Wow, I could get a Ph.D. just on this topic alone! There is just so much research on mold in nuts and my nerd brain is both so excited and overwhelmed. So let me just state that this is a very simplified review of what I discovered after some digging around in the research literature. Even though I have a PhD and am well versed in understanding sound research, I am not an expert on fungi or their biology. That being said the information and suggestions in this post are based on scientific facts and published papers.
If you are here just for the solution and not the nerdy stuff let me just leave this here… mold sucks, mycotoxins are worse. While most nuts will be contaminated with mold this does not mean they have mycotoxins present. If you take nothing else from this post it is this, PICK OVER, RINSE, HEAT, STORE your nuts and seeds! Becuase Mold in nuts sucks! (oh and for a creamy almond milk recipe, click here)
OK let me start by stating that I eat, and will continue to eat, grains, seeds, and nuts even after writing this post. I am not going to try and freak you out or convince you that you shouldn’t eat food and that everything is going to kill you. That’s just not helpful for anyone! I didn’t discover that the food industry is trying to poison us or has some cover-up scheme. What I found was quite the opposite, there is a lot of research going on behind the scenes addressing this issue. Actually, the intended purpose of this article is to inform you of the dangers of consuming nuts that have been improperly handled and stored and the steps you can take to correct any mishandlings and safely store your food.
I started looking into this when I came across an article one day, ironically when I was eating some oatmeal slathered with peanut butter. The article stating that tree nuts, seed, and grains can foster various microorganisms including toxigenic and pathogenic fungal species, AKA MOLD! Removing the spoon from my mouth and ending my morning meal I tried not to freak out and while I quickly hit up goggle… after coming to the same conclusion that goggle is not my friend, I went on to read some actual facts published by real scientists regarding mold infestation in our precious peanut butter!
Before I delve into what I found let me just clear up some terminology so we can all be on the same page. Mold (or mold) is a fungal species that require moisture to grow and organic material to produce energy. While there are over 100,000 types of mold spores, some of them can synthesize (or make) mycotoxins when under the right condition. When these conditions are met, fungi proliferate (or grow) into colonies and mycotoxin levels become high. While mold on its own can have detrimental effects on our health, the mycotoxins they produce are actually poisonous to humans. Their long term effects include cancer and immune deficiency problems too name a few.
The fungi that produce mycotoxins in food fall into 2 groups: those that invade before harvest (field fungi), and those that invade after harvest (storage fungi). The field fungi disappear after harvest if handled correctly by the producer (by drying them). So field fungi, in theory, should not concern us because we are going to assume that our food is handled properly by the food producer and manufacturer. So what is partially in our control (because this also applies to grocery store shelves and bulk bins) is the storage fungi. That is the fungi we want to eliminate. Fungi growth in this state depends on physical factors, such as moisture (water activity), temperature, and damage as determining factors of whether storage fungi will make an appearance. So these are the things we need to address. But first the low down on mycotoxins…
While there are many types of mycotoxins, there are 5 groups that occur in food, deoxynivalenol/nivalenol; zearalenone; ochratoxin; fumonisins; and aflatoxins. The table below summarizes some of the places they are found and their effects on our health (it is not a complete summary by any means and is missing many nuts and grains but you get the idea). Fumonisins and aflatoxins are of the greatest concern to our health and the most present in grains and nuts (Tournes et al., 2015). Aflatoxins were classified as a class 1 carcinogen by WHO, and interact with the function of the immune system, disrupt the digestive and urinary system, the reproductive systems, nervous system, are mutagenic in bacteria (affect DNA).. pretty much they suck!! Now before you dismiss this mycotoxin as rare let me just state that many of the research I read found positive results for Aspergillis, the mold that produces this toxin, when testing nuts for fungi. Meaning those beloved nuts you eat every day has the potential to make you seriously sick!
I do not need to sell you on the harmful effects of mycotoxins, most people get that they are bad and want to avoid them. So before I freak you guys out anymore I want to say that although mold produces mycotoxins, they are not always a packaged deal. So despite all the terrifying blogs and fear-mongering going on just take a breath. Remember, as I said above in order for mold to produce mytotoxins the right conditions need to be met. In fact, despite the vast reports of positive mold samples from grains, nuts and seed (Abdel-Gawad et al., 1993, Tournes et al., 2015, Jiménez et al., 1991), positive mycotoxin levels are much less common (Abdel-Gawad et al., 1993). But this is not a green light for enjoying your raw nuts. Rare does not mean zero and we still have the mold spores to deal with! Mold on its own can make you very sick! But the main idea is we want to eliminate the possibility of having food that ‘may’ contain or eventually produce mycotoxins! Aka remove the mold issue so there is no chance of encountering mycotoxins!
