- Meat and Poultry
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- What are bacteria?
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- How many types of bacteria are there?
- What foods are likely to be contaminated by listeria?
- What foods can give a person a staph infection?
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- Why do some bacteria make people sick?
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- Exactly what is meant by the phrase perishable food?
- Defining Some Current Language about Food
- What Does the Word “Foodie” Mean? It Depends Who(m) You Ask
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- What does the term shelf life mean?
- What's in Our Food? Maybe Processing Aids, Maybe not
- “Fresh,” “Natural,” “Processed”—What Do These Words Mean?
- FAQs on Dropped Food
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- Exactly what defines a farmers’ market?
- Farmers' Markets: Why They're So Popular; How to Find One Near Your Home
- How should I handle produce at home?
- What foods are sold with restrictions at a farmers’ market?
- What should I bring to the farmers’ market?
- What shouldn’t I do or eat at a farmers’ market?
- What signs indicate a sanitary farmers’ market?
- What time of day is it best to go to a farmers’ market?
- FAQs on Food-borne Illness and Mishandling of Food
- About how many cases of food-borne illness occur in the U.S. each year?
- Answer Key to “How Much Do You Know about Safe Handling of Food?”
- How Much Do You Know about Safe Handling of Food?
- I Left It Out Too Long! Can I Still Eat It?
- Should Your Grocery Card Track Food-Borne Illnesses?
- Sudden, Awful Intestinal Distress--Is it the Flu or a Foodborne Illness--or Both?
- What YOU Can Do to Avoid Food-borne Illness
- What does the phrase food-borne illness refer to?
- FAQs on Food Product Dating
- Are stores required, by law, to remove outdated items from their shelves?
- Do most consumers actually pay attention to the dating on foods?
- Does the “use by” date matter once the product is frozen?
- Is information on food longevity and safety available by phone?
- What are expiration dates?
- What do the terms closed dating and open dating mean?
- What if there is no date on a product, and I don’t remember if I bought it a month ago or ten years ago?
- What should consumers know about food product dating?
- When Did You Buy It? When Did You Open It?
- When to Throw Food Out? Not on the Use-By Date
- Who establishes these product dates?
- Who requires and regulates dating on foods?
- Why do “best by” and “use by” dates sometimes seem conservative?
- FAQs on Food Safety
- "Is It Safe To….?" FAQs Answered by our Advisory Board
- FAQs about Ground Beef, Seasonings, Olive Oil, Lemon Wedges, and Fish
- FAQs about Mushrooms: Are they Very Dirty or Very Clean?
- FAQs about Soft Cheeses--What's Safe, What Isn't
- FAQs on Food Safety and Nutrition
- FAQs on Raw Fruits and Veggies—the Answers Can Protect Your Wallet and Your Health
- Food/Meat Thermometers—What You Need to Know
- How Long Should Cheese Be Aged? Will the Rules Be Changed?
- How Long Will They REALLY Last? Part I: Non-perishables
- How Long Will They REALLY last? Part II: Perishables
- Imported Foods—What’s Safe, What’s Risky?
- Is It Safe? Is It Nutritious? More Survey Answers from Scientists
- Is It Time to Switch to Pasteurized Eggs?
- Is the Food Safety Modernization Act Making Our Food Supply Safer?
- More FAQs about Minimum Safe Cooking Temperatures: Pork and Other Perishables
- Sushi: Why Such a Short Shelf Life?
- Winter Food Storage—Can I leave It in the Car or in the Garage?
- Would You—Should You—Do You--Eat Irradiated Food?
- FAQs on Food Wrapping
- Are any plastic wraps or containers really “microwave safe”?
- Are some plastic wraps more effective than others?
- Can I refrigerate meat and poultry in its store wrapping?
- Can I use plastic freezer bags to store produce in the fridge?
- Can chemicals leach unto food from plastic wrap or containers?
- Do coated plastic bags really help produce last longer?
- Does aluminum foil give foods a metallic taste?
- Does exposure to aluminum cause Alzheimer’s disease?
- Everything You Need to Know about Wrapping Food Right
- How should fruits be wrapped before refrigeration?
- Is it safe to use aluminum foil in a microwave oven?
- Should I wrap raw vegetables loosely or tightly before refrigerating?
