How Do You Know if an Onion Has Gone Bad?

Just like salt and pepper, onions are a staple when it comes to cooking. Without them, your dish would be incomplete. Onions are essential for flavor while holding numerous health and nutritional benefits.

Usually, onions are available loosely or pre-packed into bulk quantities. I typically try to buy just what I need. But what happens if the recipe calls for only half an onion? What if you have purchased one too many onions? How do you store them and keep them from fresh? How do you know if an onion has gone bad?

Here’s where I come in. I’ve researched everything there is to know about onions, so you do not need to. For example, the tell-tale signs of onions going bad and the different environments you can store onions, and how long they will last. Keep reading to learn how to know if an onion has gone bad, as well as tips to prolong the freshness of your onions.

How Do You Know if an Onion Has Gone Bad?

Onions, like all other fresh produce, are perishable. Onions are usually delivered fresh to the supermarket and have no definite best before date. So, you’ll have to keep track of the onions by the date of purchase.

Generally, you can expect your onions to last and remain fresh for a few months. However, it truly depends on the condition they are in and how you store them.

You’ll be able to tell if an onion has gone bad by the three basic tell-tale signs: color, touch, and smells. The tell-tale signs of a spoiled onion also depend on whether they are whole, chopped, or sliced. 

How Do You Know if a Whole Onion Has Gone Bad?

If your whole onion is soft and mushy, that is a definite sign that it is spoilt. A fresh onion should be firm and smooth. Black or brown spots on an onion are another sign of it going bad. These spots will eventually form mold on the surface of the onion. 

With that being said, you don’t necessarily have to throw them away. Salvage the good parts of the onion by carefully cutting off the mushy and black spots.

How Do You Know if a Chopped Onion Has Gone Bad?

Chopped and sliced onions should be refrigerated to maintain their freshness. However, that doesn’t mean they will last forever edible in the fridge. If the chopped onions are slimy and smell like anything other than an onion, they should be tossed in the bin.

What Does White Liquid from Onion Mean?

Firstly, white or clear liquid in any onion is perfectly normal. It doesn’t mean the onion has gone bad and you do not need to bin it. 

So why is there liquid oozing out when you are cutting an onion? Well, onions are porous and can hold water and nutrients rather well. Once you cut into an onion, it will release the onion cells’ water and nutritional content. In short, you can call it raw onion juice. Usually, fresh onions are juicy and contain a lot of water content. Older onions will dry out and turn leathery. 

Also, wondering why onions irritate your eyes and make you cry? It’s induced by a gas chemical found in the raw onion juice called propanethial S-oxide. This gas irritates your eyes and causes you to tear.

Black Mold on Surface of Onion

Black mold on onions is a common problem. It’s caused by a fungus found in soil called aspergillus niger. It usually starts at the top of the bulb and makes its way to the bottom. 

Why is there Black Mold?

Mold is a pesky and unavoidable matter. Here are a few reasons why your onion maybe moldy:

  • Bruised onions from dropping them or bumping into other onions – the bruised areas are a pathway for fungus to enter and cause it to be moldy
  • Unsanitary conditions or bacteria from nearby moldy vegetables
  • Poor air circulation and high humidity allow the fungus to prosper and grow

Does Black Mold Mean the Onion Has Gone Bad?

You will be glad to know that you do not need to immediately toss away a moldy onion. As long as the onion has not been severely affected by mold or is soft and mushy, it is good to eat. 

You can peel off the moldy layer of the onion or cut off the moldy parts. Wash the onion and consume it as soon as possible. 

Inhaling or ingesting aspergillus niger rarely causes food allergies. However, you are advised not to eat the onion if you are allergic to aspergillus.

What Happens if You Eat Bad Onions?

Breathe. Eating a gone off onion will not kill you. Onions and shallots are some of the safest vegetables. Most people walk away with no symptoms or with a slightly upset stomach. In most cases the worst thing to happen when an onion has gone bad is that the taste is unpleasant. Granted, ruining the flavor of your dish isn’t a small issue!

In most instances, food reactions are not because of a lousy onion but because of other factors. Factors such as having an allergy or not washing your onions properly, or cross-contamination in the kitchen. So, it’s important to remember to keep your kitchen surfaces clean.

How Long Do Onions Last in the Fridge?

Storing onions in the fridge is usually not advised, as you have learned onions should be stored in a dry and well-ventilated place. If not, onions will get mushy and rot.

However, storing onions in the fridge could extend their shelf life, mainly if they have been chopped or cooked. 

Whole raw onions can be kept in the fridge for two to three months. Peeled raw onions can last up to 10-14 days refrigerated. Fresh chopped or sliced onions can be refrigerated for as long as 10 days when stored properly. You should wrap the onions in plastic or store them in a clean airtight container. This will prevent cross-contamination as well as stop you from stinking up your fridge with onion.

Raw onions would still be safe to eat after this period. However, the texture may become slightly soft and mushy due to the moisture. You may also notice that they lose some of their characteristic taste.

On the other hand, cooked onions should be eaten as soon as possible. They can only last up to three to five days refrigerated. Store them in the fridge inside an airtight container.

How Long Do Onions Last in the Freezer?

Freezing raw onions will give them a maximum shelf life of up to eight months. Chopped or sliced onions can be frozen for three to six months. You can also freeze cooked onions and store them in the freezer for up to 12 months.

How Long Do Onions Last in the Cupboard?

If you are like me and store your onions in the kitchen cupboard, you can expect your onions to last for two to three months. With that being said, the onions should be appropriately stored in a cool, around 45–55-degree F, dark and well-ventilated area.

The onions could last longer than this period. It would be best to periodically check on them every now and then to ensure no mold is growing.

How Long Do Onions Last at Room Temperature?

If you cannot find a well-ventilated or cool area to store your whole raw onions, they can last up to a week at room temperature. Of course, this varies to every situation and whether they have been stored properly. After a week, regularly check for any mold and if your onions have gone bad.

How to Properly Store Onions

Storing Whole Raw Onions

  • Find a cool, dark, and well-ventilated area to store your onions. Such as the basement, in your kitchen cabinet, or your pantry
  • Remove onions from the plastic bag, if any – plastic bags will cause your onions to go bad quickly due to poor ventilation
  • Keep onions in a mesh bag, paper bag with punched holes, or a container without the lid on – to ensure ample air circulation
  • Try not to store onions next to potatoes – Onions release ethylene gas, which will cause the potatoes to sprout. The moisture from both vegetables will also cause them to spoil faster.

Storing Chopped and Cooked Onions

Once peeled, chopped or diced, or cooked, store them in a clean airtight container or plastic bag in the refrigerator. Cooked onions should be consumed as soon as possible.

How to Freeze Onions

Freezing onions is easy and a great way to extend their shelf life. 

Freezing whole onions is generally not advised as this would lead to a mushy mess when thawed. However, freezing them in chunks is perfect. Here is how you can freeze onions:

  1. Peel and chop or dice your onions in whatever shape you like.
  2. Spread the chopped onions on a tray and freeze for a few hours. (This step is crucial to not resulting in a clump of onion cubes stuck together)
  3. Quickly remove the tray from the freezer and divide the onions into clean bags or airtight containers.
  4. Label the bags and store them in the freezer. They will be good to freeze for up to 12 months if stored properly.

Be warned, frozen onions will be mushy and not as crisp as fresh onions, but the taste of frozen onions are as good as fresh onions. Frozen onions are best for soups, stews, and almost every dish. No thawing is needed, just toss them in, and you can get cooking.