Alright now for some scary before the solution, hang in there with me. The main conclusion I got from researching mycotoxins is that they are almost impossible to eliminate once a portion of food is contaminated with them. However, most of the contamination seems to occur in the field, before the product goes to market and the contaminated food is discarded. While our food organizations regulate the number of acceptable mycotoxins in foods that go to the market, the detection is problematic because aflatoxins are not evenly distributed throughout a bulk shipment. Actually according to the USDA ” aflatoxins are considered unavoidable contaminants of food and feed, even when good manufacturing practices are followed”. Whaaaaa, ya no thanks! You know it’s times like these that I thank my stars that I am vegan. I won’t even go into the number of mycotoxins in animal feed and cow milk, guys it is scary!! So I know one HUGE way I am reducing my exposure is by eliminating animal products (for this and sooo many other reasons, you know sentient beings and all).
So what can we do about this, well we know that heat treatment works on mold spores, BUT mycotoxins can not be destroyed by heat. Research on the removal of mycotoxins during food preparation found that cooking, frying, and roasting were unsuccessful at removing mycotoxins from food. In fact, Kaminmura concluded that even after boiling at 100-120 degrees C for 45 minutes the number of mycotoxins remained at 100%!!!! That’s because the decomposition temperature of Aflatoxins is 237-306 degrees Celsius (Jalili 2015). While some methods may be better then others (pressure cooking rice can reduce mycotoxins by 78-88 percent) the main conclusion is that the removal of mycotoxins depends on many factors and is extremely hard to eliminate fully. So the biggest thing we can do is eliminate and remove any storage fungi to reduce the POSSIBILITY of mycotoxins growing on our food. This means you want to buy fresh nuts, seeds and grans from a trusted company and store them properly, sorry bulk barn! While this still won’t address possible mycotoxins that may be present in our food this is a huge start. We can not live life fearing food, our bodies are very good at detoxing and eliminating waste. If you are healthy and have good functioning detox pathways (gut, liver etc) then the odd trace exposure isn’t going to kill you or make you sick. The issue arises with large or chronic exposure. In the end, if you are concerned then do not make nuts, seeds, and grains a huge part of your diet. This falls in line with having a well balanced whole food diet anyways!
Without going into to much detail and making this a review paper rather than a blog post what I found was that when researchers tested samples they almost always found some contamination of mold. The percentages and amount of mold they see vary with each paper and each nut but the general idea is that you can almost guarantee you will find some species present. As for which nuts are the worst, it seems like walnuts, peanut, pine nuts, almonds, and cashews rank high on the board. Tournes er al., (2015 ) found Aspergillus (the mold that can produce the mycotoxin aflatoxin) in all the nut samples he tested, with walnuts and pine nuts testing the highest for both mold and yeast. But remember, mold does not mean mycotoxins, yet!
Fungi can not grow or produce mycotoxins in dry foods. So drying will be your best friend here and this extends to how you store your nuts and grains after you dry or cook them as well. Moisture is your enemy. The great news is that mold is killed by heat so the removal of mold is actually very simple. Rinse, then cook or heat to dry!
You also want to pay attention to any physical damage as this is a contributing factor to storage fungi. If there is damage to the nut then moisture can get deep within making it harder to fully dry. This is a huge concern for nut butter because let’s face it companies will more likely use the damaged nuts at the bottom of the barrel that is too ugly to package and sell. While I was not able to find any research on the presence of mold in nut butter despite this idea I still feel safe consuming butter. Many brands use dry roasted nuts and seeds and or pasteurization which in theory should destroy any mold present. Plus these nuts and seeds should be fresh which further reduces the possibility of mycotoxins.
OK, so what can we do at home to help reduce our exposure to mold (and possibly mycotoxins) from nuts, seeds, and grains? Here are a few of the procedures suggested by researchers that we can implement fairly easily:
1. Handpicking: Carefully inspect your grains and nuts for signs of mold and discard any that look moldy, discoloured or shriveled. Some additional steps you can take are to buy grains and nuts as fresh as possible, ideally from a local and trusted brand. Reach out to the company and ask them what their procedure is for testing for mycotoxins, how they prepare and select the nuts and if they pasteurize.
