IF HOME freezing of food is to give American families all they expect, there is need for better equipment and better directions for handling food. People want to know what to look for when they are deciding which type of freezer to buy. They want to know what are the most suitable kinds and varieties of foods to freeze; how to select, prepare, and freeze them; how long to store frozen foods; and how to thaw or cook them.

To get the facts needed, scientists in industry, colleges, and the Department have been making investigations on home freezing and preparing and serving frozen products. Methods of treating and packing foods before freezing are compared as to their effectiveness in conserving palatability and nutritive value throughout freezing and storage, and methods of thawing or cooking and serving frozen foods are similarly studied. Texture, flavor, and color are given chief attention as factors affecting palatability. Ascorbic acid (vitamin C) is used as the chief guide to changes in nutritive value because it is sensitive to heat and oxidation and is soluble in water. Success in retaining ascorbic acid is therefore a good sign that other nutrients are also saved. A beginning has been made in studying changes in another sensitive vitamin, thiamine, especially in foods low in ascorbic acid.

To stop the action of enzymes and thus slow down changes in the palatability and nutritive value of frozen foods during storage, vegetables or fruits are often scalded before freezing. Harmless chemicals are sometimes used instead of scalding, especially for fruits or vegetables usually eaten raw. It is possible to prevent some changes by cutting off contact with the air, for example, by adding sirup to fruit.

We learned in our tests that if raw peaches (September Elbertas) were covered with a sirup containing a fourth of a teaspoon of crystalline ascorbic acid to a cup, darkening was prevented without appreciably altering flavor and texture. The treatment also added considerable ascorbic acid to the fruit at an extra cost of slightly more than 1 cent a pint.

Unless peaches were completely covered by sirup to protect them from air, darkening occurred during frozen storage or after thawing. If dry sugar was used (1 cup of sugar to 4% to 6 cups of fruit), it had to be dissolved completely in the juice from the fruit and the resulting sugar-juice sirup had to cover the fruit completely. Peaches also can be sliced, mixed with sugar and lemon juice, made into pies, and frozen. After 4 months, we found good retention of fresh flavor and no darkening of the peaches. Nectarines (Sure Crop and Garden State varieties) can be frozen satisfactorily after dipping in citric acid, 1 teaspoon per gallon.

Freezing applesauce is a good way to save early apples or others not suitable for winter storage. Baked apples also were frozen successfully.

Frozen blueberries retained their natural flavor well if packed in sirup or dry sugar and were successfully used in a variety of recipes. Most of these tests were done with seedlings; a few with Scammell and Jersey varieties. Cranberries retained their color and flavor well whether packed with or without sugar or sirup. The skins were tough, however, whether the berries were frozen raw or as cooked sauce.

Further work on fruit is under way to improve our methods for retaining natural texture, flavor, and appearance, as well as nutritive value.

Fruit purees were used as a base for home-made Velva Fruit. The freezing of purees is especially useful where there is fully ripe fruit which might otherwise go to waste.

Studies with asparagus, snap beans, broccoli, cauliflower, and peas indicate that satisfactory palatability and nutritive value can be maintained during freezing and storage when the vegetables are pretreated and frozen by practical home procedures. There was some loss of ascorbic acid as a result of scalding and freezing. There was also some loss of quality as indicated by the flavor and texture scores. Despite such losses, broccoli remained a rich source of ascorbic acid after freezing. It lost about one-third more during 9 months’ storage. Cauliflower is also high in vitamin C and retained its value through several months of storage before dropping gradually to about one-half its freshly frozen value at the end of a year. Peas, snap beans, and asparagus are low in ascorbic acid. They suffered only small losses during scalding and freezing and retained their small supply well during frozen storage. Further research is under way to establish for these and other vegetables the treatments that will best save palatability and nutritive value.

We found that scalding with steam was better for broccoli, and water scalding for peas and cauliflower. With asparagus it did not make much difference whether steam or boiling water was used. According to preliminary work, the same was true for snap beans. Recent intensive studies on the Tendergreen variety indicate, however, that snap beans scalded in boiling water retain the appearance of fresh cooked beans, even after 12 months of frozen storage, and are less subject to development of off-flavor and toughness than are steam scalded beans.

The vitamin C values of frozen beans do not change greatly during frozen storage but in this respect, also, water scalding appears to give somewhat better results.

