Chapter 21

How Freezing, Canning, Drying, and Zapping Protect Your Food

IN THIS CHAPTER

Freezing food safely

Creating canned food

Explaining the ancient art of drying food

Understanding the virtue of irradiation

Cold air, hot air, no air, and radioactive rays all can be used to make food safer for longer periods of time by reducing or eliminating damage from exposure to air or to the organisms that live naturally on food.

The methods described in this chapter all have one important thing in common: Used correctly, each process can dramatically lengthen food’s shelf life. The downside? Nothing’s perfect, so you still have to monitor your food to make sure that the preservation treatment has, well, preserved it. The following pages tell you how.

Cold Comfort: Chilling and Freezing

Keeping food cold, sometimes very cold, slows or suspends the activity of microorganisms bent on digesting your food before you do.

Unlike heat, which kills many microorganisms (see Chapter 20), chilling or freezing food may only reduce the population, sidelining them for a while. For example, mold spores (hibernating mold organisms) may sleep inside frozen food like so many bears inside a wintry cave. When spring comes, the bears bounce back to life; thaw the food, and the mold spores do the same.

How long things stay safe in the refrigerator or freezer varies from food to food and to some extent on the packaging (better packaging, longer freezing time). Table 21-1 provides a handy guide to the limits of safe cool storage for fresh food in a refrigerator/freezer maintaining a constant temperature. If these conditions aren’t met, food may spoil more quickly.

Table 21-1 How Long Foods Generally Stay Safe in Cold Storage

Food	Refrigerator (40°F)	Freezer (0°F)
Eggs
Fresh, in shell	3 weeks	Don’t freeze
Raw yolks, whites	2–4 days	1 year
Hard cooked	1 week	Doesn’t freeze well
Liquid pasteurized eggs or egg substitutes, opened	3 days	Doesn’t freeze well
Liquid pasteurized eggs or egg substitutes, unopened	10 days	1 year
Mayonnaise, Commercial
Open jar	2 months	Don’t freeze
TV Dinners, Frozen Casseroles
As originally packed, until ready to serve	Don’t refrigerate: Keep frozen	3–4 months
Deli and Vacuum-Packed Products
Pre-stuffed pork and lamb chops, chicken breasts stuffed with dressing	1 day	Doesn’t freeze well
Store-cooked convenience meals	1–2 days	Doesn’t freeze well
Commercial brand vacuum-packed dinners with USDA seal, unopened	2 weeks	Doesn’t freeze well
Soups and Stews
Vegetable or meat-added	3–4 days	2–3 months
Ground Meats and Stew Meats
Hamburger and stew meats	1–2 days	3–4 months
Ground turkey, veal, pork, lamb, and mixtures of them	1–2 days	3–4 months
Hot Dogs** and Lunch Meats*
Hot dogs, opened	1 week	In freezer wrap, 1–2 months
Hot dogs, unopened	2 weeks	In freezer wrap, 1–2 months
Lunch meats, opened	3–5 days	In freezer wrap, 1–2 months
Lunch meats, unopened	2 weeks	In freezer wrap, 1–2 months
Bacon and Sausage
Bacon*	7 days	1 month
Sausage, raw — pork, beef, turkey	1–2 days	1–2 months
Smoked breakfast links, patties	7 days	1–2 months
Hard sausage — pepperoni, jerky sticks	2–3 weeks	1–2 months
Ham, Corned Beef
Corned beef in pouch with pickling juices*	5–7 days	Drained and wrapped, 1 month
Ham, canned, label says to keep refrigerated	6–9 months	Don’t freeze
Ham, fully cooked — whole	7 days	1–2 months
Ham, fully cooked — half	3–5 days	1–2 months
Ham, fully cooked — slices	3–4 days	1–2 months
Fresh Meat
Steaks — beef	3–5 days	6–12 months
Chops — pork	3–5 days	4–6 months
Chops — lamb	3–5 days	6–9 months
Roast — beef	3–5 days	6–12 months
Roast — lamb	3–5 days	6–9 months
Roasts — pork, veal	3–5 days	4–6 months
Variety meats — tongue, brain, kidneys, liver, heart, chitterlings	1–2 days	3–4 months
Meat Leftovers
Cooked meat and meat dishes	3–4 days	2–3 months
Gravy and broth	1–2 days	2–3 months
Fresh Poultry
Chicken or turkey, whole	1–2 days	1 year
Poultry pieces	1–2 days	2–3 months
Giblets	1–2 days	3–4 months
Cooked Poultry, Leftover
Fried chicken	3–4 days	4 months
Cooked poultry dishes	3–4 days	4–6 months
Poultry pieces, plain	3–4 days	4 months
Poultry pieces covered with broth or gravy	1–2 days	6 months
Chicken nuggets, patties	1–2 days	1–3 months

