Onions are a staple in many kitchens, used to add flavor and aroma to a variety of dishes. But like any fresh produce, onions can spoil. Knowing how to tell if an onion has gone bad can help you avoid ruining recipes or accidentally eating spoiled onions.
Signs an Onion Has Gone Bad
There are a few clear signs that indicate an onion has spoiled and should be discarded:
- Soft or mushy texture – Fresh onions should feel firm. If the onion feels soft, mushy or slimy, it has likely started to rot.
- Mold growth – Grayish fuzzy mold growing on the surface of the onion signals spoilage.
- Dark or sunken skin – The papery outer skin should be dry and crackly. Wrinkled, dark or sunken skin that feels moist or slimy indicates rot.
- Strong, foul odor – A putrid, rotting smell means the onion has gone bad.
- Discoloration – Black or dark, discolored patches on the onion flesh. Fresh onion flesh should be mostly white or pale yellow.
- Sprouting – Green sprouts coming out of the top of the onion is a sign it’s past its prime.
Even if there are no visible signs of spoilage, onions that have been stored for several months may lose their flavor and quality. Older onions are more likely to spoil faster.
Causes of Onion Spoilage
Onions spoil due to a variety of factors:
- Bacteria and fungi – Naturally present microbes can cause onions to rot, especially in warm, humid environments.
- Moisture – Excess moisture accelerates bacterial and fungal growth. Storing onions in insufficiently dry areas promotes spoilage.
- Physical damage – Cuts, bruises or other damage to the onion make it vulnerable to spoiling microorganisms.
- Temperature – Heat hastens onion spoilage. Storing onions at room temperature instead of cool, dry place cuts down their lifespan.
- Age – Like any produce, onions lose freshness and deteriorate in quality over time. Older onions spoil faster.
Onion Storage Tips
Proper storage is key to keeping onions fresh for as long as possible. Follow these tips:
- Store whole, unpeeled onions in a cool, dry, well-ventilated area like a pantry or basement. Avoid warm areas like near the stove.
- Place onions in a basket, mesh bag or open bowl with air circulation all around.
- Keep away from light to prevent sprouting.
- Don’t wash onions before storage – the extra moisture can speed up spoilage.
- If storing cut onions, seal tightly in an airtight container and refrigerate.
- Ideally use onions within a few weeks. Unspoiled whole onions can last 2-3 months with proper storage.
- Check frequently for any sprouting or signs of mold or slime.
- Store away from potatoes. The gases released as potatoes age can hasten onion spoilage.
What to Do With Onions That Have Gone Bad
If you discover an onion has spoiled, discard it right away. Some people advocate cutting away the spoiled portions and using the rest, but this is generally not recommended.
Bacteria that cause foodborne illness, like salmonella and E. coli, can spread throughout the onion as it spoils. It’s safest to throw out the entire onion to avoid any harmful bacteria.
While you can compost softer rotten onions, toss any onions with mold in the trash rather than the compost pile. Mold spores can survive and spread in compost.
How to Check an Onion for Freshness
When shopping, choose firm onions with dry, crackly outer skins. Avoid any with dark, damp or damaged skin. Check for the following signs your onion is fresh:
- Dry, papery outer skin
- Firm, compact with no soft spots
- Solid, not hollow feeling when gently squeezed
- No sprouting or green shoots
- Mild, onion-y aroma. No putrid or sour smell.
For cut onions, look for a bright white or pale yellow color without any dark or grayish discoloration.
How Long Do Onions Last?
With proper storage, whole onions have the following approximate shelf life:
| Onion Type | Refrigerator (35-40°F) | Pantry/Cellar (45-60°F) |
|---|---|---|
| Yellow, White, Red | 2-4 weeks | 2-3 months |
| Green (scallions) | 1-2 weeks | Not recommended |
Once cut, onions last approximately:
- Raw: 7 days in the fridge
- Cooked: 3-5 days in the fridge
Freezing extends shelf life to about 2-6 months for raw chopped onions, and 4-6 months for cooked onions.
Onion Safety and Foodborne Illness
Eating spoiled, moldy onions can cause foodborne illness. Onions may harbor bacteria like salmonella, E. coli, Bacillus cereus, and listeria, which can cause symptoms like:
- Nausea and vomiting
- Abdominal pain and diarrhea
- Fever and chills
- Headache
Food poisoning from produce like onions is often caused by cross-contamination with bacteria from raw meat, eggs or contaminated surfaces. Always practice good food safety habits like:
- Washing hands before and after handling food
- Using separate cutting boards and knives for produce and raw meats
- Cleaning kitchen surfaces after working with raw meat or eggs
- Refrigerating cut onions promptly
What Does a Bad Onion Smell Like?
A bad onion emits a putrid, rancid odor. The stench is often described as rotten, sour, or fermented. If you notice a particularly pungent, foul or ammonia-like smell, the onion has likely gone bad and should be discarded.
Can You Eat an Onion That Has Sprouted?
It’s best to avoid eating sprouted onions. The sprouts contain higher amounts of solanine, a toxic compound found in some nightshade vegetables. Solanine can cause symptoms like headache, nausea, and vomiting when consumed in excess.
However, removing sprouts from an otherwise firm, fresh-looking onion makes it safe to eat. Cut off any green shoots down to the white fleshy part before eating or cooking.
Conclusion
Checking onions for signs of spoilage like mold, mushy texture and foul odors can prevent foodborne illness. Discard any onions that have gone bad. Storing onions properly in a cool, dry place will extend their shelf life. Practice food safety and handle onions carefully to avoid cross-contamination from spoiled produce or raw meats. With proper storage and handling, onions can stay fresh for 2-3 months.