Published on March 6, 2008
Freezing Fruits and Vegetables at Home: Freezing Fruits and Vegetables at Home Cooperative Extension Service The University of Georgia College of Family and Consumer Sciences Advantages of Freezing: Advantages of Freezing Many foods can be frozen. Good natural color, flavor and nutritive value can be retained. Texture usually better than for other methods of food preservation. But this is personal preference. Foods can be frozen in less time than they can be dried or canned. Advantages of Freezing: Advantages of Freezing Simple procedures. Adds convenience to food preparation. Proportions can be adapted to needs unlike other methods. Kitchen remains somewhat cool and comfortable. Disadvantages ofFreezing Foods: Disadvantages of Freezing Foods Texture of some foods is undesirable because of changes due to the freezing process. Initial investment and cost of maintaining a freezer is high. Storage space is limited by how much the freezer will hold. How Freezing Affects Food: How Freezing Affects Food Enzymes in Vegetables and Fruits To prevent color and flavor changes, as well as loss of some nutrients, enzymes should be controlled. Are slowed down but not destroyed during freezing. (Enzymes are small proteins in foods that start or help with reactions, such as those that cause browning, off-flavors, mushiness, etc.) How Freezing Affects Food: How Freezing Affects Food Enzymes in Vegetables Are destroyed by heat, called blanching, before packaging and freezing. Enzymes in Fruits Usually controlled by ascorbic acid (also called vitamin C) or some other additives. Fruits are usually not blanched, but can be. People like them raw and uncooked. How Freezing Affects Food: How Freezing Affects Food Rancidity Another natural change that causes off-flavors, particularly in fatty foods. Not a common problem in fruits & veggies. Will continue to happen at freezer temperatures, but slower than at warmer temps. Best control is to keep as much air out of the package as possible. How Freezing Affects Food: How Freezing Affects Food Textural Changes The water in food freezes and expands. Ice crystals cause the cell walls of fruits and vegetables to rupture, making them softer when thawed. Some vegetables with very high water content do not freeze well: celery, lettuce, some tomatoes. How Freezing Affects Food: How Freezing Affects Food Rate of Freezing is Very Important Freeze Foods Quickly! Best Advice for Freezing: Best Advice for Freezing Freeze foods quickly. Set freezer temperature at -10o F at least 24 hours ahead of freezing large quantities of fresh food. Spread packages out around the freezer, until frozen, then stack. Hold at 0oF for best quality. Best Advice for Freezing: Best Advice for Freezing What happens when the freezer is above 0oF ? Best Advice for Freezing: Best Advice for Freezing What happens when the freezer is above 0oF ? Shelf life (storage time) for best quality is shorter. Vegetable Storage: Vegetable Storage Temperature 0o F. 5o F. 10o F. 15o F. 20o F. 25o F. 30o F. For same final quality: Length of Storage 1 year 6 months 3 months 6 weeks 3 weeks 10 days 5 days How Freezing Affects Food: How Freezing Affects Food Fluctuating Freezer Temperatures Ice in food thaws a little and then re-freezes. Ice crystals get bigger each time. Mushiness because large ice crystal growth damages cells more and more. Moisture pulled from product. Other quality losses speeded up due to higher temperatures. Moisture Loss Freezer burn – tough and dry, but safe. Freezer Selection: Freezer Selection Consider Size Shape Efficiency Defrosting features Available floor area Amount of freezer space needed Freezer Selection: Freezer Selection What size? General Rule - Allow 6 cubic feet of freezer space per person in family. (3 cubic feet per person may be adequate if other methods of food preservation are used). Standard Freezer Capacity: 35 pounds of frozen food per cubic foot of usable space. Types of Freezers: Types of Freezers Upright 6 to 22 cubic feet Convenient Uses small floor space Easy to load and unload Types of Freezers: Types of Freezers Chest 6 to 32 cubic feet Takes more floor space More economical to buy and to operate than upright Loses less cold air when opened Types of Freezers: Types of Freezers Refrigerator - Freezer Combination 2 to 6 cubic feet of freezer space. Freezer may be above, below or beside refrigerated area. Be sure