cookies

Frothy, weepy

Cream or custard fillings Pies, baked goods

Separates, watery, lumpy

Milk sauces

For casseroles or gravies May curdle or separate

Sour cream

As topping, in salads

Separates, watery

Cheese or crumb toppings

On casseroles

Soggy

Mayonnaise or salad dressing On sandwiches (not in salads) Separates

Gelatin

In salads or desserts

Weeps

Fruit jelly

Sandwiches

May soak bread

Fried foods

All except French fried

Lose crispness, become soggy potatoes and onion rings

1Cucumbers and cabbage can be frozen as marinated products such as “freezer slaw” or “freezer pickles.” These do not have the same texture as regular slaw or pickles.

Moisture loss

Containers
become larger, further damaging cells (freezer burn)

for freezing
and creating a mushier product. Fre-quent changes in temperature also Moisture loss, or ice crystals evapo-Proper packaging material protects cause water to move out of the product rating from the surface area of a prod-the flavor, color, moisture content and resulting in a less juicy product that is uct, produces freezer burn. Freezer nutritive value of frozen foods from the generally lower in quality and nutritive burn appears as a fuzzy, grayish white dry climate of the freezer. Selection of value.

spot on the food surface. Freezer burn containers depends on the type of food For highest quality and nutritive is not harmful, but it causes off-flavors to be frozen, personal preference and value, use home frozen foods within the and dries out and toughens food. Pack-types that are readily available. Foods recommended storage times given in aging food in moisture/vapor-proof con-in larger containers freeze too slowly to Table 2. Food will still be safe to eat tainers or wrapping and storing food for result in a satisfactory product. For after the recommended time period is the recommended length of time will example, do not freeze fruits and veg-past if the freezer has been kept at 0
help prevent freezer burn. Covering fruit etables in containers larger than a half-degrees F or lower. However, the quali-with syrup and cooked meat with gravy gallon.

ty and nutritive value will be lower.

or sauce helps prevent freezer burn in In general, packaging materials for these products.

the freezer must have the following 3

Table 21. Storage times for home-frozen foods.

Food

Storage period at 0 degrees F

Butter

6 to 9 months

Margarine

12 months

Cheese
natural

6 to 8 weeks
processed

4 months

Cream (all kinds)

2 months
whipped

1 month

Eggs (whole, white, yolks) 9 to 12 months

Fish
fatty (perch, salmon, mackerel) 2 to 3 months
lean (cod, flounder, haddock, sole) 3 to 6 months

Fruit and fruit juice (except citrus) 8 to 12 months
citrus fruit and juice

4 to 6 months

Ice cream or sherbet

2 months

Meat
bacon

1 month
frankfurters and luncheon meat not recommended
ham

1 month
ground beef, lamb, veal

2 to 3 months
ground pork

1 to 2 months

Meat, roasts
beef

6 to 12 months
lamb, veal

6 to 9 months
pork

3 to 6 months

Meat, steaks, chops
beef

6 to 12 months
lamb, veal

1 to 2 months
pork

3 to 6 months

Milk, fresh fluid

1 month

Poultry (chicken, turkey, duck) Whole — chicken or turkey 12 months

— duck or goose

6 months

Cut up — chicken

9 months

— turkey

6 months

Giblets

3 months

Home prepared foods
bread

3 months
cake

3 months
casseroles (meat, fish, poultry) 3 months
cookies (baked and unbaked) 3 months
pies (unbaked fruit)

8 months

Vegetables
home frozen

10 months
purchased

8 months

Yogurt
plain

1 month
flavored

5 months

1For more extensive information on the recommended storage time for freezer foods, see MU publication GH 1505, Freezing Home Prepared Foods.

University of Missouri-Columbia 4
characteristics:

■ When food is packed in bags, press

Tip

■ Moisture- and vapor-proof; air from the bag. Press firmly, begin

■ Odorless, tasteless and grease-It is no bargain to recycle plas-at the bottom of the bag and move proof;
tic vegetable or bread bags and toward the unfilled top part of the

■ Foodgrade;
cottage cheese, ice cream or milk bag to prevent air from reentering.

■ Durable and leak-proof; Seal by twisting and folding back containers. They are not mois-

■ Not become brittle and crack at the top of the bag (gooseneck) and ture/vapor-proof and food frozen freezer temperatures;
securing with a string, good quality in them will lose moisture, flavor

■ Protect foods from absorption of rubber band or covered-wire twist and nutrients.

odors;
tie. Some bags are made specifical-

■ Easy to use, seal and label; ly for heat sealing. These should be

■ Designed for compact stacking and Flexible bags or wraps used only with a heating element economical use of freezer space; specifically made to seal storage

■ Reasonable cost.

