I stumbled across this blogpost which claims that coffee is awesome for our bodies but only if it doesn't have mycotoxins (toxins generated by fungi).

To quote them:

One study showed that 91.7% of green coffee beans were contaminated with mold. This is before they were processed, which allows even more mold to grow. Another study showed 52% of green coffee beans and almost 50 percent of brewed coffees are moldy. Coffee is easily one of the largest sources of mycotoxins in the food supply.

They conveniently sell coffee beans that underwent a different process and don't have mycotoxins, so I have to wonder if this is a real problem and if there are ways to avoid it besides buying from them.

Perhaps buying green beans and processing them somehow so the fungi are washed away?

  • I think that the "should I avoid" part is off-topic. We don't do health-related recommendations here. But if you are convinced that the fungi are there and have decided to avoid them, the rest is on-topic. So a rewording will probably be good. – rumtscho Dec 21 '11 at 18:40
  • @rumtscho, I don't read it as "Should I avoid them?" but "Are their statistics true?" Whether that's on-topic or not, I'm not sure. – Peter Taylor Dec 21 '11 at 22:50
  • @PeterTaylor if he writes "should I avoid them", but means something totally different, then I still recommend a rewording. – rumtscho Dec 21 '11 at 22:57
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    The fact that this guy egregiously misquotes/misinterprets the second study - which was clearly designed to test the effects of roasting, not categorize the prevalence of mold - makes the post highly suspect. The fact that the so-called "brain fog" is part of a well-documented list of caffeine withdrawal symptoms and is also observed in heavy drinkers of tea and other caffeinated beverages moves the whole thing pretty deep into bunk territory. Seems like just another snake oil pitch to me. – Aaronut Dec 22 '11 at 1:56
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    It's also worth mentioning that the symptoms of mold exposure are far more varied and more serious than just feeling "edgy" and "cranky". If this were a serious problem then a lot more people in the world would be very sick. So again, I call BS. – Aaronut Dec 22 '11 at 1:59
up vote 39 down vote accepted

Time to apply a bit of healthy skepticism here:

The blog post:

  • Is (so far) the first and only one I've ever seen stating mold to be a practical problem in coffee - in the sense of being present in a high enough quantity to matter (mold grows everywhere).
  • Uses all kinds of weasel words to describe symptoms ("edgy", "cranky", "useless mentally").
  • Describes symptoms that are well in line with plain old caffeine withdrawal.
  • Frequently links to other blog posts on the same site, most of which are "top 10 ways" and "top 5 reasons" fluff pieces.
  • Manages to cite and thoroughly misuse two studies: one from 1995, and another from 2003. Both are about Ochratoxin A (OA), which isn't even the biggest risk; Aflatoxin is. (More on these later).
  • Advertises a fairly expensive product, sold by the same author.

The author:

  • Is, according to his LinkedIn profile (which I refuse to link here), the VP of Cloud Security at Trend Micro - a Silicon Valley tech company. I could not find any evidence that he or his his employer has any experience in human biology or nutrition.
  • Makes all sorts of unusual claims about himself: "He upgraded his brain by >20 IQ points, lowered his biological age, and lost 100 lbs without using calories or exercise."
  • Has an entire page of testimonials, which he frequently cites as "evidence".
  • Has an entire site dedicated to product-peddling, including the ubiquitous six-second abs (yes, that's hyperbole) and a $60 "earthing mat".
  • Has the following disclaimers on the product site (all in tiny print at the bottom):

    The statements made on this website have not been evaluated by the FDA (U.S. Food & Drug Administration). Our products are not intended to diagnose, treat, cure, or prevent any disease.

    The information provided by this website or this company is not a substitute for a face-to-face consultation with your physician, and should not be construed as individual medical advice. The testimonials on this website are individual cases and do not guarantee that you will get the same results.