^*Follow date on package.

^** Caution: Even when food is in date and has been properly refrigerated, always boil or broil hot dogs to an internal temperature of 165°F.

Food Safety and Inspection Service, “A Quick Consumer’s Guide to Safe Food Handling,” Home and Garden Bulletin, No. 248 (U.S. Department of Agriculture, August 1995)

 

Use your common sense: If food seems in any way questionable, throw it out without tasting. This is extremely important because smell alone can’t determine whether a food contains foodborne pathogens. Or as the catchy saying goes: “When in doubt, throw it out.” And for more information on the effects of freezing, go to www.usda.gov, type “freezing food FACs” in the search bar, click, and follow the prompts.

How freezing affects the texture of food

When food freezes, the water inside each cell forms tiny crystals that can tear cell walls. As the food is thawed, the liquid inside the cell leaks out, leaving thawed food dryer than fresh food. The method of freezing (slow versus rapid) affects the amount of drip loss on thawing.

WHAT’S THAT BROWN SPOT ON MY BURGER?

Freezer burn is a dry brownish spot left when moisture evaporates from the surface of frozen food. Because freezer burn changes the composition of fats on the surface of foods such as meat and poultry, it will cause some change in flavor as well.

To prevent freezer burn, wrap food securely in freezer paper or aluminum foil and put the item in a plastic bag. The more air you keep out, the fewer brown spots will develop.

Beef that has been frozen, for example, is noticeably dryer than fresh beef. Dry cheeses, such as cheddar, turn crumbly. Bread dries, too. You can reduce the loss of moisture by thawing the food in its freezer wrap so that it has a chance to reabsorb the moisture that’s still in the package.

Unfortunately, you can’t restore the crispness of vegetables that get their crunch from stiff, high-fiber cell walls. After ice crystals puncture the walls, the vegetable (carrots are a good example) turns mushy. The solution? Remove carrots and other crisp vegetables such as cabbage, before freezing the stew.

Refreezing frozen food

The official word from the U.S. Department of Agriculture is that you can refreeze frozen food — as long as the food still has ice crystals or feels refrigerator-cold to the touch.

The exception may be sauced frozen food, such as frozen macaroni and cheese, because there may be hidden pockets of thawed food where the bacteria are whooping it up as we speak. In other words, partial thaw? Out the door.

Canned Food: Keeping Out Contaminants

Canning (or jarring) food is a three-step heat-dependent process. First, the food is heated, usually in the open container. Second, the container is sealed to keep out air (and microbes). Third, the sealed container is reheated.

Like all heated food, canned food is subject to changes in appearance and nutritional content. Heating food often changes its color and texture (see Chapter 20). It also destroys some vitamin C. But canning and jarring effectively destroy a variety of pathogens and deactivate enzymes that might otherwise cause continued deterioration of the food.

A modern variation on canning is the sealed plastic or aluminum bag known as the retort pouch. Food sealed in the pouch is heated but for a shorter period than that required for canning. As a result, the pouch method does a better job of preserving flavor, appearance, and heat-sensitive vitamin C.

The sealed can or pouch also protects food from deterioration caused by light or air, so the seal must remain intact. If the seal is broken, air seeps into the can or pouch, carrying microbes that can begin to spoil the food.