temperature in freezer can be maintained at 0 degrees F. or less. Types of Freezers: Types of Freezers Other features to consider Self defrosting or manual defrost. Receptacle clips – prevent accidental disconnecting. Door locks. Drains for defrosting. Location and Placementof Freezer: Location and Placement of Freezer Place in convenient, cool, dry, well-ventilated area. Do not place by stove, range, water heater or in the sun. Do not push flush against wall. Leave space for air circulation and cleaning. Be sure freezer is level. General Freezing Instructions: General Freezing Instructions Selection of Food Freezing does not improve quality. Choose highest quality available. Freeze promptly. Remember some foods don’t freeze well. Preparation Work under sanitary conditions. Follow recommended procedures. Packaging MaterialsGood Qualities: Packaging Materials Good Qualities Moisture-vapor resistant. Prevents transfer of moisture and air in and out of the package. Durable and leak-proof. Does not become brittle and crack at low temperatures. Resistant to oil, grease or water. Protects foods from absorption of “off” flavors or odors. Easy to seal and label. Types of Packaging Materials: Types of Packaging Materials Rigid Containers Plastic freezer containers. Wide-mouth canning/freezing jars. Good for liquids or soft, juicy, or liquid-packed foods. May be reusable. Hold their shape and can be stored upright. Types of Packaging Materials: Types of Packaging Materials Non-Rigid Containers Bags Wrappings – plastic (such as polyethylene), heavy-duty aluminum foil, laminated paper Good for firm, non-juicy foods. Packing Foods to be Frozen: Packing Foods to be Frozen Food must be cool before freezing. Ice water bath after blanching. Pack in serving size quantities. Usually up to 1 quart. Especially when whole package must be thawed to get out what is needed. Packing Foods to be Frozen: Packing Foods to be Frozen Pack foods tightly – Avoid trapped air (oxygen). Not to waste space. However, most foods need headspace or room for some expansion at the top, except uneven vegetables like broccoli and asparagus, bony pieces of meat, tray-packed foods, and breads. Packing Foods to be Frozen: Packing Foods to be Frozen Use tight lid on rigid containers. Keep sealing edges clean and dry. Use freezer tape over seams of looser-fitting covers. Trapped food or liquids in sealing area will freeze, expand, and loosen seal. Press all air from bagged foods. Except for headspace. Seal non-zippered bags by twisting the loose top, and then folding the top of it down over itself (gooseneck). Secure with twist-tie, rubber band or string. Labels: Labels Name of product Added ingredients Form of food - halves, whole, ground, etc. Packaging date Number of servings or amount 9/15/02 Ground Beef 1 pound Freezing Guidelines: Freezing Guidelines 1. Freeze foods at 0oF or lower. 24 hours in advance of freezing large quantities of food, set freezer at -10oF or lower. 2. Freeze foods immediately after prep. Do not overload freezer with unfrozen food. Freeze amount that will freeze in 24 hours (2 to 3 pounds of food per cubic foot). 4. Pack already frozen foods together so they do not thaw. Freezing Guidelines, cont.: 5. Place unfrozen foods in contact with surfaces and in coldest parts of freezer. 6. Leave space around packages so cold air can circulate. 7. When packages are frozen, organize freezer into types of food. 8. Arrange frozen foods so that the foods frozen longer can be used first. 9. Keep a frozen foods inventory up to date. 10. Check thermometer periodically. Freezing Guidelines, cont. Freezing Fruits: Freezing Fruits Frozen in many forms – Whole, sliced, crushed, juiced. Best quality – Optimum maturity and freshness. Immature or overripe both produce lower quality when frozen. Wash and work with small amounts at a time to preserve best quality. Preventing Fruit DarkeningDuring Preparation(Peeling, slicing, etc.): Preventing Fruit Darkening During Preparation (Peeling, slicing, etc.) 1 tsp (3000 mg) ascorbic acid to one gallon of cool water Commercial ascorbic acid mixture Heating the fruit The following do not work as well: Citric acid solution Lemon juice Sugar syrup Salt/vinegar solution Preventing Discoloration During Freezing: Preventing Discoloration During Freezing Ascorbic Acid Most economical Powdered or tablet form 1/2 t. powdered ascorbic acid = 1500 mg For tablets, use number