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Are Moldy Onions Safe to Eat?


Reading Time: 6 minutes

Onions are some of the most resilient against rot and decay as fresh vegetables go. Unlike other fresh vegetables and herbs, onions can last for months in storage without refrigeration or cold storage measures. But they, too, can go wrong and rot from the inside. So at what point is an onion no longer safe to eat?

If you find yourself with severely moldy onions, discard them immediately. A severely moldy onion can harbor some dangerous molds that can create health problems, even if finely chopped and cooked into another dish.

Even the mildly affected onions should be disposed of at the first sign of mold. Mold can spread from onion to onion, especially if they’re stored together in a basket or other container. If you’re going to cook with severely moldy onions, cut off the moldy areas and the root end of the onion first, making sure to discard those parts.

It’s important to note that onions are very absorbent vegetables. They will take on the flavors of anything near them, especially if they’re stored together with other items that have strong scents or flavors. So make sure your onions aren’t too close to overly fragrant foods in storage.

How Can You Tell if Onions Are Bad Once Cooked?

Onions that have gone bad through mold, rot, or bacterial growth take on a darker color and taste bad. Eating bad onions can bring about various complications, such as food poisoning. So, it’s always best to discard them.

Health Dangers Posed by Moldy Food

Not all kinds of mold are bad for food. Indeed, some genera of mold are used in the preparation of certain foods. But visibly moldy food, especially with black spots or mucous and smelly texture, can be dangerous for human and animal health.

Moldy foods often have certain kinds of fungal toxins called mycotoxins. Mycotoxins such as aflatoxin are responsible for the most serious cases of food poisoning, according to the World Health Organization (WHO).

Eating food with mold can potentially produce toxins that can lead to death, chiefly through liver poisoning. There is also evidence that some toxins found in food mold can cause liver cancer in humans.

How and Why Do Onions Go Bad?

The major reason why onions go bad is due to black mold growth. This most often happens after harvest but can also occur before, especially if the onion bulbs are past maturity or if they get wounded by tools or pest attacks.

The major cause of black mold on onions is a fungus known as Aspergillus niger. An A. niger attack manifests as moldy spots, patches, and streaks on the onion’s outer scales.

The fungus responsible for the black mold can enter the onion in a variety of ways. Mostly it is through tiny tears and wounds on the surface of the onion bulbs. However, in a post-harvest situation, the mold can also enter through the drying neck of the bulbs.

How Do You Identify Moldy or Rotten Onions?

While some onions with black mold are easy to identify, signs of mold or rot often don’t show up on the outer scales of the bulbs. You notice the damage only after peeling off the dry outer scales or cutting such onions.

Here is a guide on how to notice bad onions as a result of rot or other forms of damage:

Whole Onions

Some of the damage on whole onions is often a result of bad storage. When onions, especially those with a layer of dry skin or perhaps a thin paper covering, are stored in dark and damp places for long periods of time, they begin to sprout. The sprouts growing from the bulbs are called “neck sprouts” because they grow from the dried neck area of the onion.

Often, these neck sprouts turn black and moldy when exposed to damp, dark conditions. If you notice black spots on your whole onion bulbs, cut them open and check for these neck sprouts that may have turned into black and wet patches. If such is the case, discard the onions immediately because they are no longer safe to eat.

Peeled or Cut Onions

If you remove the dried outer layer of onion scales after peeling your onions, don’t be surprised to find blackish mold on the cut parts. This is another sign that the onions are bad and should not be eaten.

Onions That Start Looking or Smelling Bad

Bad smelling or rotten onions usually have a dark, wet texture with soft spots on them. If you have not cut into your peeled or halved onions yet, check for these signs of mold now before cooking with the onions.

Onion Black Mold Control in the Field

Black mold control in onions should start right from the field during cultivation. This is why it’s important to grow your onions in a suitable environment free from the main causes of the fungus attack. Here are some of the things that you should do to keep mold in onions at bay;

Keep Your Onions Weeded and the Garden Clean

Keeping your onion garden free of weeds and litter will help prevent the infestation of A. niger and other common fungus varieties. Indeed, regular and thorough weeding of your onions is the most important measure to discourage mold growth in the garden.

But it is not enough to pull off the weeds. The dead weeds constitute a mass of vegetative matter that will encourage mold infestation of the growing onions if it starts decaying. That is why you should collect the uprooted weeds and dispose of them far from the onion garden.

Apply Pest Control

Pests also contribute to onions growing moldy in the garden. A. niger is the same fungus that attacks onions in the garden and in storage. You can prevent its infestation by controlling pests, especially burrowing and attacking the growing onion bulbs beneath the soil.

Instead of using pesticides to control mold growth, you should consider natural pest control approaches. An effective one is rotating the onion crop with other crops. For the best results, rotate the onions with crops other than those in the onion family (Alliaceae).

Ensure Good Drainage

If the soil in which your onions grow is too soggy due to poor drainage, the likelihood of mold infestation increases. Ensure good drainage such that your onion crop remains adequately watered but not too much to encourage uncontrolled mold growth.

Harvest Your Onions Carefully

Harvest your onion bulbs carefully. A. niger fungi are more likely to infest onion bulbs which have cuts and bruises on the surface. It is best to use your hands and not tools in pulling the bulbs out of the ground.

Controlling Mold in Storage

A lot of the mold affecting onions grows when they are in storage. How you store onions can either increase or reduce the chances of mold growth. Onions that are dried to a certain extent before storage can withstand a lot of invasion from different types of fungi. Here’s are various ways you can employ to prevent your onions from going bad;

– Store onions in a cool and dry place without wetting them. Always ensure they’re properly sealed if you are to store them in a refrigerator.

– Do not allow the onions to come into contact with water or dampness very often or for long periods of time. This is bad because it makes onions rot even faster than they would if they were dry and well taken care of.

-Store onions away from potatoes, especially if you are storing them in a dark place. The potatoes will give off a bad smell that is bad for the onions.

-If you must store onions in a damp or dark place, do not store them together with other vegetables like tomatoes, that are even more prone to bad mold than onions. If in a refrigerator, ensure they are in an airtight container

Ensure not to keep your peeled and cut onions near open windows because they’re likely to become contaminated by bad germs and spores in the air.

-If you store peeled onions in an airtight container, don’t forget to place a garlic clove among them because this will prevent rot from setting in while adding flavor to the onions at the same time.

– If bad onion signs are already present on your peeled or halved onions, it is best to discard these onions entirely rather than risk their potential only to make you sick.

-If your peeled and cut onions don’t appear well taken care of or if they have already turned dark or bad-smelling, do not cook them for too long at once. That will only accelerate the rotting process even further because heat makes food rot faster.

If you notice a bad smell in your kitchen when cooking with onions, it is good to open windows and turn on the exhaust fans. That is because strong smells from cooking will only make bad onions rot faster.

-Don’t forget that hot oil can also promote rot in cut or peeled onions, so do not cut and peel them in the same room where you will be cooking.

How Do You Know if Moldy Onions Are Safe to Eat?

Even if your onion bulbs show visible mold spots, they may still be safe to eat on the outer layers. You can peel off the affected layers, and if the rest of the onion is fresh and natural in appearance, you can go ahead to include it in your food.

According to the best food science practices, taking off the moldy outer layer of a moldy onion is not enough. You should still thoroughly clean the unaffected portion thoroughly before it is consumed.

Soaking the onion in cold salt water for about an hour before washing it will remove any remaining bad mold spores. You should also slice off bad parts of the onion bulb before peeling it to make sure no moldy bits get into your cooking.

When in doubt, discard!










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