Mold On Nuts: Aflatoxins And Their Dangers

Discovering mold on a bag or package of nuts you planned to snack on can cause you to lose your appetite quickly. Worse yet, moldy nuts may have aflatoxins as well. What are aflatoxins and are they and moldy nuts dangerous?

This guide to mold on nuts and the aflatoxins that can result will present a lot of useful information that can keep you and your family safe. Make sure you keep reading.

Aflatoxins are a specific type of fungi that thrives in humid and warm environments. One’s risk of liver cancer can increase from aflatoxin exposure. If you see moldy nuts, it’s best to soak them before you eat them, this will remove the mold and therefore the risk of ingesting aflatoxins.

Mold on nuts

Do Nuts Go Moldy?

Before nuts ever reach your favorite grocery store, they’re harvested, prepared, and then stashed in storage bins.

The storage period can last for weeks and sometimes even months, which can lead to the development of mold.

This mold has a name, mycotoxins.

Mycotoxins are a type of secondary metabolite that are fungal in nature. Aflatoxins are a kind of mycotoxin, but we’ll discuss aflatoxins more a little bit later.

Besides the mold that could be packaged in your container or jar of nuts, there is also mold that can develop without proper nut storage.

Avoid heat, oxygen, and light. The unsaturated fat content in nuts can increase their rate of rancidity in these conditions, which could also accelerate the development of mold.

What Does Mold on Nuts Look Like?

The trouble with distinguishing mold on nuts is that you can’t always see it.

The mold isn’t like the fuzzy blue stuff that grows on loaves of bread or ears of corn.

Of course, the mold can be fuzzy and colorful, but the mycotoxin mold is much harder to visually distinguish.

That’s a huge part of how you can end up eating nuts contaminated with mycotoxins and not even realize it.

What Kind of Mold Grows on Nuts?

The mold that grows on nuts is aspergillus.

Aspergillus grows natively in crop soil. As a fungus, it can spread to the crops themselves, especially tree nuts, grains, and legumes.

Once infected by the fungal strain, the crops become weakened, and dieback could occur.

For those crops that do survive, when they’re eventually harvested and stored, they can rot. That’s especially the case for nuts and grains.

At that point, the farmer has taken the time to grow, harvest, and process the crops but will not see any return on investment for their time due to the poor condition of the crops.

Aspergillus also produces mycotoxins.

How to Prevent Mold from Growing on Nuts

Proper storage conditions once you buy a package or container of nuts will safeguard them from mold while the nuts are in your possession, but what about the mycotoxins that might already be on there?

Before you eat nuts, there’s a simple solution for removing the mold. Soak the nuts!

Here’s how.

  1. Transfer the uneaten nuts to a mason jar or bowl. There’s no need to cover it with a lid.
  2. Fill a container with filtered water and pour half the water over the nuts.
  3. With the remaining water, stir in some table salt. For each quart of water in the container, you need a tablespoon of table salt. Use a wooden spoon to stir the salt until it dissolves.
  4. Allow the nuts to soak in the water on a counter for at least 12 hours. If you have the time to wait 24 hours, that’s even more ideal.
  5. Once the time has elapsed, dump the water down the sink. The water will likely be cloudy and otherwise contaminated, which goes to show how much mold you removed.
  6. Run the nuts under the tap or otherwise wash them in fresh water.
  7. Dry the nuts. Once they’re fully dry, you can store them in their original container or package. Besides eliminating mold, soaking nuts is beneficial in that it erases any traces of pesticides the nuts might contain. It’s also easier to absorb soaked nuts since the bioavailability of the nutrients within is more readily accessible in the body.

What Are Aflatoxins?

As promised, let’s next delve into aflatoxins, as they are a significant risk when consuming moldy nuts.

You’ll recall that aflatoxins are a type of mycotoxin. They too are fungal in nature and can damage a crop when it’s still in the field actively growing.

If not then, then crops can be affected at the harvest stage or during storage.

More than a dozen types of aflatoxins are out there, with four being identified as the most dangerous. They are G1, G2, B1, and B2 aflatoxins.

So what causes aflatoxins in nuts? Incorrect storage of the nuts before being packaged and sold is one contributing cause.

High temperatures and humidity can also ramp up the rate of aflatoxins in some crops, as can damage from insects and periods of drought.

In many countries, officials are supposed to check for the presence of aflatoxins while the nuts are being produced but not yet put on the market.

Some level of aflatoxins is allowed, around 20 parts per billion or ppb.

At that level, you’re not going to experience adverse effects when consuming aflatoxins, especially those effects that can cause cancer and otherwise damage the liver.

If nuts have more than 20 ppb of aflatoxins though, then the levels are considered dangerous, and the nuts should not be sold for consumption. 

