How to Tell If an Onion Is Bad (The 3 Signs)

Published Categorized as Food
How to Tell If an Onion Is Bad (The 3 Signs)Maria Karabella /Depositphotos

Stop trying to guess if the onions in your pantry are bad or not. This illustrated, no-B.S. guide will show you how to find out.

Much can be said about the humble onion—the pungent bulb of the onion plant and a close relative of garlic.

Onions don’t cost much, they can be picked up in any grocery store, and they can be used in a variety of ways, from being added to salads to sweated on the stove to roasted in the oven.

Another thing to like about onions is that they keep for weeks, especially if you store them properly. (By “properly,” I mean in a cool, dark, dry, and well-ventilated place, such as a wicker basket on a shelf in your pantry.)

Alas, as long as you can keep them, onions don’t last forever. And if they spoil, they should nary be eaten raw nor cooked with as they may no longer be edible. To help you determine if that’s the case with the alliums in your pantry, let’s talk about the tell-tale signs of onion spoilage.

How to Tell If an Onion Is Spoiled

An onion is spoiled if it looks wilted, is moldy at the ends, and/or leaks liquid. If the flesh is bruised and browned after the onion is cut open, this is another sign that the onion has gone bad and should be discarded.

The best way to get rid of spoiled onions is to throw them on the compost pile. Because onions tend to sprout when whole, you need to cut them up for composting—preferably, into quarters to hasten the decomposition.

1. Examine the Bulb

An illustration of a fresh yellow onion (left) compared to an old and spoiled yellow onion (right).

An onion at its best should be firm and plump—heavy for its weight, the skin filled, without sprouting or mold. If you hold it in your hand and squeeze it lightly, it should give resistance and hold its shape.

If the onion has sprouted, it’s old but may still be salvageable. However, if it’s withered, oozing brown liquid, or moldy at the stem and root ends, it’s spoiled and should be discarded.

2. Give It a Good Whiff

Take the onion in your hand and hold it to your nose. Then brace yourself and give it a vigorous sniff. Does anything smell off?

If the onion is still good, it should almost have no smell. (Some varieties will smell slightly sweet or pleasantly pungent.) If it smells musty and medicinal, or fermented and sour, it should raise eyebrows. This is a sign of mold formation and the activity of spoilage bacteria.

3. Cut It Open and Look at the Flesh

An illustration of a fresh yellow onion cut in half (left) compared to an old and spoiled yellow onion cut in half (right).

Peel the onion, cut both ends off, and then slice it in half. If the blade of the knife can be pushed in without resistance—or brownish liquid oozes out of the onion as you cut it—this is already a sign that the onion is spoiled.

White onions should be white, yellow onions should be yellow, and red onions should be red. If you notice excessive bruising, browning, and mushiness, discard the entire onion and don’t try to eat or cook any part of it.

Are Sprouted Onions Safe to Eat?

A sprouted onion is an onion that’s old, but not necessarily spoiled. To grow, the sprout uses up moisture and sugar from the bulb, so, as the good folks at Cook’s Illustrated established in a taste test, sprouted onions taste bitter and have a tough and stringy mouthfeel.

In their 2017 book titled Scraps, Wilt & Weeds, Danish chef Mads Refslund and American forager Tama Matsuoka Wong write that sprouted onions, unlike sprouted potatoes, are safe to eat.

Discard the green sprout and use up the rest of the onion. If you roast it slowly in the oven, at 350°F (180°C) for 1 hour, it will turn out soft, sweet, and irresistible.

Can Eating Spoiled Onions Make You Sick?

For the most part, the bacteria, fungi, molds, and yeasts that spoil our food don’t cause foodborne illness, writes Michelle Jarvie for the news section of the Michigan State University Extension’s website.

However, the pathogenic bacteria that grow alongside them, such as Listeria monocytogenes or Salmonella, and the heat-resistant toxins they leave in our food can cause potentially life-threatening food poisoning.

You should never eat spoiled onions because there’s no way for you to know whether they’re still edible or not. Unlike spoilage bacteria, which change the smell, taste, and mouthfeel of the onions, pathogenic bacteria are undetectable to humans.

If an onion is spoiled, it’s been sitting in your pantry or fridge long enough for you to assume that it may also be overgrown with disease-causing bacteria—and they may have found their way into the flesh of the onion from the infected surface.

Which Onions Last the Longest?

Botanists have identified as many as 920 varieties of onions out there, but only a handful of them are economical enough to be grown and sold on the scale of modern society.

Depending on the time of year, there are two types of onions in the grocery store: spring onions and storage onions, and their names already give subtle clues about their shelf life.

Spring onions, planted in fall and harvested in spring, are luscious and sweet thanks to the fact that they’re full of moisture and sugar. They last for 1-2 weeks and must be kept in the fridge.

Storage onions, planted in spring and harvested midsummer, are dry and pungent. They are best kept in the pantry, where, depending on the variety, they will keep their best quality for weeks.

The most common types of storage onions at the store are yellow onions, white onions, and red onions. As a rule of thumb, yellow onions are the cheapest, easiest to store, and have the longest shelf life. White onions and red onions, on the other hand, are more expensive and perishable.

How to Store Onions

Store spring onions in the crisper drawer of your fridge, where they will keep for 1-2 weeks depending on how fresh they were when you bought them.

Store onions and potatoes separately, especially in the refrigerator. Onions and potatoes release moisture, so they will spoil faster if they are stored together. Contrary to popular belief, neither produces ethylene gas, although both are sensitive to it because it accelerates their germination.

Storage onions shouldn’t be kept in the fridge. Stack them in a crate or a wicker basket, one on top of the other, but with some room to breathe, and then store them on the shelving of your pantry or in a closed cabinet. Yellow onions will keep for a few months; white and red onions for a few weeks.

Keep onions away from direct sunlight and sources of heat. Don’t store them on the windowsill or in well-lit areas of your kitchen, and avoid putting them close to the stove, fridge, freezer, or heating and hot water pipes in your home.

In Conclusion

If the onions in your kitchen are old, you have stored them in a warm place, or you simply suspect they may be spoiled, look for the tell-tale signs of onion spoilage: Wilted bulbs that ooze brown liquid, smell musty and medicinal, and have browned, mushy flesh.

Rule number one of food safety is, “When in doubt, throw it out.” Dispose of spoiled onions by cutting them up into quarters and throwing them on the compost pile, where they provide valuable nutrients for the soil.

By Jim Stonos

When Jim isn't in the kitchen, he is usually spending time with family and friends, and working with the HCW editorial team to answer the questions he used to ask himself back when he was learning the ropes of cooking.

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