2. Rinsing and soaking: This information was harder to come by but the overall conclusion I found was that washing can reduce mold and water-soluble mycotoxins by 65-69 percent in some foods. Without boring you to death, the take-home is that this is a good step to take even though it won’t eliminate or deactivate all the mold or mycotoxins that may be present. Researchers concluded that soaking in a 0.1 M solution of water and sodium carbonate for 24-72 hours seems to be the best practice for your chance of eliminating the most amount of mold. However, they also conclude that a simple water rinse is effective at reducing mold spores. Since the research on this is scarce, recommendations of soaking times per nut or grain just doesn’t exist yet. And while there are countless blog on the recommended soaking times for nuts, seeds and grains (link here )(and here), I believe these guidelines are based on soaking for the purpose of increasing the nutrient bioavailable (activating them) or reducing phytic acid and not for mold reduction.
HUGE caveat here, I will need to do some more research on this but my understanding is that too much water is not a good thing. This is a wake-up call for me because just before writing this I soaked my cashews for like 24 hours… oooops! Remember mold loves moisture! So make sure to under soak rather then over soak if you are concerned and rinse a lot! The real mold reducer will be heat treatment, aka dehydrating or cooking.
3. Dehydrate: while mycotoxins are heat resistant this will be an important step to reducing mold spores and their ability to proliferate. Remember mold loves moisture so you want to eliminate as much moisture as possible! Again the procedure for dehydrating nuts, seeds, and whole grains are well published (like here). I wouldn’t worry much about the exact procedure but more on getting them as dry as possible! 12 hours at 150 degrees seems like the gold standard.
4.Proper storage: After buying good quality nuts, seeds and grains, picking thru, rinsing and drying make sure to not undo your work! You will want to continue to minimize exposure to moisture, temperature fluctuations, and damage. If possible store them in a glass jar in the freezer or a cold dark place.
So the biggest take away is to rinse (or soak) and DRY your nuts, seeds and when possible grains. So that is it for now if you made it this far thanks for reading. There are also debates and research going into nut allergies and mold but that would be for another post. If you are interested in that leave a comment below!
PICK OVER, RINSE, HEAT, STORE
You will also find these nuts and seeds make the best plant-based milk. For a great recipe on making creamy almond milk check out this post, Creamy Almond Milk.
Abdel-Gawad KM1, Zohri AA.(1993) Fungal flora and mycotoxins of six kinds of nut seeds for human consumption in Saudi Arabia. Mycopathologia. Oct;124(1):55-64.
Burge, H. How does heat affect fungi? Bipolaris species https://www.emlab.com/resources/education/environmental-reporter/how-does-heat-affect-fungi-bipolaris-species/
Kamimura, H. (1989). Removal of mytotoxins during food processing. Mycotoxins and Phycotoxins ’88, Amsterdam: Elsevier Science Publisher pp 169-176.
Karlovsky, P., Suman, M., Berthiller, F., De Meester, J., Eisenbrand, G., Perrin, I., Dussort, P. (2016). Impact of food processing and detoxification treatments on mycotoxin contamination. Mycotoxin Research, 32(4), 179–205. http://doi.org/10.1007/s12550-016-0257-7
Jiménez, M., Mateo, R., Querol, A., Huerta, T., Hernández, E..(1991) Mycotoxins and mycotoxigenic moulds in nuts and sunflower seeds for human consumption.
Locksley. Trenholm, H & L. Charmley, Lynne & B. Prelusky, Dan & M. Warner, Robert. (1992). Washing procedures using water or sodium-carbonate solutions for the decontamination of 3 cereals contaminated with deoxynivalenol and zearalenone. Journal of Agricultural and Food Chemistry – J AGR FOOD CHEM. 40. 10.1021/jf00023a021.
Mahoney, N. and Molyneux, R.J., 2004. Phytochemical inhibition of aflatoxigenicity in Aspergillus flavus by constituents of walnut (Juglans regia). Journal of Agricultural and Food Chemistry 52: 1882-1889.
Tournas, V., Niazi, N., & Kohn, J. (2015). Fungal Presence in Selected Tree Nuts and Dried Fruits. Microbiology Insights, 8, 1–6. http://doi.org/10.4137/MBI.S24308
World Health Organization (2018) Department of food safety and zooness. Foodsafety Digest WHO/NHM/FOS/RAM/18.1 (http://www.who.int/foodsafety/FSDigest_Aflatoxins_EN.pdf)