Onions are a common ingredient used in many dishes. They add great flavor and aroma to foods. However, like any fresh produce, onions can spoil over time. So what do you do if you discover an onion that has gone bad? Can you still use it in cooking, or is it unsafe to eat? Here’s a look at how to tell if an onion has gone bad and whether it’s okay to eat onions past their prime.
How can you tell if an onion has gone bad?
There are a few clear signs that indicate an onion has spoiled and is no longer good to eat:
- Mold – If you notice any fuzzy blue, green or white mold growing on the onion, it has definitely gone bad. Mold spores can spread through the onion and make it unsafe to eat.
- Slimy texture – A very soft, mushy or slimy feel indicates the onion is rotting and decomposing. This texture change happens when bacteria begin breaking down the onion’s tissues.
- Shriveled and dried appearance – Over time, onions lose moisture. As they dry out, the onion skins get crinkly, papery and dried out. Older onions may also get soft spots or bald patches where the outer skin slips off.
- Brown, discolored flesh – When you cut into a bad onion, you may notice brown, yellow or grayish streaks in the flesh. This discoloration happens as mold and bacteria spread through the inside layers.
- Strong, unpleasant odor – Fresh onions should have a pungent, spicy aroma. Rotten onions give off an ammonia-like, foul, or fermented smell.
Generally, if an onion shows any of these signs, it has gone bad and reached the end of its shelf life. Toss damaged, moldy or foul-smelling onions in the garbage or compost pile.
What causes onions to spoil?
Onions can go bad for a few different reasons:
- Moisture – Raw onions have a high water content. Moisture supports microbial growth and speeds up decomposition. Cut onions and pieces left in air start drying out, making spoilage more likely.
- Bruised or damaged outer skins – Injuries to the thin, papery skins allow microbes to enter and multiply inside the bulb. Intact skins protect the onion’s flesh and help retain moisture.
- Temperature – Warm conditions promote faster bacteria and mold growth. Storing onions at cool room temperatures helps maximize freshness.
- Age – Like any produce, onions have a limited shelf life. Over several weeks, they lose firmness and moisture and eventually shrivel and rot.
Proper onion storage – whole, dry, uncut, in a cool pantry or fridge – minimizes risks of spoilage and extends shelf life.
Can you eat onions that have sprouted?
Finding little green sprouts growing out of an onion bulb is common. These sprouts may look strange, but they don’t necessarily mean the onion has gone bad.
Onions form these sprouts when the bulbs sit for weeks or months. It’s the onion plant’s natural way of trying to keep growing. The sprouts themselves are perfectly fine to eat. However, onions with sprouts do have a shorter shelf life.
If the sprouted onion still smells fresh and feels firm, with no mushy textures or spots, it should be safe to use. Simply pull or cut off the sprouts and roots and use the remainder of the onion bulb as normal. Make sure sprouted onions are cooked thoroughly before eating.
Can you eat moldy onions?
If an onion has mold growing on the surface, it’s best to throw it out. Onion mold often starts as a fuzzy white patch that eventually turns green or blue-gray as spores develop. Moldy onions may also get soft brown spots.
Mold spreads quickly through the moist inside layers of an onion. The fungi’s root threads intertwine with the onion’s tissues, so you can’t simply scrub or peel off moldy parts. Eating onions contaminated with mold can cause allergic reactions or respiratory irritation. It’s also possible for some molds to produce toxins that cause food poisoning symptoms.
To avoid cross-contamination, discard moldy onions in a sealed bag. Clean any containers and refrigerator drawers where you stored them.
What about onions with dark spots?
Dark brown or black splotches on an onion’s skin are usually just superficial staining. Whole, intact onions frequently develop these harmless dark patches after longer storage periods. The discoloration is simply cosmetic and does not mean the onion is dangerous to eat.
However, if you slice into an onion and see extensive dark brown or gray streaks permeating the flesh, it’s gone bad. Those discolorations indicate bacterial decay in the inner layers that can make the onion toxic. Toss onions with dark interior discoloration in the garbage immediately.
Can you freeze onions that are about to go bad?
Freezing is a smart way to rescue onions that are on the verge of going bad. As long as the onion still looks and smells fresh, with no visible mold, freezing can pause the spoiling process.
To freeze whole onions:
- Peel and chop the onions first. Cut into halves, slices, diced pieces or purée in a blender.
- Transfer the prepped onion to an airtight freezer container or zip-top plastic freezer bag.
- Remove excess air from bags before sealing. This prevents freezer burn.
- Label the container with the date.
- Freeze for up to 3 months.
Never freeze onions that show signs of mold or soft rotting textures. Freezing can’t improve the quality or reverse actual spoilage.
What does an onion look and smell like when it has gone bad?