Bags and sheets of moisture/vapor-containers. Never use an iron to There are two types of packaging proof materials (labeled freezer bags or heat seal these storage containers.

materials for use in home freezing: rigid freezer wrap) and heavy-duty aluminum

■ Seal rigid containers carefully. Use containers and flexible bags or wrap foil are suitable for dry-packed vegeta-a tight lid and keep the sealing made for freezer use. If labels of pack-bles and fruits, meats, fish or poultry.

edge free from moisture or food to aging material do not state that the Protective cardboard cartons may be ensure a good closure. Secure material is for freezer use, it probably used to protect bags and sheets loose-fitting covers with freezer isn3t.

against tearing and to make stacking tape.

Rigid containers
easier.

Meats may be packaged using Packaging and labeling foods either the drugstore wrap or the Rigid containers made of plastic or

■ Cool all foods and syrup before butcher wrap. Directions are given glass are suitable for all packs and are packing. This speeds up freezing in MU publication GH 1504, Freez-especially good for liquid packs as well and helps retain the natural color, ing Meat, Poultry, Fish, Eggs and as fragile or easily broken food. The flavor and texture of food.

Dairy Products.

straight sides on rigid containers make

■ Pack foods in quantities that will be

■ Label each package with the name the frozen food much easier to get out used for a single meal.

of the product, any added ingredi-and make it easier to stack foods in the

■ Follow directions for each individual ents, packaging date, number of freezer. Most rigid containers can be food to determine which can be servings or amount and the form of reused.

packed dry and which need added the food, such as whole, sliced, etc.

Regular glass jars, including jars liquid. Some loose foods such as Use freezer tape or self-adhesive made specifically for canning, break blueberries may be tray-packed labels and marking pens or crayons easily at freezer temperatures. If using (quick-frozen first on a tray before to label packages. Also label com-glass jars, choose wide mouth, dual packaging).

mercially frozen foods with the stor-purpose jars made for freezing and

■ Pack foods tightly leaving as little age date.

canning. These jars have been made to air as possible in the package.

Effect of freezing
withstand extremes in temperatures.

■ Most foods require headspace The wide mouth and straight sides between the packed food and clo-on spices and
allow easy removal of partially thawed sure to allow for expansion of the seasonings
foods. Covers for rigid containers food as it freezes. (See directions When preparing food for freezing, should fit tightly. If they do not, reinforce for individual foods included in other especially dishes that contain several the seal with freezer tape. Freezer tape home economics guides in the ingredients, it is more convenient to is especially designed to stick at freez-freezer series.) Foods that do not add all ingredients before placing the ing temperatures. Do not use masking need headspace include loose-pack food in the freezer. However, some tape because it will not stick at low vegetables such as asparagus and spices and seasonings change during temperatures.

broccoli, bony pieces of meat, tray-freezer storage. To avoid undesirable packed foods and baked products.

changes in the food product during Human Environmental Sciences Extension 5

Table 3. Sample freezer inventory.

Number of

Number of

Food
packages

Date frozen
packages removed

Green beans

Pints: 10

8/85

IIIII

Carrots

Quarts: 5

7/85

III

Corn

Pints: 20

7/85

IIIII I
freezer storage, note the following: amounts you will use within the recom-ommended storage times.

■ Pepper, cloves, garlic and synthetic mended storage period.

Keep the inventory in a handy place vanilla tend to become strong and Budget freezer space first for basic so food can be added and subtracted bitter;
foods such as meats, vegetables and without much trouble. Remember, the

■ Onions change flavor during freez-fruits. Then, if there is room, plan to simpler it is to use, the more you will ing;
freeze baked goods, main dishes, use it. You might want to use an index

■ Celery seasoning becomes strong; snacks or desserts.

card system with a separate card for

■ Curry may develop a musty off-fla-Keep contents organized. An orderly each food item. This makes it easy to vor;
freezer holds many more packages add items to the inventory and to deter-

■ Salt loses flavor and has a tenden-than a disorderly one. Stack similar mine the total amount of a specific food cy to increase rancidity of any item foods together. Packages you will use on hand. A sample freezer inventory is containing fat.

first should be the easiest to get to. Use shown in Table 3.

baskets, shelves, or dividers that are A freezer plan
furnished with the freezer to help orga-You get maximum convenience and nize the contents.

Tip
economy through carefully planning the Keep an inventory. You will always use of your freezer. The secret lies in know what is on hand if you keep an Season foods lightly before an easy management plan.

inventory of the foods that are in the freezing, and add additional sea-Plan the freezer contents. Freeze freezer. A current inventory can help sonings when reheating or serv-foods you need and use often. Freeze you plan meals and remind you to use ing.

only the foods your family likes and in old packages of food within their rec-For more information on this subject and many others, visit the MU Extension Publications Web site at: http://muextension.missouri.edu/explore

■ Issued in furtherance of Cooperative Extension Work Acts of May 8 and June 30, 1914, in cooperation with the United States Department of Agriculture. Ronald J. Turner, Director, Cooperative Extension, University of Missouri and Lincoln University, Columbia, MO 65211.

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$.75

GH 1501

Reprinted 6/03/5M