Shelf Life of Foods: What You Need to Know

Despite the fact that the name of this site is Shelf Life Advice, it's impossible to guarantee that the shelf life information we give you will accurately predict how long a particular edible item will last in your home. And despite the fact that many of your food purchases have a use-by date stamped on them, the food is likely to seem just fine to you for days or even weeks after that date. We asked the scientists on our site's Advisory Board to enlighten us about shelf life and use-by dates by answering the questions below. 

Note: While reading this piece, keep in mind that use-by dates are about spoilage, not contamination. They tell you when the food will begin to deteriorate in one or more of these ways: taste, scent, and/or appearance/texture.  They are not about the growth of pathogens that could make you sick. Most foods will be fine for several days, and perhaps a few weeks after that date.  Some last much longer, for example, some nonperishables such as dry cereal.  Another reminder: don't confuse use-by and sell-by dates. Egg cartons commonly have only sell-by dates; the eggs are fine for 3-5 weeks after that date.

What's the relationship between shelf life and the use-by date on a product?

Food scientist Dr. Clair Hicks provided these explanations:

• "Best- if-used-by dates should be about 2/3 of the shelf life of a retail food.  This is what good manufacturers do.  They never want a consumer to have a bad product.
• Food scientists set the shelf life of the food by how soon the fastest problem occurs.  If it's a fresh food that has a micro problem, then the shelf life is short.  If it's a hermetically-sealed package that has been retorted [sterilized], then the shelf life is quite long." 

Do people disagree about whether a food is spoiled or not?

They sure do. At least, my husband and I sure do. Expired milk that tastes fine to him tastes sour to me.  Baked goods that taste stale to me taste fine to him. Food process engineer Dr. Timothy Bowser put it this way: "Shelf life is definitely not a one-size-fits-all issue." He gave this example: "Many people eat a very soft banana and enjoy it while others turn away in disgust."

Dr. Bowser also commented upon spoilage versus contamination: "Shelf life is so much more than food safety!  Safety is probably the most important issue, but, in countries where food is plentiful, it often takes a back seat to appearance, convenience, and taste."

Do locally-sourced products (perhaps purchased at a farmers' market) last longer than products purchased at a supermarket?  And are they less likely to be contaminated?

"Many people think that locally-sourced foods have a longer shelf life because they're fresher," food scientist Dr. Karin Allen says. Yes, they may have been picked or baked a day or two before you bought them. However, our Board scientists agree that this does not mean they have a longer shelf life than comparable supermarket items. Locally-sourced foods may taste better soon after you purchase them, but it's a good idea to consume them within a few days after purchase.  Three of our site's Board scientists explain why. 

Dr. Hicks' comments may surprise you:

• "I'm not sure that locally grown is much of an advantage for shelf life.  Locally grown foods are usually more tasty because they were picked when they became ripe (not earlier).  However, locally-grown food deteriorates a bit faster because of the sugar content in fully ripe produce. Furthermore, produce is not washed in the same sanitary manner and then coated with wax or oil and refrigerated, as products handled by big companies are. These procedures increase shelf life dramatically. 
• The temperature and atmosphere used in commercial systems can keep fruits and vegetables looking great for extended period.  The potatoes and onions that we buy in April were last year's, but they have been stored in refrigerated storage under a defined gas mixture.  They are only taken out of this condition when they are moved to retail. 
• When the product goes to retail the special atmosphere is lost and the refrigeration temperature general goes up, so shelf life becomes limited. Once a refrigerated product comes into the home, dehydration of fruits and vegetables often determines the shelf life of the product. When the consumer gets these products, they only have a couple of good weeks before they sprout or degrade from bruises on the skin. When the product doesn't look right, the consumer tosses it." 

Dr. Bowser points out that local doesn't mean either longer shelf life or greater resistance to contamination:

• "Locally-sourced food is not always the best!  A free-range chicken, for example, may be a carrier of more bacteria than a chicken from one of the big producers.  The free-range chicken may be exposed to a less-controlled environment and could have access to the bacteria living in the feces of wild animals (a great place to look for bugs if you are a chicken).
• "Local slaughter houses don't always have the resources of the big processors; consequently, the local houses may not function as well as the big processors.  Carcass cooling is one example: the big processors use continuous-belt ammonia refrigeration systems for rapid chilling.  A local processor is much less likely to have this resource and may rely on a home-style chest freezer or chipped ice.  The big processor probably employs a team of microbiologists, a dedicated cleanup crew, a continuous improvement group, and a host of internal and external inspectors. The local processor probably has few, if any, of these professional resources available."