The scalding time that gives best results depends on enzyme activity of raw samples, scalding medium (steam or water), amount of food being scalded, size of pieces, altitude, and so on. Hence, in setting up directions for a homemaker to use, the research workers selected conditions that should insure a good product even though there is no chance in the kitchen to check enzyme activity or make other technical tests. Besides the scald best suited to conditions, factors that were found to help keep losses low were: Keeping the fresh vegetables cool; processing as soon after harvesting as possible; cutting and scalding only small amounts at a time; and keeping scalded, cooled vegetables in the refrigerator until they can be put in the home freezer or community locker.

Comparison of methods for cooling after scalding showed that cooling in iced water (60° F.) gave most satisfactory results from the standpoint of time, manipulation of equipment, and attention required. No difference in retention of ascorbic acid or palatability was found as a result of the different cooling methods tried.

Whole eggs or separated yolks require suitable mixing before freezing to prevent undesirable changes. Frozen eggs must not only taste good but must retain their cooking quality. For instance, they must coagulate smoothly in custard and scrambled egg and produce light and stable foams for sponge cake.

Most meat and poultry can be frozen raw without special pretreatment. The meat should be cut as desired for cooking later. Ground meat can be shaped into cakes of convenient size. The use of condiments, especially salt, may affect the length of time such meat can be stored. Boning saves freezer space on some cuts. Very bony pieces, like the backs and wings of chicken, can best be cooked and the pieces of meat removed from bones before freezing.

Frozen prepared foods relieve the homemaker who buys such products of much of the drudgery and time required for food preparation. For the woman who freezes her own food, the work of preparation is of course merely removed by days, weeks, or months from the time of serving. This has advantages. For instance, the farmer’s wife can prepare in a slack season food to be served at harvesttime when the whole family is needed outside the kitchen, or when her own efforts should be directed toward preserving perishable fruits, vegetables, or meats for later use.

More research on factors that affect the quality of frozen prepared foods is under way. Results of preliminary studies on frozen baked goods indicate that rolls, biscuits, and cakes can be frozen and held successfully at least for short periods. Indications are that satisfactory storage time for baked goods may be relatively short, compared with that for meats, fruits, and vegetables. The freezing of baked products seems practical, however, as an economy measure for small families, as a means of postponing staling, or as a way of distributing the labor of cooking that otherwise might have to be done on a crowded and busy day.

The keeping quality is, of course, influenced by initial quality, as well as by techniques of handling and conditions of storage.

Fruit pies made and frozen during the summer can be baked and served in winter or spring when the supply of fresh fruits is more limited. Food and freezer space can be saved by preparing and freezing creamed chicken, for example, made from the bony pieces of birds at culling time.

Of the packaging materials available for wartime research, several were used during the course of the experiments. Heat-sealing Cellophane, which resists the passage of moisture or air, was found to give good results when used either inside or outside a stiff package. Where the protection of a stiff package was not feasible, as for large irregular cuts of meat or for pies, a wrapping of Cellophane was protected with stockinette. Angular package shapes were found to be better than round ones because they saved space when packed side by side in the freezer. A wider variety and adaptability of packaging materials for use in home freezing can be expected in the future. Two devices that can be made at home were developed to help the homemaker in packaging her food. One is a simple funnel for filling cartons. The other is a stand for use in heat- sealing food packages.

Operating characteristics of seven makes of home freezers were studied. More work needs to be done to establish the relationship between the results of engineering tests and the performance-in-use values that indicate a satisfactory piece of equipment. On the basis of the work done to date, however, it appears that in available chest-type cabinets, under normal operating conditions, temperatures in the upper fifth or tenth of the compartments are higher than that recommended for satisfactory storage of frozen food. A separate freezing compartment is desirable to reduce temperature variation in the stored frozen food while a new load is being frozen. Freezing compartments, however, should not be as large as those in many available freezers.

To find out how well home freezers could maintain low temperatures in the frozen food when the cooling system is not working (as when a storm cuts off electric current), five representative freezers were studied. With the current off, the time it took packages to reach the melting point of ice (32° F.) varied with the freezer and with the amount and position of frozen food in the cabinet. In one freezer, with the storage compartment filled, it was 44 hours before the first package reached 32° F. In another, similarly packed, it took 80 hours. The freezer that took 44 hours to reach 32° F., when full, took 33 hours when only one-fourth full. There is need for better insulation at certain points in the freezers in order to slow down the passage of heat from outside into the food compartment.

