May
2004 May
2004
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Focus On: Freezing Foods in the freezer — are they safe? Every year, thousands of callers to the USDA Meat and Poultry Hotline aren’t sure about the safety of items stored in their own home freezers. We get plenty of similar calls to our Extension offices as well. It seems few people understand how freezing protects food. Here is some information on how to freeze food safely and how long to keep it. What can you freeze? You can freeze almost any foods. Some exceptions are cans of foods or eggs in shells. However, once the food (such as a ham) is out of the can, you may freeze it. Being able to freeze food and being pleased with the quality after defrosting are two different things. Some foods simply don’t freeze well at all. Examples are mayonnaise, cream sauce and lettuce. Raw meat and poultry maintain their quality longer than their cooked counterparts because moisture is lost during cooking. Is frozen food safe? Food stored constantly at 0°F will always be safe. Only the quality suffers with lengthy freezer storage. Freezing keeps food safe by slowing the movement of molecules, causing microbes to enter a dormant stage. Freezing preserves food for extended periods because it prevents the growth of microorganisms that cause both food spoilage and foodborne illness. Does freezing destroy bacteria and parasites? Freezing to 0°F inactivates any microbes — bacteria, yeasts and molds — present in food. Once thawed, however, these microbes can again become active, multiplying under the right conditions to levels that can lead to foodborne illness. Since they will then grow at about the same rate as microorganisms on fresh food, you must handle thawed items as you would any perishable food. Thorough cooking will destroy bacteria. Wild game and raw seafood can harbor parasites which may infect people. Commercial sub-zero freezing temperatures can kill these parasites but home freezing is less reliable. Consider the risk when offered sushi or ceviche. Thorough cooking will destroy all parasites. Freshness and quality. Freshness and quality at the time of freezing affect the condition of frozen foods. If frozen at peak quality, foods emerge tasting better than foods frozen near the end of their useful life. So freeze extras sooner rather than later. Store all foods at 0° F or lower to retain vitamin content, color, flavor and texture. Nutrient retention. The freezing process itself does not destroy nutrients. In meat and poultry products, there is little change in nutrient value during freezer storage. Enzymes. Enzyme activity can lead to the deterioration of food quality. Enzymes present in animals, vegetables and fruit promote chemical reactions, such as ripening. Freezing only slows the enzyme activity that takes place in foods. It does not halt these reactions which continue after harvesting. Enzyme activity does not
harm frozen meats or fish and is neutralized by the
acids in frozen fruits. But most vegetables that freeze well are low acid
and require a brief, partial cooking to prevent deterioration. This is
called "blanching." For successful freezing, blanch or partially
cook vegetables in boiling water or in a microwave oven. Then rapidly
chill the vegetables prior to freezing and storage. Consult Extension
Guide GH 1503 Freezing Vegetables for specific instructions. It can
ordered for $1 from your local Extension office or found on-line at: Packaging. Proper packaging helps maintain quality and prevent "freezer burn." It is safe to freeze meat or poultry directly in its supermarket wrapping but this type of wrap is permeable to air. Unless you will be using the food in a month or two, overwrap these packages as you would any food for long-term storage using airtight heavy-duty foil, plastic wrap or freezer paper, or place the package inside a plastic bag. Use these materials or airtight freezer containers to repackage family packs into smaller amounts or freeze foods from opened packages. It is not necessary to rinse meat and poultry before freezing. Freeze unopened vacuum packages "as is". If you notice that a package has accidentally torn or has opened while in the freezer, it is still safe to use; merely overwrap or rewrap it. Freezer burn. Freezer burn does not make food unsafe, merely dry in spots. It appears as grayish-brown leathery spots and is caused by air reaching the surface of the food. Cut freezer-burned portions away either before or after cooking the food. Heavily freezer-burned foods may have to be discarded for quality reasons. Color changes. Color changes can occur in frozen foods. The bright red color of meat as purchased usually turns dark or pale brown depending on its variety. This may be due to lack of oxygen, freezer burn or abnormally long storage. Freezing doesn’t usually cause color changes in poultry. However, the bones and the meat near them can become dark. Bone darkening results when pigment seeps through the porous bones of young poultry into the surrounding tissues when the poultry meat is frozen and thawed. The dulling of color in frozen vegetables and cooked foods is usually the result of excessive drying due to improper packaging or over-lengthy storage. Freeze rapidly. Freeze food as fast as possible to maintain its quality. Rapid freezing prevents undesirable large ice crystals from forming throughout the product because the molecules don’t have time to take their positions in the characteristic six-sided snowflake. Slow freezing creates large, disruptive ice crystals. During thawing, they damage the cells and dissolve emulsions. This causes meat to "drip"—lose juiciness. Emulsions such as mayonnaise or cream will separate and appear curdled. Ideally, a food 2-inches thick should freeze completely in about 2 ours. If your home freezer has a "quick-freeze" shelf, use it. Never stack packages to be frozen. Instead, spread them out in one