needed for desired milligrams (for example, 3 x 500 mg tablets = 1500 mg) Tablets must be crushed well Preventing Discoloration During Freezing: Preventing Discoloration During Freezing Ascorbic Acid Use amount specified for each fruit. In syrup or liquid packs - add powdered ascorbic acid to the covering liquid. Usually ½ tsp (1500 mg) per quart of syrup. Preventing Discoloration During Freezing: Preventing Discoloration During Freezing Ascorbic Acid (con’t) In sugar or dry packs, dissolve the powdered ascorbic acid in 3 T. in cold water and sprinkle over fruit. In sugar packs, before adding sugar. Usually ¼ to ½ tsp (750 to1500 mg) per 3 T. water for each quart of fruit. For crushed fruit, purees or juices, mix the powdered ascorbic acid with the prepared fruit. Usually about ¼ tsp (750 mg) or less per qt. of fruit. Preventing Discoloration During Freezing: Preventing Discoloration During Freezing Ascorbic Acid Mixtures “Fruit Fresh” and others. These have some other added ingredients. Follow package directions to obtain correct strength of ascorbic acid. Preventing Discoloration During Freezing: Preventing Discoloration During Freezing Citric Acid or Lemon Juice Not as effective as ascorbic acid. May mask flavors of fruits. Steaming Best for fruits that will be cooked before use. Follow directions in freezing publications for times. Sweetened Packs for Fruit: Sweetened Packs for Fruit Syrup Pack Better texture. Not needed for safety. Fruits should be covered with syrup. Place crumpled water-resistant paper in top of container. Preparing Peaches in Syrup: Preparing Peaches in Syrup Sweetened Packs for Fruit: Sweetened Packs for Fruit Sugar Pack Sliced soft fruits (strawberries, peaches, etc.) make their own syrup when mixed with the right proportion of sugar. Layer fruit and sugar in bowl or pan. Allow mixture to stand 15 minutes to make juice or “syrup” before packaging. Unsweetened Packs for Fruit: Unsweetened Packs for Fruit Dry Pack Good for small whole fruits such as berries that don’t need sugar. Simply pack into containers and freeze. Or may be frozen individually, in single layer, on a tray first. “Tray pack” – next slide Dry Tray Pack for Fruit: Dry Tray Pack for Fruit Fruit pieces may be frozen individually, in single layer, on a tray first. Freeze until firm then package in rigid container or bag. Will pour out of container easily when frozen. Dry “Tray” Pack for Fruit: Dry “Tray” Pack for Fruit Can remove only the amount needed at one time. Fruit pieces retain shapes. Fruit pieces do not “clump” as when packed directly into containers or with sugar syrup. Unsweetened Packs for Fruit: Unsweetened Packs for Fruit Pectin Syrup Good for strawberries and peaches. Mix 1 package powdered pectin and 1 cup water. Bring to boil, boil 1 minute. Remove from heat, cool and add 1-3/4 cups more water. Water or Unsweetened Juice Packs Texture will be mushier. Color poorer. Freezes harder, takes longer to thaw. Packs for Purees or Juices: Packs for Purees or Juices Pack as is, with or without sugar. Add ascorbic acid if light-colored. Sugar Substitutes: Sugar Substitutes May be used in the pectin syrup, juice or water packs. Or could be added just before serving. These do not help with color retention or texture, like sugar does. Use amounts on product labels or to taste. Freezing Vegetables: Freezing Vegetables Select young, tender, high-quality vegetables. Sort for size and ripeness. Wash and drain before removing skins or shells. Wash small lots at a time, lifting out of water. DO NOT SOAK. Work in small quantities, preparing as directed. Preventing Flavor and Color Changes in Vegetables: Preventing Flavor and Color Changes in Vegetables Blanching Primary method to destroy enzymes for vegetables. Will also soften hard veggies to make packaging easier. Will also remove some microorganisms. Under-blanching can be harmful; it will stimulate enzymes and not destroy them. Check required blanching times for each food. How to Blanch Vegetables: How to Blanch Vegetables Use specific directions. Work in small quantities. How to Blanch Vegetables: How to Blanch Vegetables In Boiling Water Use blancher with lid or a kettle with basket and lid. Have 1 gallon water per 1 lb. of vegetables. Place vegetables in blanching basket. Lower vegetable into vigorously boiling water. Put lid on. Water should hardly stop boiling or return to a boil within a minute. If water keeps boiling, begin timing immediately. Otherwise, wait for water to come back to a boil. How to Blanch Vegetables: How to Blanch Vegetables Steam Blanching Use kettle with tight lid and basket. 