Onions are wonderful to cook with and keep for a surprisingly long time when stored correctly, but it's important to know how to tell if an onion has gone bad and should be discarded.
Old, rotten onions don't taste good and will ruin the flavor of your food. When using onions the first thing you should do is make sure they are fresh and free from any of the issues listed below.
Fresh onions will be firm and smell slightly sweet. They should be free of blemishes, mold, and any "furry" looking textures. A good onion can be stored for a long time but will go bad quickly if kept in moist conditions.
Signs of Rot in Onions
Look for these signs to see if an onion has gone bad.
- Mold - older onions may develop white, green, or black mold. Sometimes it grows on the papery skin exterior of the onion or it may be closer to the center of the onion.
- Soft Spots - the easiest way to spot a bad onion is if it has mushy spots, brown spots, black spots, or a slimy texture. These may look like indentations or they may just be discolorations.
- Sprouting - sprouting may be visible before or after cutting into the onion. Onions that are sprouting will look like they have fingers growing up through them and may have green sprouts growing out of them.
- Smell - if the onion has a strong smell that's acrid or ammonia-like, it may be past its prime.
The Best Way to Store Onions
Whole onions are best when kept in a cool (or room temperature), dark place (like a pantry or cellar) that's dry. You can place them in a basket or other type of container, without a lid, that gets ventilation.
If you buy them in a large bag from the grocery store, the bag can be hung in a pantry or cellar.
With proper storage, you can keep whole, raw onions for up to 3 months.
If you want to store chopped onion or cooked onion, it will keep for up to 1 week in the refrigerator in an airtight container or resealable bag or up to 6 months in the freezer in a freezer bag or other freezer-safe container.
If you'd like to keep half a cut onion, wrap it in plastic wrap and keep it in the refrigerator for up to 1 week.
Onion FAQs
Can you eat a sprouted onion?
The short answer is yes, but you may not want to. If a sprouted onion has no visible mold or dark spots, you can technically eat it but it probably won't taste as good.
In some cases, the outer layers and center sprouts can be removed and you can eat the onion. I would only do this if I was using the onion in a cooked dish like soup and not fresh in a salad.
Sprouted onions are more fibrous and less sweet than newer onions. The sprout sucks the water out of the onion in order to grow, so they tend to be more bitter.
What does a bad onion taste like?
Bad or old onions will have a pungent, somewhat acrid smell. Ripe onions should smell slightly sweet, but rotten onions will have a strong ammonia smell that is very noticeable.
Bad onions will make your eyes water profusely when you cut them, as they have an almost overpowering smell.
How long does it take for an onion to go bad?
Onions can keep from 1 to 3 months in your pantry, depending on how they are stored.
Like all fresh vegetables, the shelf life of onions depends on the conditions they are kept in. You want to keep onions in a cool (not cold), dark, and dry place.
When are onions in season?
Onions are available in most grocery stores year-round. They are typically planted in mid-Spring and harvested throughout the summer and fall.
Onions harvested in the fall are sold throughout the winter and have a thicker skin and slightly less sweet flavor.
What types of onions are there?
There are many types of onions - the most common of which include yellow onions (also called brown onions), sweet onions, white onions, red onions, shallots, green onions, or spring onions.
What do rotten onions taste like?
A rotten onion will be bitter, fibrous, and lacking in moisture and sweetness.
Can you freeze onions?
Yes, you can freeze onions. The easiest way to do it is to dice them and store them in a freezer-safe plastic bag or airtight container for up to 6 months.
How long do cut onions last?
Cut onions can be kept for up to 1 week in the refrigerator in an airtight container.
Sometimes you only need half an onion and want to save the rest of the onion for later in the week. If you open up the container and it has a bad onion smell, I would recommend throwing it out.