How to Tell If an Onion Is Bad

Onions are essential aromatics and one of the most important veggies to have around in the kitchen. They're even the third most consumed fresh vegetable in the U.S., according to the National Onion Association. Yes, the NOA is real – that's not made up.

Because they're such important staples for cooking and for cold uses like salads and sandwich toppings, people try to keep them on hand and often buy them in bulk. Still, you don't always get through a 3- or 5-pound sack as quickly as you expect. This might leave you wondering about onion shelf life and proper storage, not to mention how to identify a bad onion.

It's a question with which every home cook must grapple at some point. Here are some questions to help you decide:

• Is there mold growing on the onion?
• Does the onion have any discolored areas? 
• Is the onion giving off an unpleasant odor?
• Is the onion soft or downright squishy?
• Are there soft spots on the onion?
• Is the onion's flesh all dried out?
• Has the onion started sprouting?

If you answer "yes" to one or more of these questions, toss the onion. However, for one caveat, a newly sprouting onion with none of these other problems is still OK. Just use it soon, as onions start rotting quickly once they begin sprouting.

The ideal storage temperature for whole, unpeeled raw onions falls between 40 and 50 degrees Fahrenheit. That's not particularly convenient since it's warmer than the refrigerator and cooler than room temperature. They need a cool, dry, dark place. If you have a basement, cellar, garage or shed that's cooler than the house and doesn't get humid, that's a good spot.

Don't keep unpeeled onions in the fridge, as it's too cold and humid. If their dry skins absorb moisture, it accelerates the spoiling process and fosters bacteria and mold growth. Store them in something that lets them breathe well, like a hanging wire basket or a netted or mesh bag, and never store them in a plastic bag or sealed container. Because they need a well-ventilated area, the pantry isn't a great choice.

Store peeled whole or cut onions in the fridge. To maximize their life, keep them in an airtight container or tightly sealed plastic bag. Peeled and cut onions can also be frozen to prolong their life. For the best results, vacuum seal them or press as much air as you can out of the freezer bag you use. Cooked onions should be refrigerated in a sealed container or bag and can also be frozen.

Whole, unpeeled onion shelf life varies depending on how well they're stored. Under ideal conditions, they'll easily last for one to two months. At room temperature but with plenty of fresh air circulation, it's often closer to the shorter end of that window.

Whole, peeled onions generally hold up for about two weeks in the fridge, while refrigerated cut onions should be used within seven to 10 days, and raw, peeled frozen onions are best used within about six months. Cooked onions last three to five days in the fridge, and if they're frozen, eat them within three months for the best quality.

Selecting the best onions at the time of purchase is useful for getting onions that last the longest and that don't prompt questions about whether they're bad shortly after you bring them home.

Choose onions that are firm, free of soft spots and that feel heavy for their size. They should be fully wrapped in their skin, which should be papery and dry. Don't pick any onions that have mold, discoloration, bruises, cuts or any other signs of damage. Be aware of any rotten onion smells. Raw, unpeeled onions shouldn't really have a detectable smell. Sprouting onions go bad quickly, so avoid them.