1” to 2” of boiling water in bottom of pan. Vegetable should be in a single layer in basket. Start timing when covered. Takes 1-1/2 times longer than water blanching. Check times, however, for each food. How to Blanch Vegetables: How to Blanch Vegetables Microwave Blanching Not widely recommended at this time. May not be effective – enzymes not inactivated completely by uneven heating. Usually does not save time. Have to do very small quantities. If you have directions from a source you trust, try small quantities at first and see if you like the quality after a period of frozen storage. This is not a safety issue, as long as frozen food is always stored frozen, but improper blanching will affect quality. How to Blanch Vegetables: How to Blanch Vegetables After blanching in water or steam, cool immediately in cold water. Change water frequently or use running water or iced water (1 lb. ice per 1 lb. vegetable). Cooling time should be the same as the blanching time. Drain thoroughly. Types of Pack for Vegetables: Types of Pack for Vegetables Dry Pack Pack after the vegetables are blanched, cooled, and drained. Pack quickly, pushing air out of package as you work towards top. Types of Pack for Vegetables: Types of Pack for Vegetables Tray Pack After draining, spread pieces in a single layer on a shallow pan. Freeze firm. After first hour, check often. Package quickly, pushing air out as you work. Thawing Foods for Serving: Thawing Foods for Serving Fruits Best if served with ice crystals. Thaw: In refrigerator - 6 to 8 hours per pound of fruit in syrup. At room temperature - 1 to 2 hours per pound. At room temperature in cool water - ½ to 1 hour per pound. In microwave oven - follow manufacturer’s instructions. Thawing Foods for Serving: Thawing Foods for Serving Dry sugar packs thaw faster than syrup packs. Unsweetened packs thaw the slowest. When used in recipes, allow for added sugar and more juice. Thawing Foods for Serving: Thawing Foods for Serving Vegetables Cook without thawing. Corn-on-the-cob should be partially thawed so cob will be hot. Leafy greens cook more evenly if partially thawed. Oh No!: Oh No! You’ve done all this work … and the freezer stops running! Freezer Emergencies: Freezer Emergencies If know power will be off, set freezer controls on -10oF to -20oF immediately. Do NOT open the door. Foods stay frozen longer if freezer is full, well-insulated and in cool area. Full freezer - keeps 2 to 4 days. Half-full freezer - 24 hours. Freezer Emergencies: Freezer Emergencies If power interruption will be longer than 1 to 2 days: Use dry ice: 50 lbs. - keeps full 20 cubic foot freezer below freezing for 3 to 4 days. 50 lbs. - keeps half-full freezer for 2 to 3 days. Freezer Emergencies: Freezer Emergencies Place dry ice on boards or heavy cardboard on top of food. Do not touch dry ice to skin. Do not open freezer. Room should be ventilated. Refreezing Thawed Foods: Refreezing Thawed Foods Texture will not be as good. General Rule: Refreeze if freezer temperature is still 40oF or below OR if ice crystals are still present in the food. Disclaimer and Credits: Disclaimer and Credits Disclaimer: Trade and brand names are used only for information. The Cooperative Extension Service, University of Georgia College of Agricultural & Environmental Sciences and College of Family & Consumer Sciences, and the U.S. Department of Agriculture do not guarantee nor warrant published standards on any product mentioned; neither does the use of a trade or brand name imply approval of any product to the exclusion of others which may also be suitable. Document Use: Permission is granted to reproduce these materials in whole or in part for educational purposes only (not for profit beyond the cost of reproduction) provided the author and the University of Georgia receive acknowledgment and this notice is included: Reprinted (or Adapted) with permission of the University of Georgia. Andress, E.L. 2003. Freezing fruits and vegetables at home (slides). Athens, GA: The University of Georgia, Cooperative Extension Service. This material is based upon work supported by the Cooperative State Research, Education, and Extension Service, U.S. Department of Agriculture, under Agreement No. 00-51110-9762.