layer on various shelves, stacking them only after frozen solid. Refrigerator-freezers. If a refrigerator freezing compartment can’t maintain zero degrees or if the door is opened frequently, use it for short-term food storage. Eat those foods as soon as possible for best quality. Use a free-standing freezer set at 0° F or below for long-term storage of frozen foods. And keep a thermometer in your freezing compartment or freezer to check the temperature. Length of time. Because freezing keeps food safe almost indefinitely, recommended storage times are for quality only. Refer to the freezer storage chart at the end of this article or download the excellent storage chart from Kansas State University at http://www.oznet.ksu.edu/library/FNTR2/L805.PDF If a food is not listed on the chart, you may determine its quality after defrosting. First check the odor. Some foods will develop a rancid or off odor when frozen too long and should be discarded. Some may not look picture perfect or be of high enough quality to serve alone but may be edible; use them to make soups or stews. Cook raw food and if you like the taste and texture, use it. Safe defrosting. Never defrost foods in a garage, basement, car, dishwasher or plastic garbage bag; out on the kitchen counter, outdoors or on the porch. These methods can leave your foods unsafe to eat. There are three safe ways to defrost food: in the refrigerator, in cold water or in the microwave. It’s best to plan ahead for slow, safe thawing in the refrigerator. Small items may defrost overnight; most foods require a day or two. And large items like turkeys may take longer — one day for each 5 pounds of weight. For faster defrosting, place food in a leak proof plastic bag and immerse it in cold water. (If the bag leaks, bacteria from the air or surrounding environment could be introduced into the food. Tissues can also absorb water like a sponge, resulting in a watery product.) Check the water frequently to be sure it stays cold. Change the water every 30 minutes. After thawing, refrigerate the food until ready to use. When microwave-defrosting food, plan to cook it immediately after thawing because some areas of the food may become warm and begin to cook during microwaving. Holding partially cooked food is not recommended because any bacteria present wouldn’t have been destroyed. Refreezing. Once food is thawed in the refrigerator, it is safe to refreeze it without cooking, although there may be a loss of quality due to the moisture lost through defrosting. After cooking raw foods which were previously frozen, it is safe to freeze the cooked foods. And if previously cooked foods are thawed in the refrigerator, the unused portion may be refrozen. If you purchase previously frozen meat, poultry or fish at a retail store, you can refreeze if it has been handled properly. Cooking frozen foods. Raw or cooked meat, poultry or casseroles can be cooked or reheated from the frozen state. However, it will take approximately one and a half times as long as if it were thawed. Remember to discard any wrapping or absorbent paper from meat or poultry. When cooking whole poultry, remove the giblet pack from the cavity as soon as you can loosen it. Cook the giblets separately. Read the label on USDA-inspected frozen meat and poultry products. Some, such as pre-stuffed whole birds, MUST be cooked from the frozen state to ensure a safely cooked product. Power outage in freezer. If there is a power outage, the freezer fails or if the freezer door has been left ajar by mistake, the food may still be safe to use. As long as a freezer with its door ajar is continuing to cool, the foods should stay safe overnight. If a repairman is on the way or it appears the power will be on soon, just don’t open the freezer door. A freezer full of food will usually keep about 2 days if the door is kept shut; a half-full freezer will last about a day. The freezing compartment in a refrigerator may not keep foods frozen as long. If the freezer is not full, quickly group packages together so they will retain the cold more effectively. Separate meat and poultry items from other foods so if they begin to thaw, their juices won’t drip onto other foods. For short term power outages — less than 6 hours — leave the door closed until the power returns. If the power is off for more than 6 hours, you may want to put dry ice, block ice or bags of ice in the freezer, or transfer foods to a friend’s freezer until power is restored. Use an appliance thermometer to monitor the temperature. If it’s freezing outside or if there’s snow on the ground, that might seem like a good place to keep food frozen until the power comes on. However, foods stored in the great outdoors are exposed to the sun, environmental contamination, roaming animals and birds. So keep food indoors. To determine the safety of foods when the power goes on, check their condition and temperature. If food is partly frozen, still has ice crystals or is as cold as if it were in a refrigerator (40°F), it is safe to refreeze or use. It’s not necessary to cook raw foods before refreezing. Discard foods that have been warmer than 40°F for more than 2 hours. Discard any foods that have been contaminated by raw meat juices. Dispose of soft or melted ice cream for quality’s sake. Frozen Cans. Canned goods stored in an unheated area may accidentally freeze. A slight breakdown of texture may result, but generally a single freezing and thawing does not adversely affect them. Be sure to check cans and jars of food that have been frozen for any breaks in the seals by setting them on a paper lined tray to check for leaks. Discard any food in a bulging can or one that has a broken seal or leaks. Adapted from: USDA Food Safety and Inspection Service, Focus on Freezing, 1994 and GH 1501 Freezing Basics, University of Missouri. Other May 2004 Articles:
Cynthia
Fauser
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