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Ways to Tell If an Onion Is Bad

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Onions are versatile and flavorful. You can use them in salads, sandwiches, soups, baked goods, and more. When shopping for groceries, onions are something many people buy in bulk. You always want to have onions on hand because you might need them at any time.  

However, sometimes you may end up with onions from over a month ago, whether raw or cooked. Are they still good to use at that point?

How do you tell if an onion is bad?  

You can tell an onion is bad if it starts being mushy, has dark spots, or starts to sprout.  

Our detailed guide covers how long onions last. We also list some more ways you can tell that an onion is going bad.

How Long Do Onions Last?

Understanding how long onions last will help you determine when they are close to spoiling.  Here’s a breakdown of how long onions last when raw, cut, or cooked.  

  • Raw – Raw, whole onions can last for up to two months when stored properly.  
  • Cut – Cut onions can only last for seven days. Ensure that the cut side is wrapped before being stored in the fridge. The cut should be facing down when stored. Avoid wrapping cut or sliced onions in plastic wrap, and instead, opt for sealed containers to prevent the onion from absorbing extra moisture or from drying out.  
  • Cooked – Well-wrapped cooked onions can last for up to five days in the fridge. Frozen cooked onions can last for up to three months.
halved onion

What Causes an Onion to Go Bad?

Your onions may go bad because of:  

  • Lack of Drying and Curing – Lack of drying and curing the onions after harvest can make them rot. Such onions begin to rot after 4-5 weeks in storage. They’ll have black/grey mold that starts from top-down.  
  • Poor Storage – If you’ve placed your onions in a well-lit and exposed area, they may easily go bad.  Too much sunlight exposure causes humidity and temperature changes, factors that cause your onions to rot. It’s best to store your onions in a dark, cool, and ventilated space like a pantry or cellar.  
  • Mixing Fresh and Old Onions – Buying a fresh batch of onions and storing it with other older onions may spoil the whole batch. The new onions can contract bacteria from rotting onions, which is why you need to check before storing your onions. Go through the old batch to determine if some onions need to be discarded before storing them.

5 Ways to Tell If an Onion Is Bad

All onions, whether red or white, have a shelf life and will eventually go bad.  Some of the ways you can spot a bad or spoiled onion include:

1. Discolored Skin

Onions that are about to go bad have dark or soft spots on the outside. Sometimes you may notice white, grey, or green mold on the onion.  

Mold-infested onions may also be gray and soft on the inside.

a lot of peel of rotten red onion

2. Squishy Flesh

You can also tell how fresh the onions are by touching and feeling them. An onion that’s about to go bad will have squishy flesh and won’t be firm.  

Fresh onions have firm flesh when squeezed and are not dried out. The outer skin should be dry and crisp.

3. Distinct Rotten Odor

A spoiled onion has a pungent odor similar to rotting compost.  Onions have a different scent when they are about to spoil and should be thrown away.  

4. Sprouting

onion seedling

An onion that’s sprouting from the top is about to go bad.  

However, you should not toss out sprouting onions that don’t have other problems like discolored skin, mold, or dry flesh. You’ll only need to remove the sprouts and use them if they are still firm.

5. Mold

Onions with mold have thin white hairs on the edge when cut. These onions may also feel slimy as you touch them. That’s an indication that the onion is about to go bad and needs to be discarded.

Can You Tell If an Onion Is Bad After Cooking?

Yes, it’s still possible to tell if an onion is bad after cooking.  

You may notice an unusual smell after cooking. Sliced onions may appear thin or slimy and can have a weird taste.

Tips For Buying Good Onions

When buying onions, it’s best to get onions that feel heavy, are firm, and don’t have any spots on them. They should also be dry and papery, wrapped in their skin. 

Choose whole peeled onions that have an outside layer that is still fresh. Avoid onions with bruises, spots, or cuts.

Red onions

Final Thoughts

Although onions tend to have a long shelf life, they can also quickly spoil if stored incorrectly. Onions with discolored skin, dark spots, or signs of mold should be discarded.  

It’s best to store your onions in a cool and dry space where there’s enough airflow. You can also refrigerate leftover onions in a sealed container for up to seven days.          


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