- What are some advantages and disadvantages of aluminum foil?
- What produce needs to be wrapped before refrigerating?
- What’s better for wrapping food—plastic or aluminum foil?
- Why does foil sometimes darken, discolor, and leave black specks on food?
- Will a foil cover help keep foods on the table hot or cold?
- FAQs on Freezing Food
- FAQs on Leftovers
- FAQs on Mold
- What is mold?
- Does mold ever grow on nonperishable food?
- Can I remove a moldy part from food and eat the rest?
- About how many different kinds of molds are there?
- How can I avoid getting mold on my refrigerated food?
- Is mold always visible?
- Are any molds harmless?
- What food groups are most susceptible to mold?
- What kinds of illnesses can result from eating moldy food?
- What kind of packaging protects foods from mold?
- What other safety tips will help prevent mold from growing?
- Why are some molds dangerous?
- FAQs on Organic Food
- What Is Organic Food?
- Are Organic Methods More Humane to Animals?
- Does Conventional Food Have a Longer Shelf Life Than Organic?
- Does Organic Food Taste Better than Conventional Food?
- Is Organic Food More Nutritious Than Conventional Food?
- Is Organically Grown Food Better for the Environment?
- What Do the Various Organic Labels Mean?
- What Important Contributions Has the Organic Movement Made?
- Which Are Safer: Organic or Conventional Food Products?
- Will Organic Baby Food Make Baby Healthier?
- FAQs on Oxidation: How It Affects Foods
- FAQs about Plastic Products Used with Food
- Pyrex® Glassware: Is it safe to use?
- Are plastic bags safe to use in the microwave?
- Are some plastic wraps safer and/or more effective than others?
- Are there any health risks from reusing plastic water bottles by refilling them with tap water?
- Are we eating chemicals from plastics along with our food?
- Can I microwave food in my plastic containers?
- Does the plastic used in water bottles pose a health risk?
- If I heat food in an open can, will that cause the plastic lining to leach chemicals into the food?
- Is it safe to heat frozen entrées in their plastic containers and with their plastic wrap?
- Is it safe to use plastic wrap as a covering when microwaving food?
- Is it safe to wash and dry plastic plates, cups, containers, and utensils in the dishwasher?
- Is there good evidence that BPA is harmful to human health?
- Of the plastic products used to store, heat, or eat with (wraps, bags, containers, silverware, plates, etc.), which contain BPA?
- What is BPA?
- Why is so much of today’s food packaged in plastic?
- FAQs on Preservatives
- What are Preservatives?
- All things considered, is our food supply safer or less safe because of preservatives?
- Are the preservatives in hot dogs and similar products health risks?
- What preservatives are known to cause allergic reactions?
- What are some common preservatives used in food?
- What food groups commonly have preservatives in them?
- Why are preservatives added to food?
- Will the label on the product tell me if it contains a preservative?
- FAQs on Washing Produce: Why and How
- Other FAQs
- Can chicken soup really cure a cold?
- Is Chocolate Good For You?
- Can Science and Technology Help You Save Food Dollars?
- FAQs Answered By Our Board Scientists: on Chickens, Bananas, Old Salad Dressing, and More
- FAQs about Food Price Increases
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- FAQs about Shelf Life: Tortillas, Pancakes, Wine, and More
- Food Fraud: Are you paying for scallops and getting shark meat?
- Is Cheese Addictive? Only If You Eat It
- Missing Chickens: Where Have All the Small Ones Gone?
- Nine FAQs about Food Labels
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- Some Shelf Life Info, General and Specific (Spirits, Defrosted Veggies, Green Tea, and More)
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- Ten FAQs about the Prickly Pineapple
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- What’s in My Water? Answers to FAQs
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- Books: Food for Thought
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- Ten Tips for Consumer Food Safety
- Food Allergies: Recognizing and Controlling Them
- “Is It Spoiled?” When in Doubt, Check It Out
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- Recent Recalls: Salmonella Threatens 100s of Products
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- Why You Need a Safe Cooking Temperature Chart and How to Get One Right Now
- “Myth-information” about Food Safety: You’d Better Not Believe It
- After The Storm: What You Can Save and What You Must Throw Out
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- Organic Food, GMOs, the Safety of American Food, the Value of Use-By Dates, and More--Scientists Tell Us What They Think
- Raw chicken, Leftovers, Deli Meats, and More-- What Surveyed Scientists Said
- Tips About 4 Popular Beverages: Wine, Coffee, Water, and Soda
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- Going Away for All or Part of the Winter? Prepare Your Kitchen for your Absence
- How To Grill Safely During the Summer
- How do summer squash and winter squash differ?
