Some foods, like potato chips or frozen dinners, are processed heavily and loaded with preservatives. Their packaging bears a printed date, but the truth is that they are safe to eat far beyond their expiration. These foods use open dating, a system that ensures the product will be at optimum freshness when consumed. Dates labeled 'Best if used by,' 'Best before,' or 'Sell by' aren't expiration dates or concerned with food safety. Instead, they tell you when the food will taste best, which is also a marketing ploy to encourage you to toss "old" unopened bags and buy new ones.

When you look at shelf-stable products and canned foods, you might see a set of numbers and letters. This code uses closed dating, which documents the date and time of production. Manufacturers use closed dating to help with logistics, and grocery stores rely on this system to help them rotate inventory. If it's not an expiration date, it's probably closed dating—which you can take with a grain of salt. For one thing, it will always be in the past, so don't be alarmed.

There are exceptions to every rule—especially sell-by dates. Foods with accurate expiration dates include packaged salads, deli meats, and unpasteurized cheeses. Beyond their expiration, these products can carry pathogenic bacteria that you can't detect by sight or smell alone. You should also pay strict attention to the dates on baby food and cans of infant formula, which are regulated to ensure your baby receives enough nutrition to grow healthy by suggesting the date at which point the food has likely lost some nutritional value.

The expiration date on bottled water is one of life's greatest mysteries, but those numbers aren't telling you what you think. Water doesn't expire, but the bottle it's in may start to decline in quality over time. As the material degrades, it could leach BPAs into the liquid, so it's best consumed before the listed date. Another explanation is that some bottling plants also print dates on all bottles regardless of their contents. This protects the company from claims against the quality of its beverages after a certain date.

There are some foods that, if kept in ideal conditions, will last indefinitely in your pantry. Honey is low in water and high in sugar—two attributes that bacteria don't appreciate. Keep moisture out of the jar and maintain a tight seal to keep honey for a long time. The same goes for uncooked rice and grains, which you should always transfer to an airtight container. Kept in a cool dark place, they can last nearly a decade. Brown rice is an exception; its unsaturated fat content causes it to spoil more quickly.

It's a good rule of thumb to rely on your own senses when inspecting your fridge. Start by looking at your food. Fuzzy spots and discoloration are two signs of mold growth. For canned goods, bulging or rusted cans are a clear indication that their contents are not safe to eat. Next, touch the food. Does it feel wrinkled and mushy like an old apple, or slimy like mushrooms gone bad? Lastly, smell the food and discard anything with a rancid, stale, or sour aroma.

Bakers know that packages of yeast always come with an expiration date, but you can still use it in some of your favorite recipes after it's passed. The date on dry active yeast packets is the best guess as to how long the yeast will remain active, but it could start to deteriorate at any time before or after its threshold. Always proof your yeast with a teaspoon of sugar in 1/4 cup of warm water before baking. It should rise to about double its size with a foamy surface. If it doesn't, it's expired, and it won't do its job in your bread.

Some food items can spoil before the printed date if you don't handle them properly. Leaving food out on the counter for too long or setting your refrigerator to the wrong temperature are two habits that shorten the shelf life of your groceries. Refreezing meat and poultry is okay if you thawed the meat safely. Thawing meat at room temperature encourages bacterial growth on its surface, which can survive another round in the freezer, so always opt for a fridge thaw.

It's not a risky move to snack on stale sunflower seeds or use old bread for French toast. Some food items, however, are best sent to the garbage bin if you have any doubts. Fresh meats, for example, shouldn't sit in your fridge longer than a few days—either eat or freeze them to keep them from going rancid. Also, foods like hot dogs could spoil before the printed date if they are open for more than four or five days. Trust your senses, and toss anything that seems suspect, regardless of the date.

The U.S. Department of Agriculture website is a great resource for food safety information. Founded by President Abraham Lincoln, the USDA and the Food Safety and Inspection Service work together to ensure food safety and humane animal handling. Here, you'll find information about expiration dates, proper food handling and preparation, and ongoing product recalls.