  • In short, he employs tactics which are commonplace among con artists selling magnetic bracelets. In my opinion, all his claims are technobabble, and I think they are not trustworthy.
The facts and studies:

  • The largest sample tested was just 60 samples of beans, and was tested from only one source (Brazil). This is fine for individual studies, but in the real world there are hundreds (thousands?) of sources from many different countries. It's safe to say that the current studies don't even come close to testing all of the coffee from around the world.
  • Both OA studies found an incidence rate of approximately 50% for the OA-producing mold, at wildly different concentrations (minimum 0.2 ppb in one study, maximum 7.8 ppb in another). If this tells me anything at all, it's that you should probably vary your source if you want to minimize your risk.
  • Neither the FDA nor the EFSA actually have a legal limit for OA, but the EFSA "suggests" a limit of 8 µg/kg, which means that even the worst samples are below the very conservative legal limit.
  • One study actually tested the incidence of OA in brewed coffee, not just the beans, and found a maximum of 7.8 ppb in the brew (that's 7.8 µg per 1 kg of ground coffee).
    • For reference, there's an EFSA directive recommending an intake of no more than 120 ng/kg (body weight) per week, which comes out to 8.4 µg/week for a 150 lb/70 kg individual, or 1.2 µg/day.
    • Based on the worst contamination of brewed coffee (7.8 µg/kg), doing the math, you'd have to consume the brew from 150 g of ground coffee per day. That's about half a standard-sized tin of coffee. Per day. If you drink that much coffee, shame on you.
  • The 3rd study (the one rumtscho linked to, not cited by the blogger/con artist) looked at Aflatoxin, not Ochratoxin, which actually is regulated by the FDA at a maximum of 20 ppb. This study also showed approximately a 50% incidence rate after roasting, with the highest concentration of AT being 16 µg/kg for decaf (less with caffeine). So that means with any random cup of coffee you have up to a 50% chance of consuming an amount of AT that's still well below the FDA limit - that's very nearly zero risk.
  • None of the studies test the rate of mold growth on beans while in storage under various conditions (temperature, humidity, etc.), so we can't comment on what happens in storage. So I guess if you want to really be on the safe side, only buy as much coffee as you think you can use in a week or two.


Don't believe everything that people tell you - especially people with something to sell. Unless you're drinking gallons of coffee a day, brewed coffee is perfectly safe.

  • Awesome synopsis, thank you very much! I feel safer now :) – w00t Dec 26 '11 at 10:20
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    As the blogpost author complained that the "about the author section" contains personal attacks, I edited it. Now it only contains verifiable facts, such that he has a site which sells an earthing mat. I changed the "con artist" accusation to refer to the (publicly visible) tactics employed by the blog post author and not to his (unobservable for us) person, and pointed out that this is Aaronut's personal opinion. I hope that this dials back the tone while keeping all the objective points @Aaronut intended to make. – rumtscho Jun 24 '12 at 15:16
  • The short answer would have been 'no, it's not a significant problem, otherwise the FDA and other health organisations would have regulated around it'. But your answer is pretty neat :-) – BaffledCook Jun 24 '12 at 16:15
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    @BaffledCook: I think it was necessary to address the underlying issues, because part of the author's claim is that the FDA regulations somehow aren't good enough or are based around economics rather than safety (which is a preposterous claim by itself given the FDA's well-earned reputation as a wet blanket, but there you have it). – Aaronut Jun 24 '12 at 21:19
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    The question revolves around a specific blog post, not about an ongoing scientific study or even a notable claim, therefore the credibility of the author of the original blog post is a totally legitimate concern, and it's not at all unreasonable to devote a mere 25% or so of the post to addressing it. The language here has already been softened quite a bit; your suggestion is noted and declined, as I don't find your rationale at all convincing and don't know anything about your motives either. Feel free to discuss this further on Seasoned Advice Meta where it can be properly vetted by the community. – Aaronut Aug 18 '12 at 2:34

My university has access to the study @w00t linked in a comment here, so I thought I'll provide a summary of their findings.

  1. Do green coffee beans contain aflatoxins? They found that yes, coffee beans naturally grow molds which produce aflatoxins. Molds and toxins were isolated from 17 out of 30 samples of green coffee beans they purchased from local markets.

  2. Do roasted coffee beans contain aflatoxins? Yes, 22 out of 30 samples had molds and aflatoxins. The levels were lower than in green beans (about 30% less).

  3. Does roasting reduce aflatoxins? They tried three types of roasting (oven, microwave and traditional). All methods roughly halved the aflatoxins, with traditional roasting resulting in the highest reduction (55.9%). The difference between methods was very small, ranging from ~45% to ~55%.

  4. Does caffeine affect aflatoxin growth? They put caffeine and aflatoxin-producing molds in a mixture of sugar, yeast, and water, and waited. The molds grew with only half the speed of molds in the same mixture without caffeine added. They couldn't detect any aflatoxins in the mixture itself, but say this could be because they started with small amounts of mold. (Their measurement method is sensitive enough to detect tenths of micrograms per liter).