- New Year’s Resolutions For a Safer Kitchen
- Preserve the Taste of Summer by Canning—But Do It Safely
- Summer Food Fests Offer Much More than Calories
- Summer Party Tips: Baby Carrots (Using for Dips) Hot Dogs (Ditching the Guilt), and Watermelon (Finding a Ripe One)
- Tailgating: How to Do It Right
- Tips on Keeping Your Summer Fruits Flavorful and Healthy
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- Refreezing Frozen Foods
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How Long Will They REALLY last? Part II: Perishables
Perishable foods--the ones kept in the fridge--are the ones consumers are most afraid of. They worry that expired perishables might make them sick. It's an almost wasted worry. In general, refrigeration keeps bacteria from growing to sufficient numbers to cause illness. Moreover, the bacteria scientists call "spoilage bacteria"--the ones that ruin the taste, looks, texture, and/or smell of food--grow faster than those that cause illness, so food usually turns yucky and gets discarded before it becomes a menace.
Food-borne illness is not generally caused by eating old food; most of the time, it's caused by cross-contamination or by foods that have been kept for at the wrong temperature--not hot enough or cold enough. Scientists refer to this as temperature abuse. Perishable foods kept in the "danger zone" (40°F - 140°F) allow bacteria to grow rapidly to a level that can cause illness. (For an elaboration of these points, click here.)
"Can I Eat It?" General Guidelines
Refrigerated foods will, of course, spoil eventually. How can you tell when? Food scientist Dr. Susan Brewer says that, to some extent, you can rely upon your senses. If a refrigerated food looks, smells, and feels okay (that is, it's doesn't feel slimy), it is probably safe to eat for 4-7 days after the "use-by" date, although it may not taste as good as it did prior to its expiration.
The guidelines for keeping leftovers are usually given at about 3-4 days, but some foods last a little longer. For more information about how long to keep specific leftovers, click here.
You may have noticed that perishable foods typically have a "sell-by" or "best-by" date (as opposed to the "use by" or "best by" date on a shelf-stable product.) You can assume that a "sell-by" date gives you at least a few more days of high quality.
Ever wonder what happens to food that makes it spoil? Food scientist Dr. Karin Allen lists the damaging effects in three categories: physical changes, chemical reactions, and microbiological changes. Let's see what happens in each of these categories.
Separation: Examples are an oil layer in salad dressings and solids settling to the bottom of liquids.
Losing water or becoming stale: These changes can affect baked goods, pudding, gravy, and vegetables (causing veggies to wilt).
Oxidation: This can cause rancidity in oils, a cardboard flavor in milk, and the browning of red meat.
Enzymatic reactions: These can cause the browning of cut fruits, a softening of fruits, and nutrition loss.
Spoilage: In fruit, spoilage may be caused by yeast and molds. In vegetables, it may be caused by bacteria and molds.
Microbial enzymes: These cause fermentation.
Safety issues: These can result from improper storage of minimally processed foods. There are also safety issues involving deli meats and cheeses, which are discussed later in this article.
Specific Food Groups
Fresh fruits and vegetables:
Many fresh fruits and vegetables are not given a "sell-by" or "use-by" date. Visual condition is commonly used as a guideline. For example, if bagged lettuce (which usually is dated) has been kept in the fridge and continues to look fresh, it will be safe to eat.
The general guideline for dairy products is that quality will remain high for 7 days after the "sell-by" date. Changes that occur in these products are usually a matter of chemical reaction not bacteria.
MILK: Spoilage bacteria may cause souring, which is not unhealthy to consume.
YOGURT AND SOUR CREAM: These products are already fermented. Whenever fermentation (with yeast, mold, or certain types of bacteria) is controlled so that one is allowed to grow, it will outcompete harmful bacteria, and the product will have a relatively long shelf life. However, if yogurt or sour cream develop mold, discard the entire container.
