Yes, almonds can and do get moldy. Every batch of almonds carries fungal spores picked up in the orchard or during harvest, and those spores will grow into visible mold whenever the nuts are exposed to enough moisture. Under proper storage conditions almonds stay safe and shelf-stable for years, but a forgotten bag in a humid pantry or a container that wasn’t sealed well can turn them into a breeding ground for mold, including species that produce harmful toxins.
Which Molds Grow on Almonds
A study of California almonds found black-spored Aspergillus species on 100% of samples tested, followed by Penicillium molds on about 58% and Cladosporium on roughly 53%. These are the same broad families of mold you’d find on bread or fruit, and most are relatively harmless nuisance fungi. The real concern is a subset called Aspergillus flavus, which was also isolated from almonds in the study. This particular mold produces aflatoxins, a group of toxic compounds strongly linked to liver cancer with long-term exposure.
Mold spores sit dormant on the surface of almonds as long as the nuts stay dry. The moment moisture levels rise, even temporarily, those spores can activate and begin growing. That’s why a single episode of condensation inside a storage bag or a humid stretch of weather in an unsealed container is enough to trigger a problem.
The Aflatoxin Risk
Aflatoxins are the main health concern with moldy almonds. Produced primarily by Aspergillus flavus and a related species called Aspergillus parasiticus, these toxins are colorless and tasteless at low levels. Chronic exposure is associated with increased liver cancer risk, according to the National Cancer Institute, though no outbreak of aflatoxin-related illness has been reported in the United States. That’s largely because the FDA treats any food containing more than 20 parts per billion of total aflatoxins as adulterated and subject to seizure or import refusal.
Climate trends may be shifting the risk profile. Research suggests that rising temperatures and drought conditions favor the growth of more toxin-producing strains of Aspergillus on almonds. As almond-growing regions get hotter and drier, the balance between low-toxin and high-toxin fungal populations could tip in a less favorable direction.
How to Tell if Almonds Have Gone Bad
Mold on almonds isn’t always obvious. Visible signs include fuzzy white, green, or black spots on the surface, but contamination can also happen at levels too small to see. Here’s what to watch for:
- Appearance: Discoloration, dark spots, or any fuzzy growth on the surface. Raw almonds that have gone bad may look identical to good ones from the outside, making visual inspection unreliable on its own.
- Smell: A musty, sour, or paint-like chemical odor. Fresh almonds have a mild, slightly sweet scent. Anything sharp or off is a warning sign.
- Taste: Bitter, sour, or otherwise unpleasant flavor. One food chemist at UC Davis described bad almonds as so unpleasant that “you’ll take a couple of chews on them, and you’re spitting them out.” If that happens, discard the batch.
- Texture: Almonds should snap cleanly. A rubbery, soft, or shriveled texture suggests moisture damage, which means mold may not be far behind.
Rancidity and mold are different problems, but they often show up together. Rancidity is the breakdown of fats from exposure to heat, light, or air. Mold is fungal growth from moisture. Both make almonds taste terrible, and both are reasons to throw them out.
Can You Save Moldy Almonds by Washing or Roasting?
Not reliably. Washing and roasting can reduce aflatoxin levels, but they don’t eliminate them completely. Roasting at high temperatures (roughly 90 to 150°C for 30 minutes or more) has been shown to reduce aflatoxin concentrations in nuts by 57 to 93%, depending on the type of nut and conditions used. Washing can remove even more, up to 90 to 97% in grains, partly by stripping away contaminated outer layers.
Those numbers sound encouraging, but there’s a catch. If aflatoxin levels were very high to begin with, a 90% reduction still leaves a meaningful amount behind. And since you can’t measure aflatoxin levels at home, there’s no way to know whether what remains is within safe limits. The practical advice is simple: if almonds look or smell moldy, discard them. Trying to salvage them isn’t worth the risk.
How to Store Almonds to Prevent Mold
The Almond Board of California recommends storing almonds below 50°F (10°C) and below 65% relative humidity. Under those conditions, whole natural almonds maintain quality for up to two years. A U.S. Army shelf-life study found that almonds packed in vacuum-sealed foil pouches lasted three years across multiple forms, including raw, roasted, blanched, and sliced.
For most people, that translates to a few practical steps. Keep almonds in an airtight container, ideally in the refrigerator or freezer. A sealed glass jar or heavy zip-top bag with the air pressed out works well. Avoid leaving them in a warm pantry, especially during summer, and never store them in a container that allows condensation to form. If you buy in bulk, divide almonds into smaller portions so you’re not repeatedly opening the same large bag and introducing humid air.
Commercially sold almonds in the U.S. have an extra layer of protection. Since 2007, the USDA has required pasteurization of raw almonds before sale. Common methods include steam treatment (heating to about 93°C for 65 seconds) and fumigation with propylene oxide, though the latter is banned in the European Union. These treatments target bacteria like Salmonella rather than mold specifically, but they do reduce the overall microbial load on the nut’s surface. Pasteurized almonds are still labeled “raw” because the process doesn’t roast or visibly change them.
Pantry vs. Fridge vs. Freezer
Where you store almonds makes a significant difference in how long they last. At room temperature in a sealed container, almonds typically stay good for several months but begin to lose freshness and develop off-flavors faster, especially in warm or humid climates. Refrigeration extends quality well past a year. Freezing extends it further, and almonds freeze well without significant changes in texture or flavor.
The enemy is always moisture. Even cold storage can cause problems if the container isn’t sealed properly and condensation forms when you move it in and out of the fridge. If you freeze almonds, let them come to room temperature inside the sealed container before opening it. This prevents warm, humid air from condensing on the cold nuts.