A more serious hazard associated with canned food is botulism, the potentially fatal form of food poisoning that may result if the food is not heated for a sufficient period of time to a temperature high enough to kill all Clostridium botulinum (or C. botulinum) spores. C. botulinum is an anaerobic (an = without; aerobic = air) organism that thrives in the absence of oxygen, a condition nicely fulfilled by a sealed can. If a low-acid food (such as green beans or peas or potatoes) is incorrectly canned, botulinum spores not destroyed by high heat during the canning process may produce a toxin that can kill by paralyzing muscles, including the heart muscle and the muscles that enable you to breathe.

To avoid potentially hazardous canned food, don’t buy, store, or use any can that is

• Swollen: The swelling suggests that bacteria are growing inside and producing gas.
• Damaged, rusted, or deeply dented along the seam: A break in the can permits air to enter and may promote the growth of organisms other than C. botulinum.

Consumer alert: Never, never, never taste any food from a swollen or damaged can “just to see if it’s all right.” Remember: When in doubt, throw it out.

Yes, Botox is a purified form of C. botulinum. Used correctly, it’s safe — meaning it won’t cause botulinum poisoning.

Dried Food: No Life without Water

Drying protects food by removing the moisture that bacteria, yeasts, and molds need to live.

People have been drying food the low-tech way for centuries by simply putting it out in the sun and waiting for it to dry on its own, the technique used to produce the famous dates of the Arabian desert and the dried meat of the American plains. Drying food the high-tech, modern commercial way means putting food out on racks and employing fans to quick-dry the food at a low temperature under vacuum pressure. At home, a food dehydrator works similar magic.

Spray drying is a method used to dry liquids, such as milk, by blowing the liquids (in very small droplets) into a heated chamber where the droplets dry into a powder that can be reconstituted (made back into a liquid) by adding water. Instant coffee is a spray-dried product. So are instant teas, powdered milk, and all the various instant fruit beverages.

How drying affects food’s nutritional value

As always, exposure to heat and/or air (oxygen) reduces a food’s vitamin C content, so dried foods have less vitamin C than fresh foods.

One good example is the plum versus the prune (a dried plum):

• One fresh, medium-size plum, weighing 66 grams (a bit more than 2 ounces) without the pit, has 6 milligrams vitamin C, 7 to 8 percent of the Recommended Dietary Allowance (RDA) for a healthy adult.
• An equivalent amount of uncooked dried (low-moisture) prunes (66 grams) has only 1.3 milligrams vitamin C.

But wait! Before you leap to the conclusion that fresh is always more nutritious than dried, consider this: Dried fruit has less water than fresh fruit. That means its weight reflects more solid fruit. Although drying destroys some vitamin C, removing water concentrates what’s left, along with other nutrients, jamming more calories, dietary fiber, and/or air-resistant vitamins and minerals into a smaller space.

As a result, dried food often has surprisingly more nutritional bounce to the ounce than fresh food. Once again, consider the plum and the prune:

• A medium-size, pit-free plum weighing slightly more than 2 ounces provides 35 calories, 0.1 milligrams iron, and 670 IU (67 RE) vitamin A. (What’s IU? What’s RE? Check out Chapter 3.)
• Two ounces of uncooked, low-moisture prunes have about 193 calories, 2 milligrams iron, and 952 IU (72 RE) vitamin A. In other words, if you’re trying to lose weight, you need to be aware that although dried fruit is low in fat and rich in nutrients, it’s also high in calories.

When dried fruit may be hazardous to your health

Many fruits, such as apples, contain polyphenoloxidase, an enzyme that darkens the flesh when the fruit is exposed to air. To prevent the fruits from darkening when dried, they’re treated with sulfur compounds known as sulfites. The sulfites — sulfur dioxide, sodium bisulfite, sodium metabisulfite — can cause potentially serious allergic reactions in sensitive individuals. For more about sulfites, see Chapters 22.

Irradiation: A Hot Topic

Irradiation is a technique that exposes food to electron beams or gamma radiation, a high-energy light stronger than the X-rays your doctor uses to make a picture of your insides. Gamma rays are ionizing radiation, the kind of radiation that kills living cells. Ionizing radiation can sterilize food or at least prolong its shelf life by

• Killing microbes and insects on plants (wheat, wheat powder, spices, dry vegetable seasonings)
• Killing disease-causing organisms on pork (Trichinella), poultry (Salmonella), and ground beef (pathogenic E. coli)
• Preventing potatoes from sprouting during storage
• Slowing the rate at which some fruits ripen

Irradiation doesn’t change the way food looks or tastes. It doesn’t change food texture. It doesn’t make food radioactive. It does, however, alter the structure of some chemicals in foods, breaking molecules apart to form new substances called radiolytic products (radio = radiation; lytic = break).