CHEESE: Cheeses are also already fermented. They are most often spoiled by molding. If a fresh or soft cheese looks moldy, discard all of it. Dangerous spores may have spread throughout the cheese. Mold in a hard cheese can be cut away (cut off about an inch from the mold) and the rest of the piece safely consumed.
Soft cheeses, especially those unpasteurized and not aged, should be discarded by the "use-by" date. These cheeses can become contaminated easily and cause illness.
BUTTER: Food process engineer Dr. Tim Bowser says he considers butter a shelf-stable product. It does not need refrigeration, which is why some restaurants leave it out on the table for customer after customer. However, at home, most people keep butter in the fridge because that prolongs its shelf life.
ICE CREAM: Sometimes ice cream doesn't even hold up as long as the manufacturer's expiration date promises. Ice cream can get gummy or dry out. I put ice cream in a freezer-strength plastic bag to give it a little more protection. Before serving ice cream you've had for awhile, taste a little to see if it still tastes good.
EGGS: Uncooked, refrigerated eggs can be used 3-5 weeks after the "use-by" date. Hard-boiled eggs, if refrigerated, will last a week.
Here are some tips from food scientist Dr. Karin Allen:
- Catsup, hot sauces, and barbecue sauces contain preservatives that prevent mold or yeast growth.
- The following should be refrigerated after opening and checked for mold after a couple of weeks: salsas, tartar sauce, and creamy condiments. If mold is found, discard the entire jar.
- Mustard and horseradish are natural preservatives. However, they can lose flavor as a result of oxidation.
Raw meat, poultry, and fish:
These foods will taste best if you follow the date suggested on the packaged products or either use them or freeze them within a few days. If you're buying directly from a butcher and the product isn't dated, ask how long you can keep the raw item. All of these foods should be wrapped tightly when refrigerated. The packaging from the store is usually fine. If the item is going uncooked into your freezer, ask or it to be freezer-wrapped.
Deli meats and hot dogs:
Many consumers have the mistaken idea that deli meats can last almost forever because they have a lot of preservatives in them. However, they are actually quite susceptible to contamination and spoilage. Therefore, they have a short shelf life unless frozen. Deli meats can be contaminated by listeria or by staph, either of which can cause serious illness. Also, spoilage bacteria can grow on these and cause them to become "slimy."
Unopened deli meats can be consumed up to the "use-by" date. Once the package is opened, they should be eaten or discarded within 3-5 days, as should luncheon meats purchased from a deli counter. Food scientist Dr. Catherine Cutter advises buying these products pre-packaged rather than from a deli counter. Meats bought there can be contaminated by unsanitary handling by employees, by a slicer not adequately cleaned, or by cross-contamination from another product sliced on the same machine. A store slicer should be cleaned every two hours, but the consumer has no way of knowing if a store is actually following that safety procedure.
Furthermore, Cutter points out that pre-sliced deli-counter meats have a lot of surfaces exposed to air, and are, therefore, likely to spoil faster than the pre-packaged slices. Buy these, she suggests, only if you're going to use them within a day or two.
Be sure your hot dogs are cooked well (to 165°F), and don't keep them forever in your fridge. Pay attention to the use-by date. Even an unopened package should be discarded once that "use-by" date comes. According to FoodSafety.gov, if there is no product date on the package, unopened hot dogs can be safely stored in the fridge for two weeks. Once opened, keep them only one week. If you open the package, use some, and don't plan to use the rest within a week, freeze the remainder, wrapped well in a freezer-wrap plastic bag. They taste just fine when boiled from the frozen state. For maximum quality, keep frozen hot dogs no longer than 1 or 2 months.
To reach links to additional Shelf Life Advice articles and Q/As about proper handling and health risks of deli meats and hot dogs, just type "deli-meats" or "hot dogs" into the search box on the home page.
To cool foods properly and avoid rapid bacterial growth, keep your fridge sufficiently cold, uncrowded, and clean. Here are a few tips on refrigerator care:
- Your fridge should be no warmer than 40°F, but you can keep it cooler than that. Cooler will extend the shelf life of many foods. Try 35-38°F. But check to be sure you aren't getting ice crystals in you milk or freezing the lettuce. (Frozen lettuce is ruined.)