Food scientist Dr. Catherine Cutter says that, from her personal experience, food purchased at farmers' markets don't have as long a shelf life as food from supermarkets.  Why not? "Farmers' markets food may not have the preservatives or special storage conditions such as gas chambers that keep ethylene out."

What mistakes do consumers make that can cause food to become contaminated or spoil faster than expected?

Dr. Hicks points this out: "Once the consumer gets the product and opens it all bets are off as to the shelf life.  Some people drink out of the carton or eat a portion of the food out of the container and contaminate the food by reinserting a used utensil. Once these abuses occur, the shelf life can become rather short. I have also known people to leave milk out for a half day and wonder why it went bad the next day." 

Temperature abuse (for example, keeping perishables out of the fridge for more than 2 hours) can hasten spoilage and cause contamination.  Cross-contamination (for example, putting cooked meat on the same unwashed plate that once held the meat when raw) can cause contamination that can lead to illness.  These are two very common mistakes that home chefs make. 

How can the refrigerator shorten or lengthen shelf life?

Here are important matters to remember about refrigeration:  The fridge must be at the correct temperature (between 35°F - 40°F).  Colder temperatures will extend the shelf life of some foods but may freeze lettuce and berries and create clumps of ice in beverages.  Too warm will cause faster spoilage and perhaps contamination. There should be a thermometer in the fridge to keep track of the temperature.  If there is no built-in thermometer, buy one; it's a small investment. Note: an overloaded refrigerator may not be able to keep food cool enough. The cool air needs room to circulate.

Ignoring spills in the refrigerator or forgetting to clean and sanitize the entire interior regularly can shorten the shelf life of the foods stored in it. For tips on proper cleaning, go to "How to Clean the Refrigerator." 

Dr. Cutter adds these suggestions:

• Try not to open the refrigerator very often or hold it open for a long time.  That makes cool air rush out and warm air rush in.
• Don't put a large container of hot or very warm leftovers in the fridge. Place the food into 2 or perhaps even 3 shallow pans and cool them further by placing each container into an ice bath (a larger container with water and ice cubes) before refrigerating.
• Place raw meat in the back of the bottom shelf, where the fridge is coolest and where the meat can't drip on other foods.
• Don't crowd your fridge with foods that don't need to be refrigerated.

You can avoid over-packing your refrigerator by removing foods that really don't need to be in there.   To find out which foods can be removed and why, check out "15 commonly refrigerated foods that don't need to be."  Here are some foods the article says will last longer and/or taste better if not refrigerated: bread, honey, coffee, tomatoes, and potatoes. These you have a choice about: onions, garlic, butter, and condiments.  What about eggs?  Europeans don't need to refrigerate them, but in the U.S. eggs are processed differently and are at higher risk of developing salmonella if not refrigerated.

Can improper wrapping and storage of a product shorten its shelf life?

Absolutely. The way consumers handle food products has a lot to do with how long they last. This includes how foods are wrapped for refrigeration or for freezing. Double wrapping or using the heavier plastic bags labeled for freezing give more protection from freezer burn.  Where foods are stored can also affect shelf stable products.  For example, canned goods shouldn't be placed next to the oven. Spices will last longer if placed in a dark cabinet rather than where they're exposed to sunlight.  

Shelf Life Advice contains a lot of information about proper wrapping and storage.  There's general advice about types of foods (such as produce) in the Tips and FAQ sections) as well as specific information on particular foods in the site's Product sections.  Here are 2 links to advice on wrapping and storage.

"Everything You Need to Know about Wrapping Foods Right" (This article contains several links to information about wrapping specific foods and types of foods.)

Produce Storage Tips (Scroll down a few pages in Live Well Utah to reach this handy chart created by Dr. Karin Allen, one of the Shelf Life Advice Advisory Board members.)

For more information on storage and wrapping, use the search box on the home page. 

Source(s):

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 Nettles Cutter, Ph.D., Pennsylvania State University, Department of Food Science

Clair L. Hicks, Ph.D., University of Kentucky, Dept. of Animal and Food Sciences

www.mnn.com "15 commonly refrigerated foods that don't need to be" 

http://www.mnn.com/food/healthy-eating/stories/15-commonly-refrigerated-foods-that-dont-need-to-be

ShelfLifeAdvice.com "Should Hot Food Go into the Fridge?" 

http://shelflifeadvice.com/content/should-hot-food-go-fridge