Conclusion: You can't get rid of mold and their byproducts (aflatoxins) in your coffee, but you can reduce them somewhat. If you insist on that, use freshly roasted coffee, no decaf. Be aware that the study doesn't give an answer if brewing coffee with moldy beans results in aflatoxins in your coffee. So you can't use it to arrive at a recommendation for safe coffee-drinking habits. Change them if you want to, but be aware that it will be a speculation. The question whether the alpha toxins are dangerous to human health, or which concentrations can be considered absolutely safe, is not researched in this study. Also, they found that while changing the roasting method does have an effect on the mold present in the beans, the difference was very small - so even if it has negative effects, I doubt that you can avoid them by changing the roasting method.

  • 4
    The study also mentions that the average for green (not roasted) coffee beans is 4.28 ppb, which is well below the FDA stated limit of 20 ppb. And then, as you mention, there's the obvious question of how much of that gets into your brew (clearly not all of it). The risk sounds vanishingly small to me, unless you already have a hypersensitivity to mold (in which case coffee isn't the only thing you should be avoiding). – Aaronut Dec 22 '11 at 15:49
  • @rumtscho thanks for your sleuthing :) – w00t Dec 26 '11 at 10:27

Perhaps we should re-direct this conversation to be closer with the OP's intent. The OP's question is:

"if this is a real problem and if there are ways to avoid it besides buying from them"

The first question can be paraphrased as "Do mycotoxins present in brewed coffee affect mental and physical performance enough that I should spend extra money to buy mycotoxin-free beans?".

First off, the question is highly subjective - is a potential increase in mental performance worth the extra money to the OP?

There are no studies on is whether the level of mycotoxins present in coffee has any measurable effect on a person's mental and physical performance. Asprey has a theory based upon personal experience, therefore they may be worth something, but should also be taken with a grain of salt. The lack of studies on this does not mean Asprey is a fraud or a con-artist, only that his assertions should be taken for what they are - personal experience. His opinions should not be dismissed out-of-hand.

We therefore have to break the question down. Does mold exposure impact mental performance?

As far as I know, there are no easy answers here, but this study does imply a link between mold exposure and mental performance:


Second, does the level of mold / mycotoxins present in coffee affect mental performance? There are no studies about this, so your only source will have to be the personal experience of people trying this for themselves (aka Asprey and his readers).

Separately, the moderators and other contributors have made it clear that the mycotoxins present in coffee (beans or brewed) fall under the FDA's limits. However, Asprey's blog and assertions are about maximizing mental & physical performance. There may very well be a different threshold between what the FDA considers a "safe" level of mycotoxins, and the level of mycotoxins capable of affecting your mental performance. It would be illogical to conclude that the two thresholds are the same. Keep in mind that the degree of change Asprey is likely talking about may be the difference between getting an A+ vs. an A on whatever measure you consider to be relevant.

In short, there are no hard & fast answers to the OP's question because no relevant studies exist. We can safely say that yes, mycotoxins are present in coffee. Do said mycotoxins affect mental performance? Unknown, but it is supported / suggested by anecdotal evidence. Is anecdotal evidence sufficient for the OP to spend extra money on coffee beans? This is the real question.

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    How much of that study did you read? First of all, it's not an experiment, just an analysis. Second, it deals with much higher levels of exposure than has ever been shown to be possible from coffee. Third, it generally deals with a very different type of mold. Fourth, there are several references to significant physical symptoms (headaches, dizziness, etc.) These were people who had serious problems, to the point where they were actually involved in litigation. Nothing to do with coffee, and there is an easy answer: we reject anecdotal evidence until verified by an experiment. – Aaronut Dec 28 '13 at 0:37
  • Even if these studies did exist, discussing them would be completely off topic on our site. We do food safety stuff here, as in "will you go into hospital within 2-3 days of eating this", but not "healthy" food in the sense of what long term effects a food may or may not have on your physiology. – rumtscho Dec 28 '13 at 7:53
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    I think this is an attempt to answer the question, so I'm going to leave it, but I'm not sure it's a particularly useful one - as others have said, there's basically no evidence here, and no reason to assume or speculate that there's anything to worry about. – Cascabel Dec 29 '13 at 16:10
  • For the record, anecdotal “personal experience” should generally be dismissed in light of scientific studies. – user52649 Sep 23 at 11:57

The take away is not all coffee is created equal try different beans until you find one that gives you the best bang for your buck, Starbucks dark roast puts me in a better mood than foldgers or Maxwell house. Mycotoxin ? Branding? Subjectivity?

