Bulletin No. 42 May 1943 FREEZING FRUITS AND VEGETABLES
Freezing Fruits and Vegetables w. E. PYKE and A. M. BINKLEy 1 Fruits for Freezing The fruits most commonly frozen and stored in frozen-food lockers are strawberries, raspberries, sour cherries, peaches, and apricots. Apples, grapes, plums, and gooseberries are not often frozen, although they yield a satisfactory product when properly handled. Varieties for Freezing In general the fruit varieties adapted and recommended for growing in a particular locality in Colorado will be satisfactory for freezing. Table 2' lists the more satisfactory varieties for freezing preservation. Quality-Maturity-Selection of Fruit The more perishable fruits should be harvested when the quality and flavor are highest and then should be packed and frozen the same day they are harvested. It is important to pick fruit at the proper stage of maturity. Tree- or plant-ripened fruit has better flavor and quality if handled quickly and frozen promptly. Do not pack fruit that has been damaged by insects, diseases, bruises, internal breakdown, or that is overripe or immature. More care is necessary in selecting fruit for freezing than for canning if the correct flavor is to be preserved in the frozen product. Vegetables for Freezing The vegetable crops most commonly preserved by freezing are: Peas, lima beans, sweetcorn, spinach, broccoli, snap beans, and asparagus. Other crops that can be frozen successfully are: Carrots, beets, turnips, squash, and greens such as beet tops and Swiss chard. However, these items are not so commonly found in frozen-food lockers. Lettuce, celery, tomatoes, cantaloups, honeydew melons, and cabbage are not usually preserved by freezing. Selection and Handling of Vegetables for Freezing Some varieties are better than others "Then frozen, but the variety must be adapted to local growing conditions as far as yield and quality are 'concerned. The mere selection of a variety 1 PYke, professor of food research: Binkley. horticulturist. Colorado Agr icultural Exper-Im e n t Statio n.
4 COLORADO STATE COLLEGE Ext. Bul. D-42 will not insure a satisfactory frozen product. Oftentimes a wellselected variety suitable for freezing may result in a low-quality product because it has been poorly processed, not picked at the right stage of maturity, or not handled or prepared properly for freezing. Varieties which are of high quality for table use generally are also desirable for freezing. Early smooth-seeded types of garden peas, such as Alaska, are not recommended for quick freezing. The hybrid sweetcorns have been found to be generally more satisfactory for freezing than standard open-pollinated varieties. This is because the yield, uniformity of maturity, and quality of hybrid varieties are often better. Satisfactory Freezing Varieties The varieties listed in table 3 are found to be generally satisfactory for freezing. The best quality, flavor, and condition will be preserved in the more perishable vegetables if they are packed and frozen the same day they are harvested. Harvest at Proper Stage of Maturity Harvesting at the proper stage of maturity is important for sweetcorn, pod peas, lima beans, snap beans, and asparagus. The quality and flavor of these vegetables are rapidly reduced by high temperatures (75 0 F. or above) after harvesting. Successful Freezing of Fruits and Vegetables Prompt Handling and Cleanliness of Paramount Importance Vegetables and perishable fruits should be thoroughly cleansed and handled promptly. In the high-altitude regions of the Rocky Mountain West there is no reason for using wilted produce of poor quality. Ice and cold water are abundant and can be used to advantage to keep food materials fresh. Produce deteriorates rapidly after harvesting unless it is kept cold and moist. Early-morning harvesting is always advantageous. The enzymes which serve to carryon many of the life processes of the plant cells are largely responsible for deterioration changes. Since this deterioration or food breakdown continues even at low temperatures, it is necessary to blanch all vegetables (except perhaps rhubarb) and fruits not immersed in sirups or otherwise preserved. The heat treatment of blanching inactivates the enzymes. Preparation and Blanching Procedures Procedures for the preliminary preparation and blanching of fruits and vegetables for freezing are, outlined in tables 4 and
May 1943 FREEZING FRUITS AND VEGETABLES 5 5. Blanching times given are those that have been found suitable in our experiments for the higher altitudes of this region (5,000 to 10,000 feet). Steam-blanching is generally superior to dipscalding in boiling water. Steam-blanching may be carried out above actively boiling water in a lid-covered container. Steam must be produced abundantly. A home-made wire basket of hardware cloth (wire mesh) may be used to hold the food material during blanching. Effective and rapid heat penetration is desired, so overloading should be avoided. For dip-scalding the same containers may be used, but a larger quantity of actively boiling water is necessary. The food materials should be cooled quickly after blanching, either by spreading thinly in an air blast (fan) or plunging quickly into cold water and then draining. TABLE I.-Quantities needed for preparation of sugar sirups Percentage of Sugar in Sirup 30 40 50 60 and brine. Sugar 1 cup 1 cup 1 cup 1* cups Water 2~4 cups 2 cups % cup 1 cup Sirups should be prepared and then cooled before they are used for freezing. Substitute Sugar-Saving Sirups Sugar Sugar substitute 'Vater Approximate sweetening power (percentage of sugar sirup) Beet sugar 8\veetose corn sirup Beet sugar Sweetened corn sirup" 1 cup ~8 cup Ill, cups 1 cup 11,';1 cups 1 ~>~ cups 40 percent 50 percent 2-Percent Brine (approximate) Salt contain Dissolve 5 level tablespoons of salt per gallon of water. ing no added, free-pouring ingredients should be used. S weetened corn sirup is prepared by dissolving- ~2 oz. of saccharine :soluble in %. cup of hot wat e r and stirring the solution into a IO-pound pail of co r n sirup.