- Don't stuff your fridge to the gills. For a refrigerator to cool properly, there must be space for the air to circulate. Get rid of old leftovers to make room for newer items.
- Don't put a large container or quantity of hot food in the fridge in one space. It may take several hours to cool, and, by that time, bacteria have had a feast on it, and your chili, casserole, or whatever may be ruined or even contaminated. Divide hot food into smaller amounts, or put containers of hot leftovers into an ice bath and cool them down before refrigeration.
- Keep your fridge clean! Bacteria love spills, so wipe these up promptly. Periodically, take everything out of the fridge and clean and sanitize it. How often? We recommend once a month, more often if it smells bad or looks unclean. For more tips on proper refrigerator care, click here.
- Proper wrapping of perishables will lengthen shelf life. Shelf Life Advice has a few articles on this topic. Here are the links to these:
If you put "wrapping" into the search box on the home page, you'll find links to Q/As and articles about specific foods and specific products for storing food (plastic containers, aluminum wrap, fish, etc.)
Foods that were not contaminated when they went into your freezer will remain safe forever. BUT that doesn't mean you can keep them forever. Quality deteriorates over a long period of time, especially if they are not wrapped well. Furthermore, says food scientist Dr. Joe Regenstein, if oxidation gets bad enough, some scientists believe the food can become unhealthy. For tips on wrapping for the freezer, click here: http://shelflifeadvice.com/tips/how-wrap-foods-freezer
Food scientist Dr. Karin Allen says that freezer burn is the main reason frozen food deteriorates. But freezer burn does not necessarily mean the food must be discarded. Here are Allen's suggestions if your frozen food develops freezer burn:
1) Discard thin cuts or deli slices.
2) Use freezer-burned ground meats or sausage in dishes that are heavily spiced, such as chili.
3) Roasts can be thawed in the fridge. Then, freezer-burned sections can be trimmed away.
Here's what Dr. Regenstein says about freezer burn and techniques for avoiding it: "Everything is subject to freezer burn. The more 'water' in the product, the more likely there will be freezer burn. The key to prevention is TIGHT wrapping. If 'oxidation' is a problem, then putting certain foods in water will help prevent that. Food processors can do this with a process called 'glazing.' The product is usually frozen and then dipped into a glazing solution-- often it's plain water but other times processors may add a few other compounds, such as gums, to make the solution more viscous. This then freezes on the surface. Sometimes, water is added prior to freezing, for example, with shrimp and some fruits."
Give a little thought to what you store in the freezer door, especially if your household includes folks who frequently open the freezer looking for ice cream or just browsing through the frozen meal choices. Dr. Bowser keeps these items in or near his freezer door: ice cubes, freezer packs, nuts, flour, cereal, and other low-moisture foods. What does Dr. Regenstein keep in his freezer door? Batteries, coffee, and other items that don't have freezer-burn considerations.
Between perishable and non-perishable foods, there is a third category called "semi-perishable." Here's how the USDA defines this group: "The category of semi-perishable foods can encompass a wide variety of foodstuffs that have varying shelf lives. Generally, semi-perishables require no refrigeration and are shelf stable, except under extreme temperatures, due to the presence of preservatives, specialized processing or packaging. Examples include dried fruit, ultra high temperature treated milk and pasteurized fruit juices in aseptic packaging." To this list, Dr. Allen adds most hard cheeses, such as cheddar and Parmesan. "They're better if refrigerated," she says, "but still safe if they haven't been."
To read about the shelf life of non-perishables, click here:
Karin E. Allen, Ph.D., Utah State University, Dept. of Nutrition, Dietetics, and Food Sciences
Timothy J. Bowser, Ph.D., Oklahoma State University, Dept. of Biosystems and Agricultural Engineering
Catherine N. Cutter, Ph.D., Pennsylvania State University, Dept. of Food Science
Joe Regenstein, Ph.D., Cornell University, Dept. of Food Science
Susan Brewer, Ph.D., R.D. University of Illinois, Department of Food Safety and Human Nutrition
FoodSafety.gov "Tips for Tailgating: Hot Dog Safety Basics"
fas.usda.gov "Report to Congress on Use of Perishable Commodities and Live Animals in Food Aid Programs, III. A. "Perishable and Semi-perishable Commodities"
Links to additional sources within this website are provided in the article.