How Do I Know If My Nuts Have Aflatoxins?

You had never realized that nuts could be sold on store shelves when moldy. Now that you’re aware, you’d like to avoid aflatoxins for the health of yourself and your family.

In that case, then limit consumption of the following nuts, which are known to contain greater levels of aflatoxins than most.

Brazil Nuts

Although Brazil nuts are lauded for health benefits such as improving brain, heart, and thyroid health and reducing inflammation, and as much as they are a good source of selenium, they’re also a significant source of aflatoxins.

At least the selenium content can kind of offset the damages caused by the mycotoxin.

Selenium can improve one’s cancer resistance, which means that a liver cancer diagnosis in the future just may be less likely even when eating Brazil nuts.


Although not the most aflatoxin-containing nut, pistachios are known for their high levels of B1 especially.

Of the four aflatoxins that are dangerous for human health, B1 causes the most egregious damage, so its consumption should absolutely be minimized.

The levels of B1 aflatoxin in pistachios should not exceed 8 ppb. The total level of acceptable aflatoxins in pistachios is 10 ppb.

Although spending more money on pistachios might not be the most appealing proposition, it can ensure the nuts are in better condition. When pistachios are grown in a proper environment, the risk of aflatoxin infection is reduced.

Here’s another tip. If you notice that some pistachios you’ve unshelled are not the trademark bright green, skip eating those nuts. Aflatoxins will discolor the nut.


By far, the biggest culprit when it comes to aflatoxin levels is the humble peanut.

Peanuts are riddled with B1 aflatoxins. The allowable level of that aflatoxin in peanuts is 2 ppb per kilogram. The same serving size of peanuts should not exceed 4 ppb of overall aflatoxins.

Like pistachios can be noticeably discolored if they’re especially moldy, the same applies to peanuts.

Rather than blindly grabbing them by the fistful and snacking, it’s worth taking the time to check each peanut you eat whether they’re pre-cracked or you bought them shelled and will crack open the nuts yourself.

Which Nuts Are Mold-Free?

If you want to make the safest shopping decision for your family, embracing organic nuts is best.

The standards used to produce organic nuts reduce their rate of mold compared to non-organic nuts.

That’s not to say these nuts will be entirely mold-free; the only way to be sure of that is to soak your nuts.

Organic nuts are low-mold enough that you and your family can breathe easier and enjoy more of nuts’ many health benefits.

Do Roasted Nuts Have Mold?

You’re well aware that soaking nuts can reduce their propensity for mold, but what about roasting nuts instead? Does roasting increase or decrease the likelihood of mold on nuts?

To answer that question, let’s assess the results of a 2014 study published in a microbiology journal.

The study reviewed 100 samples of nuts, including pistachios and peanuts, that underwent roasting.

Another 300 nut samples were collected with peanuts, walnuts, and pistachios that hadn’t been roasted.

The study concluded that the roasted nuts contained 14 percent more mold and that the fungal contamination rate was 18 percent higher.

Do keep in mind that this study only sampled nuts from Tabriz, Iran, and thus cannot be applied blanketly across other parts of the world.

Even still, the results don’t bode well for roasted nuts. They are quite likely to contain mold.

Can Moldy Nuts Still Be Eaten?

Even if the levels of aflatoxins are closely monitored before nuts are placed on store shelves, eating moldy nuts can carry with it some negative health consequences.

At the very least, you could experience abdominal pain and vomiting, especially if you ingest large quantities of aflatoxins.

These symptoms are your body’s way of telling you to stop.

Eating huge quantities of mold-infested nuts could lead to acute poisoning, says the World Health Organization.

The symptoms may include gallbladder hemorrhages, centrilobular zone necrosis, and generalized hemorrhages.

Aflatoxicosis is a life-threatening condition that, even though it may be more common in livestock than humans, requires immediate medical intervention.

Ingesting aflatoxins possibly elevates one’s risk of cancer, specifically, liver cancer. Other liver damage can also follow, especially in people that already have compromised livers, such as those living with hepatitis B.


Nuts are usually contaminated with mycotoxins such as aflatoxins due to long-term storage before the nuts are packaged and sold.

While mold infestation sometimes causes nut discoloration, it isn’t always as easy to pinpoint mycotoxins as that.

Nuts such as peanuts, pistachios, and Brazil nuts contain the highest level of aflatoxins, but other nuts could be moldy as well. Soaking nuts before consumption is your best option for removing mold.

After all, nuts are largely positive for our health and shouldn’t be omitted from a balanced, nutritious diet. Everything in moderation!

Chris Walker

Chris Walker has struggled for several years with mold after buying his own property. After finding the solutions to several issues around his home, he decided to create this site in order to answer as many questions about mold and mildew as possible to help others dealing with the same problems.

Recent Posts