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Do Onions Go Bad? – What To Know

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Anything that comes in a 10lb bag should last forever, right?

Onions can be purchased in surprisingly large, bulk quantities and have an almost mythological reputation for being able to survive for months on end in cool, dark cellars.

But is any of that true?

Do onions go bad? Yes, onions do go bad. If stored properly, they can stay fresh and edible for up to 3 months, but they will mold under certain circumstances. Even if they don’t mold, onions will eventually shrivel and dry until they are not enjoyable.

In this article, we’ll talk about all the ways onions can and will go bad, how to prevent that from happening for as long as possible, and how to tell if your onions have passed their best before date.

We even get into a few deeper questions about onions, so read on to learn everything you need to know about preserving onions for long-term usage.

Can Onions Go Bad?

Onions, like essentially all other edible items, can and will go bad over time. They are very hearty and, if you store them correctly, you can keep them fresh and delicious for months at a time, but there is no guarantee of perfection.

There are a few different ways onions can go bad, depending on whether you’re dealing with whole onions, cut onions, or even green onions or scallions.

First, let’s discuss the difference between an onion that has started to grow, and is no longer ideal for consumption and an onion that has gone bad and is not necessarily safe for consumption. 

Do Whole Onions Go Bad?

Onions will start to sprout green stems after they’ve been stored for a long time.

You can eat an onion that has started to sprout; it is completely safe. However, an onion that has sprouted is likely getting rather old and you may have to remove a few outer layers that have gone dry or rubbery.

The sprout itself is also edible, but young sprouts tend to be quite bitter and you may not enjoy it. Unfortunately, the biggest problem with onions that have started to sprout is the amount of the onion that will be wasted.

Sometimes whole onions simply dry out and get shriveled up because they’ve been stored for too long.

As with sprouted onions, you can try peeling back a few of the outer layers to find fresh, crispy layers inside, but the older the onion is, the more you’ll have to remove.

And, of course, onions can go bad in the sense of growing mold and turning into a slimy, mushy, smelly mess. This is the worst-case scenario and generally happens when moisture gets into the area where your onions are stored.

Do Onions Absorb Bacteria?

There is a commonly accepted myth that sliced onions absorb bacteria. For some, this is thought to be a remedy to keep a body from getting sick. For others, it’s a nerve-wracking food safety concern.

If you place sliced onions inside your wool socks while you sleep, will it pull the toxins and bacteria out of your body?

If you slice onions and leave them on your counter, will they become a magnet for anything and everything that might be in the air?

There is no reliable evidence to show that sliced onions absorb, collect or attract bacteria or any other pathogens.

Yes, if you leave onions exposed they can become a breeding ground for foodborne bacteria, but no more than any other perishable food item. Regular food and health safety practices can and should be used around sliced onions.

Do Onions Go Bad If Not Refrigerated?

Yes, sliced or cut onions will go bad if they are not refrigerated.

As soon as the protective outer layer of the onion has been broken – aka, cut into – you should store it in an airtight container or sealable bag in your fridge, similar to all other food items in your kitchen. 

Whole onions, however, do not go bad quickly if they’re not refrigerated. In fact, it is better not to store your whole onions in the fridge if you want them to last longer with good quality. 

When onions are placed in a cold environment, the natural starch begins to convert to sugar.

A sweet onion may not sound like a terrible thing, but the transition also causes your onion to become soft and soggy without the support of the starch. The same thing happens to potatoes when refrigerated or kept in a very cold space.

This only applies to large, full-sized onions. Green onions, scallions, and scallions are entirely different kinds of onions. Their higher water content does require cold storage. 

How Do I Know If An Onion Is Bad?

The first sign that your onion is bad or going bad is discoloration or dark spots in the outer layers and skin. Dark brown or black areas of an onion indicate it has gone rotten or dried out beyond being appetizing.

Onions should always be firm, with no soft spots, sponginess, or bruises. It is normal for the outer layers to be dry and papery and, as an onion ages, the dryness will slowly work it’s way inwards.

You may have to peel a few layers to get to the freshest part of the onion, but this is normal. Peeling multiple soft layers is a bad sign, however, and you should probably discard the onion.

If you come across a little soft or brown spot inside your onion, you can simply cut out that area and eat the rest of the onion. 

Onion Mold

Black mold on the outer surface of your onion is not unusual. It comes from a fungus common in soil.

If you notice it, remove any onions that are affected and transfer them to a fridge until you can use them. The cold air will help keep the mold from spreading, but you will want to peel, rinse, and use the rest of your onion as quickly as you can.

If there are dark or black spots inside multiple layers of the onion, and it isn’t contained to just the papery outer layers, you may want to discard the entire onion.

White Liquid From Onion

If you’ve ever sliced an onion, you’ve probably seen the milky white liquid that seeps out.

This is not dangerous nor is it a sign of spoilage. It is the release of liquid stored inside the onion that combines with the natural sugars and starches. It’s entirely safe and natural.

Some onions release a more watery liquid whereas, in others, the liquid is white and opaque. Either way, your onion is safe to eat unless there are other, more concerning signs of spoilage.

What Happens if You Eat a Bad Onion?

Can bad onions make you sick? Possibly. Any edible item that has gone bad can make you sick. Although, onions aren’t overly or extremely dangerous, even if have gone bad.