It is better to use dry ice (solid carbon dioxide) when the freezer is not working than to depend on blankets or other outside insulation to keep down the temperature of the frozen food. Freezing rates have been recorded under varied conditions. In a freezing compartment with a fan, the average time required for food to reach 0° F. was found to be 7 to 8 hours for small loads (6 to 12 pounds of food) and 15 to 20 hours for large loads (30 to 40 pounds of food). With a load of about 20 pounds of snap beans in pint cartons in a freezer without a fan, 24 hours elapsed before all the food reached 0° F. Double that load (about 40 pounds), in a freezer with a fan, reached 0° F. in only 15 hours. Little difference was found in the time needed to reach 0° F. in foods packaged in different kinds of cartons. A comparison of food in cartons with food frozen on open trays showed that green snap beans and asparagus in closed, sealed cartons needed 7 hours to reach 0° F. whereas those frozen on open trays required only 1 hour.

These figures help to set up instructions for homemakers as to when food may be ready to move from the freezing to the storage compartment. They cannot be used to indicate whether the rate of freezing affects palatability and nutritive value in the final product. No clearly defined results on this aspect of freezing rates are available at present.

Investigations were also started to determine the temperature limits allowable for long-term and short-term frozen storage. If higher temperatures and wide temperature fluctuations could be used, the cost of manufacturing and operating home freezers would be less. In cooperative work with Cornell University, it was found that with temperatures fluctuating between 0° F. and 20° F. foods tend to dry out unless properly packaged. It was also found that more ascorbic acid is lost as the temperature is raised. Thiamine in pork is not significantly affected by the temperature conditions or period of storage in the freezer. Rancidity, however, was greatly hastened when the pork was exposed to temperature above 0° F. The palatability of all products except meat was lower at 10° F. storage or following 0° F. to 20° F. fluctuations than at 0° F. All palatibility factors for pork were affected by length of storage but some were not affected by temperature.

If the temperature usually prevailing in the freezing compartment of a home refrigerator proves to be low enough for brief storage, frozen foods can be brought from community lockers or purchased and kept on hand for a few weeks by people who do not own home freezers. Studies are under way in cooperation with Iowa State College which will help to answer the question of allowable temperatures for short-term frozen storage. Results now available indicate considerable differences in frozen foods with respect to changes in palatability and vitamin C value. The temperatures used were 0, 5, 10, and 20° F.; the storage times were 2, 4, 6, and 8 weeks.

The concentration of the vitamins, thiamine and niacin, did not change in any of the foods studied—peaches, rhubarb, pineapple, soybeans, corn, peas, and snap beans.

Studies have recently been completed on frozen peas. Although thawed in different ways, the ascorbic acid value before cooking varied very little, from 54.5 to 51.6 milligrams per 100 grams. Frozen peas cooked in a small amount of water without previous thawing retained 85 percent of their uncooked value. A downward trend from this value was apparent for peas cooked as above but thawed 3 hours at room temperature, 9 hours in the refrigerator, or 33 hours in the refrigerator. The retentions were 81 percent, 76 percent, and 72 percent respectively. No differences in palatability were observed. From results on this one vegetable, it appears that, when possible, frozen vegetables should be cooked without preliminary thawing. On the other hand, if some unexpected event forces the holding of a thawed vegetable for an extra 24 hours in the refrigerator this will probably not affect palatability. It will result in some loss of vitamin C.

THE AUTHOR
Esther L. Batchelder is head of the Food and Nutrition Division of the Bureau of Human Nutrition and Home Economics. Besides general responsibility for the work of her Division, she has taken an active part in home dehydration and freezing research. Before joining the Bureau in 1942, Dr. Batchelder was director of Home Economics at Rhode Island State College. She has taught and done research in nutrition at the University of Arizona, the State College of Washington, and Columbia University.

ACKNOWLEDGMENTS
Many people have contributed to the results reported here. It is possible to mention by name only the project leaders, Lenore Sater and Enid Sater, Earl C. McCracken, Mary E. Kirkpatrick, and Sophie Marcuse, who, with the writer, have worked on various phases of the research at Beltsville. Acknowledgment is also due our cooperators, Louise Peet and Pearl Swanson of the Iowa State College and Experiment Station and Willis Gortner and Faith Fenton of Cornell University.

Before making recommendations to American homemakers, research workers test scores of processes and kinds of equipment. To study changes in freezing food at home, Equipment Specialist Dorothy Skinner (above) inserts a thermocouple into a carton of liquid. Below, Physicist Earl C. McCracken connects thermocouples to an automatic recorder of temperature changes and makes notes from it. In an article that begins on page 801 [the article on this page above -ASC], Esther L. Batchelder says: “People want to know what are the most suitable kinds and varieties of foods to freeze; how to select, prepare, and freeze them; how long to store frozen foods; and how to thaw or cook them.”