Frozen Food Safety & Quality
Freezing delays spoilage and keeps foods safe by preventing microorganisms from growing and by slowing down the enzyme activity that causes food
to spoil. As the water
in the food freezes into ice crystals, it becomes unavailable to those microorganisms that need it for growth. However, most microorganisms, (with the exception of parasites), remain alive when frozen so foods must be handled safely both before freezing and once defrosted.
Freezing has very little effect on the nutrient content of foods. Some fruits and vegetables are blanched (immersed in boiling water
for a short period) before freezing to inactivate enzymes and yeasts that would continue to cause food spoilage, even in the freezer
. This process can cause some of the vitamin C (15 to 20%) to be lost
. In spite of these losses, vegetables and fruits are frozen in peak condition soon after harvesting and are often higher in nutrients than their "fresh" counterparts. Harvested produce can sometimes take many days to be sorted, transported and distributed to stores. During this time, vitamins and minerals can be slowly lost
from the food. Fresh soft fruits and green vegetables can lose as much as 15% of their vitamin C content daily when kept at room temperature.
There are almost no vitamin and mineral loses from frozen meats, fish
and poultry because protein, vitamins A and D and minerals are not affected by freezing. During the defrosting process, there is a loss of liquid containing water-soluble vitamins and mineral salts, which will be lost in the cooking
process if this liquid is not recovered.
Freezing can damage some foods because the formation of ice crystals causes breakage of the cell membranes. This has no adverse effects in terms of safety
, (indeed some bacterial cells would also be killed), however the food loses its crispness or firmness. Examples of foods that do not tolerate freezing well include salad vegetables, mushrooms and soft fruits.
Foods with higher fat contents, such as cream and some sauces, tend to separate when frozen.
freezing rapidly freezes foods so that smaller ice crystals are formed. This cause less damage to cell membranes so that quality is even less affected.
What Can You Freeze?
You can freeze almost any food. Some exceptions are canned food 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. 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?
Previously uncontaminated 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 & 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.
Trichina and other parasites can be destroyed by sub-zero freezing temperatures. However, very strict government-supervised conditions must be met. It is not recommended to rely on home freezing to destroy trichina. Thorough cooking will destroy all parasites.
Freshness & 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 items you won't use quickly sooner rather than later. Store all foods at 0̊ F or lower to retain vitamin content, color, flavor and texture.
The freezing process itself does not destroy nutrients. In meat and poultry products, there is little change in nutrient value during freezer storage
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 a cookbook
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, (freezer) plastic wrap or freezer paper, or place the package inside a (freezer) plastic bag. Use these materials or airtight freezer containers to repackage family
packs into smaller amounts. 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 been torn or has opened while food is in the freezer, the food is still safe to use; merely overwrap or rewrap it.
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 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 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 hours. 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/lid is opened frequently, use it only for short-term food storage. Eat those foods as soon as possible for best quality. Use a freezer set at 0̊ F or below for long-term storage of frozen foods. Keep a thermometer in your freezing compartment or freezer to check the temperature. This is important if you experience power-out or mechanical problems.
Length of Time
Because freezing keeps food safe almost indefinitely, recommended storage times are for quality only.
To determine food 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.
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, approximately 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, cook immediately.
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.
Once food is thawed in the refrigerator, it is safe to immediately 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 immediately freeze the cooked foods. If previously cooked foods are thawed in the refrigerator, you may immediately refreeze the unused portion.
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 the usual cooking time for food which has been 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.
Freezer Storage Chart (0 ̊F)
Note: Freezer storage is for quality only. Frozen foods remain safe indefinitely.
~ Months Frozen Storage
Bacon and Sausage 1 to 2 Months
Casseroles 2 to 3
Egg whites or egg substitutes 12
Frozen Dinners and Entrees 3 to 4
Gravy, meat or poultry 2 to 3
Ham, Hotdogs and Lunchmeats 1 to 2
Meat, uncooked roasts 4 to 12
Meat, uncooked steaks or chops 4 to 12
Meat, uncooked ground 3 to 4
Meat, cooked 2 to 3
Poultry, uncooked whole 12
Poultry, uncooked parts
Poultry, uncooked giblets 3 to 4
Poultry, cooked 4
Soups and Stews 2 to 3
, uncooked 8 to 12
Safe Cooking Temperatures
Use a thermometer to test for cooked food 'doneness':
Ground Beef/Pork @ 160 Deg. F (71C)
Ground Chicken/Turkey @ 175F (80C)
Roast/Steaks RARE @ 140F (60C)
Roasts/Steaks MEDIUM @ 160F (71C)
Chops MEDIUM @ 160F (71C)
Whole Turkey/Chicken @ 180F (82C)
Chicken/Turkey Peices @ 170F (77C)
Egg Dishes/Casseroles @ 160F (71C)
Reheated Leftovers @ 165F (74C)