Despite some myths, bad onions aren’t any more likely to cause food poisoning than any other food. 

If you find your onion has gone bad, you can remove the affected area and safely eat the rest.

If you happen to consume a piece that had begun to rot, it will probably taste bad and it may turn your stomach, but it’s not likely to cause any severe or lasting damage.

How to Store Onions

The secret to storing whole onions, still in their natural, papery wrapping is controlling temperature, humidity, and air circulation.

If you master these three elements, you’ll be able to keep your onions at their peak condition for the longest possible duration.

How to Keep an Onion Fresh

If you’d like to know how to preserve onions for months, follow these simple rules:

Temperature: Onions will last the longest if they are kept in a cool, but not cold, environment.

Your pantry or a cupboard should be perfect, as long as it is not directly beside your oven, under your sink, or in a basement or cellar that will become damp or extremely cold in winter conditions.

Ideally, you want your onions to be kept at a room temperature that is considered comfortable for sleeping in: between 60–70F.

Humidity: As with most foods, moisture is the enemy. If you want to keep your onions safe from mold, keep them dry. Bacteria can only grow and thrive with access to oxygen and water.

For this reason, cellars and basements are not actually ideal storage facilities for onions as they tend to be damp with high humidity levels. Instead, as already suggested, opt for a pantry.

Air circulation: Most bulk packages of onions are mesh, netted bags, not solid plastic. This is to allow air to easily flow around each onion, preventing any condensation to collect on your onions.

If you’ve bought or harvested onions individually, place them in a bowl without a lid, or a brown paper bag with some holes poked through them.

Try not to layer your onions on top of each other too much, because that will also prevent air from flowing freely between them, leading to bruising and potential mold issues. 

Aside from maintaining the right temperature, humidity, and air circulation, you also want to keep your onions away from any fruits or vegetables known to emit ethylene, the chemical responsible for ripening other surrounding foods.

The presence of ethylene increases the speed of spoiling. The primary culprits are bananas, tomatoes, apples, and melons.

How to Store A Cut Onion

Cut onions should always be stored in the fridge. For freshness, keep them in an airtight bag or container and try not to open and close the seal any more than necessary.

You want to prevent moisture from collecting inside the storage container or bag, and, the less you open it, the less it will contaminate the air and space around the onion with their potent gas.

If you want to protect the rest of the items in your fridge from tasting and smelling like onion, investing in the best onion keeper possible is a great idea. 

How Long Do Onions Last?

If you follow all the above recommendations proper storages, the shelf-life of an onion can be extended for up to 2–3 months.

If you don’t use them often, check them occasionally for soft spots or visible signs of spoilage, particularly after a few weeks have passed.

Much like apples, one bad onion can ruin the bunch. If you find any that are going bad, remove them from the rest as soon as possible to keep them from contaminating the others around them. 

How Long Can You Keep Onions?

How long an onion will last is a slightly different question from how long can you keep onions.

The answer to this is simple: you can keep onions as long as they have not gone bad. When an onion goes bad, it’s obvious and you should immediately dispose of it. Until then, keep storing them as safely as you can.

How Long Do Cut Onions Last?

Cut onions will stay fresh in your fridge, if properly stored in an airtight container, for up to 1 week or so.

Best practices suggest you should use them as soon as possible because the quality and nutritional value will deteriorate quickly, but as long as they’re not slimy to touch or have a bad smell, they should be fine.

To extend their life, limit the number of times you take them out of the fridge and/or open their container. With every new exposure to air, there is a higher risk of bacteria finding its way onto your onions.

It’s also a good idea to leave as much of the skin intact as possible, as this helps to keep the remaining onion fresh.

How Long do Green Onions Last in the Fridge?

Green onions are in the onion family, but they do not last as long as their larger, bulbous cousins. They’re much more delicate and fragile without the thick, papery protection.

Because of this difference, they shouldn’t be stored the same as standard onions; they won’t last in your pantry.

Fresh, green onions should be kept in the fridge, where they’ll last for 1–2 weeks.

To keep them from wilting or drying out, place them in a plastic bag that is sealed but has some air inside. Ideally, they’ll then go in the vegetable crisper where they won’t be crushed or buried under other items. 

As with regular onions, moisture is the enemy of green onions, scallions, and all other alliums in the family. If there is any moisture on your green onions, dry them before you store them.

You may also want to place a paper towel around your onion bunch and include it in the Ziploc bag. This will help keep your onions dry, even if some condensation occurs.

As with your other onions, living in the pantry, you want to check green onions that are being stored in your fridge occasionally.

As soon as one starts to soften or shows any sign of having mushy, spoiled pieces, remove it immediately to protect the rest of the bunch.

How Long Do Cooked Onions Last?

Cooked onions can be stored in an airtight container in your fridge for 2–3 days.

In a sauce or other dish, you can safely eat your leftovers up to 4 days after being carefully stored, but onions on their own will tend to go slimy after only a few days.

How Long Do Onions Last [CHART]

In a PantryIn Your Fridge
Fresh, whole onions2–3 months1–2 months
Chopped OnionsNot advisedUp to 1 week
Fresh Scallions/Green Onions1–5 days1–2 weeks
Cooked onionsNot advised2–3 days

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