Here are the most common visual and odor indications that an onion has spoiled and should be discarded:
- Appearance – Moldy growth, brown or black skin discolorations, soft or mushy textures, visible denting, or shriveled dryness.
- Odor – Strong, foul, sour, fermented or ammonia-like smell instead of pungent fresh onion aroma.
An onion may still look alright visually but give off an “off” odor, which means it should not be eaten. Trust your senses – if an onion has gone bad in any way, you’ll know it.
Can you cut out the bad part of an onion?
With fruits like apples and pears, you can often salvage the good sections by cutting away visibly rotten or moldy spots. But this is risky to attempt with onions, since decay and mold spread rapidly through the layers.
If there’s just a small isolated spoiled area on one part of the onion, you might try trimming out a 1-inch margin around the bad spot. Make sure no discoloration remains. However, it’s difficult to be certain you removed every bit of contamination, so the safest option is tossing the entire onion.
Is it okay to eat sprouted, shrivelled or aging onions?
Eating these types of onions may be fine in some cases, with caution:
- Sprouted onions – Safe to eat after removing sprouts; cook thoroughly.
- Shrivelled onions – Trim dry, papery outer skins; inspect flesh for mold or sliminess.
- Aging onions – Check for softness, dark moldy spots; refrigerate to slow further spoiling.
Always inspect the interior onion flesh closely and look for signs of contamination. If in doubt, throw it out.
Can you make onion powder from onions past their prime?
As long as the onions are intact and show no mold, yes you can dry older onions to make homemade onion powder:
- Peel and chop onions into quarters or smaller. Rinse off any loose skin.
- Arrange chopped onions on a baking sheet in a single layer.
- Bake at 200oF for 2 to 4 hours, stirring occasionally, until completely dried out.
- Remove from oven and let cool.
- Working in batches, grind dried onions into a fine powder using a blender or food processor.
- Store in an airtight container in a cool, dark place for 6 months to 1 year.
Onion powder is a great way to prevent waste and make older onions last longer. Just avoid making powder from any onions that are moldy or rotten.
What happens if you eat onions that have gone bad?
Eating spoiled, moldy onions can cause foodborne illness. Symptoms can include:
- Nausea, vomiting, diarrhea
- Abdominal pain, cramps
- Headache, fever, fatigue
- Respiratory irritation (from inhalation of onion mold spores)
Severe cases may lead to dehydration or long-lasting health issues. Some molds even generate mycotoxins that can cause chronic toxicity with repeated exposure.
If you experience symptoms after eating an onion that tasted off or looked rotten, see a doctor. Protect your health by only consuming onion bulbs that are fresh and healthy.
How can you avoid onions going bad?
Proper storage is key to extending onions’ shelf life and use-by date. Follow these tips:
- Keep onions whole, dry, and with intact skins until ready to use. Don’t peel or chop until ready to cook.
- Choose firm, unbruised bulbs without moldy or soft spots.
- Store unwashed onions in a cool, well-ventilated area, around 40-50°F if possible.
- Separate onions into breathable mesh or paper bags. Avoid piling them.
- Place onions away from light sources like windows or appliances.
- Check frequently and remove any onions showing decay.
With ideal storage conditions, whole raw onions can last 2-3 months or longer. Once cut, use within 7-10 days.
What are some substitutes if you don’t have fresh onions?
If you discover your onions have gone bad right when a recipe calls for them, here are some handy replacements:
- Onion powder or onion flakes
- Dried minced onion
- Frozen chopped onions
- Fresh shallots or leeks
- Garlic or garlic powder
- Asafoetida powder (has an onion-like taste)
- Scallions or green onions (for garnish)
In most cooked dishes, onion powder or dried minced onion can substitute for fresh onion at a 1:1 ratio. Adjust amounts to taste.
Can you cook with sprouted onions?
Yes, sprouted onions can still be used in recipes. Simply remove the sprout and roots and cook the onion bulb thoroughly.
In cooked dishes like soups, stews, caramelized onions, etc. the onion pieces soften during extended cooking times anyways. Just monitor sprouted onions closely for any off odors or mushy textures.
Avoid eating sprouted onions raw. And refrigerate sprouted onions and use within a few days for best quality and safety.
Conclusion
While onions last a long time compared to other produce, they will eventually spoil. Signs an onion has gone bad include mold growth, dark spotty flesh, foul odors, mushy texture, and excessive shriveling.
Eating spoiled, moldy onions poses a health risk and can cause foodborne illness. However, onions showing a few sprouts or just minor outer skin shriveling can still be used if they appear and smell fresh. Trim any iffy portions and cook the onion thoroughly.
Storing onions properly in a cool, dry place can maximize shelf life. But it’s still important to check onion bulbs periodically and discard any that show signs of rotting. With careful inspection and handling, most onions can be safely used for weeks or months past their purchase date.