About 90 percent of all compounds identified as radiolytic products (RP) are also found in raw, heated, and/or stored foods that have not been exposed to ionizing radiation. A few compounds, called unique radiolytic products (URPs), are found only in irradiated foods.

For reliable answers to the most commonly asked questions about food irradiation, check out this U.S. Food and Drug Administration Fact Sheet: www.fda.gov/Food/ResourcesForYou/Consumers/ucm261680.htm.

ARE IRRADIATED FOODS HARMFUL?

Food irradiation has been declared safe and effective in controlling microbial food poisoning and preserving food quality by the United States Department of Health and Human Services, the United States Public Health Service, the American Medical Association, the National Association of State Departments of Agriculture, the American Dietetic Association, and the World Health Organization.

Some consumers, however, remain leery of the process, fearful that it may expose them to radiation or that compounds produced only when foods are irradiated may eventually turn out to be harmful.

In fact, irradiated foods don’t emit radiation. But the story of irradiating foods is still unfolding, a situation that makes many people uneasy. For example, the FDA’s 2003 decision to allow irradiated ground beef into the National School Lunch Program has triggered debates in many school districts; several — including Los Angeles and the District of Columbia — have simply banned irradiated foods from their menus.

Around the world, all irradiated food is identified with this international symbol.

Just in case that isn’t enough to get the message across, the package must also carry the words “treated by irradiation” or “treated with irradiation.” The only exceptions are spices and commercially produced food that contains some irradiated ingredients, such as spices. For example, neither the symbol nor the wording is required on the packaging for a frozen pizza that’s seasoned with irradiated oregano. The following table lists the foods approved for irradiation in the United States.

Foods Approved for Irradiation in the U.S.

Food	Approval Date
Wheat, wheat flour	1964
White potatoes	1964
Garlic powder, onion powder, dried spices	1983, 1985
Dried enzyme preparations (such as milk protein clotting enzymes used in making cheese)	1985
Pork	1985
Fruit and vegetables (fresh)	1986
Herbs, herbal teas, spices, vegetable seasonings	1986
Poultry (fresh, frozen)	1990 (FDA), 1992 (USDA)*
Beef, lamb, pork, horsemeat & byproducts	1997 (FDA), 2000 (USDA)*
Ready-to-eat, unrefrigerated meat/poultry products	1999
Fresh eggs (in shell)	2000
Seeds for sprouting	2000
Fruit and vegetable juices	2000
Imported fruits and vegetables	2002
Meat for the National School Lunch program	2002
Fresh spinach and iceberg lettuce	2008
Fresh or frozen mollusks (oysters, clams, mussels, scallops)	2009
Fresh or frozen crustacean (shrimp, crabs, lobster)	2014

* Both the FDA and the USDA must approve treatment of meat and poultry.

Federal Centers for Disease Control; Food and Drug Administration; Food Safety and Inspection Services, U.S. Department of Agriculture, and www.fda.gov/Food/ResourcesForYou/Consumers/ucm261680.htm

IS THAT FOOD STILL GOOD TO EAT?

Understanding the dating terms on food package labels can help you figure out whether the food inside is still safe and tasty — or ready to be discarded. Here’s what the words mean:

• Sell by: The last date on which the food can be offered for sale. Stored properly, most perishable foods like milk and packaged meats are safe for a few days past the sell-by date.
• Best if used by or Use by: Refers to the food’s flavor and quality, not its safety; the manufacturer’s recommendation of the last date on which the food is likely to taste best.
• Expires or Do not use after: The last date on which a product either provides the highest nutritional value or works best (for example, the last date yeast is likely to make bread rise).
• Packing date: Used on eggs from USDA; written as a number from 1 (January 1) to 365 (December 31 — except in a leap year, naturally). Eggs from USDA-inspected plants may also carry an expiration date.