It's very possible that unnamed blogger / coffee and supplement salesman has a sensitivity to mycotoxins.That people who regularly consume healthy fungus and bacteria aren't normally affected by.

Or it could be that other chemical components of the coffee influenced by the growing region that are best suited to his physiology.

We don't know what the real reason is , we can assume much of the coffee available to us is perfectly safe , with the exception of all that toxic caffeine stuff sometimes called a phytotoxin!!!

I'm the guy who made this coffee. In my opinion, yes, alfatoxins are dangerous for you, and you should drink coffee which doesn't have them. Most coffee gives me awful symptoms, ones so bad I quit coffee for 5 years before I figured it out. Now I only drink this coffee, because it gives me no symptoms, and I am selling it because I believe it is better for others too. My opinion is that

There are toxins (specifically biogenic amines and mycotoxins) present in coffee at levels high enough to affect how you feel.

Am I saying coffee will kill you? Nope. But bad coffee slows you down - a lot - and low toxin coffee speeds you up - a lot.

To back this opinion, I am currently conducting an IRB-approved study, with Stanford University's assistance, to test the mental performance of people on my Upgraded Coffee vs Starbuck's dark roast. I can also invite you to test the toxin-free coffee for yourself, by purchasing it from me or from other sources (I wrote a blog post "How to find high performance coffee in your city", google it).

My other sources for my opinion are

  • This study. It shows detectable aflatoxin in 85 of 127 samples. Some (many) were below the legal limit, but the problem is that the legal limit is not the safe limit, it's the economically feasible one.
  • This conference talk. It says that coffee can contribute up to 25% of your daily "safe" (not by my standards) dose of the OTA toxin.
  • If you google "coffee mycotoxin" you can find many other studies which have shown the presence of mycotoxin in coffee.

Aaronut's answer suggests that I am not qualified to judge whether coffee with alfatoxins is dangerous. I feel that his "The author section" is an example of "attacking the messenger", which is a poor tactic. Here are my credentials:

  • I'm a very successful Silicon Valley exec with enough money that I don't need to con people at all.
  • I run an anti-aging group that brings world-class experts in every month.
  • My wife is an MD and co-author of my book on nutrition for pregnant women (currently in publishing)
  • I've lectured internationally on human performance
  • 100 000 people a month read my blog
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    If you want to question my facts, or criticize my reasoning, that's perfectly fine to do as a comment, but as an answer this (a) contributes nothing of substance and (b) is dangerously close to being spam since, among other things, you're telling people here to spend money on your product while continuing to make vague unsubstantiated claims, handwave away the decades of scientific study that went into the creation of food safety regulations, and even disclose the hypothesis of an unfinished study which is a gross ethics violation (since this type of study would need double-blind controls). – Aaronut Jun 24 '12 at 11:31
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    In short, if you want to keep this answer up here, I suggest you do some substantial clean-up on it. Eliminate the subjective health claims and sales tactics, which unfortunately are almost the entire post. – Aaronut Jun 24 '12 at 11:32
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    @Aaronut: I think it's safe to delete this answer on grounds that it isn't in fitting with tone for the site (personal attacks, sales tactics), nor is it informative. – BobMcGee Jun 24 '12 at 13:23
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    Personally, I don't agree with your opinion, and your arguments and list of credentials don't convince me. In my role as a moderator, I tried to be as neutral as possible and edit the post in a way which presents you in a positive light, the way you would have done it. In my role as a community member, I stand by my downvote and will not remove it, because I think your opinion about coffee is wrong, and the arguments you list don't convince me. – rumtscho Jun 24 '12 at 15:02
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    Likewise, I'm fine with the edited form of this answer and won't delete it; however, it remains an exceptionally poor defense due to the fact that none of the cited sources actually substantiate the claim that "typical" coffee contains dangerous amounts of aflatoxin or ochratoxin, nor do any of the cited credentials lend any credibility to the author as an expert on mycology or even coffee in general. We don't know if your specific claims are supported by these "world-class experts" (or even who they are), and "human performance" is not a scientific field. – Aaronut Jun 24 '12 at 21:16

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