By Chanie Kirschner, Mother Nature Network
It's important to know when companies use an actual expiration date on items or a sell-by date. Often, the date printed on the package is the sell-by date, so for many items, it's safe to use things after that time. But for how long exactly?
The FDA points out that when a "sell-by" date is marked on an item, it is simply an indicator for stores to know how long to display something. Alternatively, some things may have a "best if used by" date - that date indicates when an item will pass its peak quality. You can still use the item after that date if stored properly. Finally, some food items will have an actual "use by" date - these food items should be used by the date on the package.
So, for example, let's take an item like eggs. Eggs are not federally required to have a sell-by or expiration date on them, but some states require it. All eggs that are graded by the USDA have to have a pack date on them, however. This date is written as a three digit number, representing the day of the year they were packed. For example, if the number is written "078," then that date would be March 18, 78 days from Jan. 1.
Related: Uses for leftover egg yolk
According to the FDA, eggs are still good for three to five weeks after you purchase them, as long as they're stored properly in the coldest part of your refrigerator (i.e. not on the door). Even though the expiration date may pass during this time, they are still OK to use.
What about dairy items, like yogurt and cheese? Yogurt will usually be good for a couple of weeks after the expiration date, as long as it's unopened. Once it's opened, though, you should use it within a week. And cheese (though it may seem like it can last forever) also has an expiration date. Hard cheeses should be used within three weeks after opening, but can last up to six months in the freezer. (I buy those big packages of shredded mozzarella from Costco and keep them in the freezer for that emergency baked ziti that needs to be made when there is nothing else in the house besides noodles, pasta sauce, and - you guessed it - cheese.)
Related: 9 ways to use up leftover macaroni and cheese
You asked about cake mix. A story that circulated through my email inbox a few years ago reported a 19-year-old college student died from eating old pancake mix. Snopes.com found the warnings to be far-fetched, but somewhat warranted, if you happen to be allergic to mold. Pillsbury website says to refrain from using cake mixes that have expired, because of potential changes to taste, color and texture. I say, when in doubt - throw it out. (But then again, that's my motto for pretty much everything.)
For more info about the shelf (or refrigerator) life of meat and dairy products and to find out more about product dating, check out the FDA's food product dating page.