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A question on Cooking SE brought up the fact that:

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. SOURCE

The studies quoted by the answer indicated that there might be some toxins that make it to the ground used in brewing coffee but did not address if there were any problems with toxins actually in the coffee.

I thought the question may be better addressed by our learned folks that share their knowledge and research here at Skeptics :)

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Chad
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    Green coffee is unroasted. Wouldn't several minutes of exposure to 400+F kill mold? At that point, the coffee is typically vacuum-sealed to preserve freshness. – Larry OBrien Dec 22 '11 at 22:51
  • Apparently, the idea is that the mold generates toxic chemicals (which aren't destroyed by heat) before it is roasted. Dave Asprey seems to think it's a big deal. I'm not sure myself... – Chris Hynes Dec 23 '11 at 02:51
  • and even if those chemicals exist in the roasted beans, that doesn't mean they survive the boiling heat when the coffee is brewed (or the chemical preservatives used to preserve the roasted beans during shipping). – jwenting Dec 23 '11 at 07:03
  • @ChrisHynes that's exactly how botulism works – Sklivvz Dec 23 '11 at 10:18
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    @Sklivvz Botox is quite [heat sensitive](http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2249394/pdf/epidinfect00011-0120.pdf); I thought the issue with *C. botulinum* contamination were the endospores which could survive cooking and cause problems in those with weak immune systems (babies and honey). Fungal toxins may be different though; it would really depend on their nature (protein vs. small molecule for one). – Nick T Dec 24 '11 at 06:44
  • I've heard from a friend who is a nutritionist that many (most/all?) mold spores can survive extreme heat. Thus reheating (even in a microwave) of moldy food does not make it safe. I don't have a source to quote other than my friend, though. And this does not directly address the issue of "toxins" (unless any mold spores themselves are toxic). – Flimzy Dec 24 '11 at 19:13
  • the claim is about aflatoxins (similar to mushroom poison), not spores. – Sklivvz Dec 27 '11 at 21:45
  • @jwenting - I Guess that was what I was hoping to answer with this question. Does some level of toxins actually survive the process of prep, roast, package, grind, brew. – Chad Dec 28 '11 at 14:17
  • @Sklivvz -- sure, but there are two questions here that I haven't seen proven. #1, are the mycotoxins killed by heat. #2, do mycotoxins in small amounts (parts per billion) actually have any effect on most people. I haven't seen convincing evidence for #2, at the least. – Chris Hynes Jan 10 '12 at 19:58
  • Actually safe does not mean has no effect. Just that it is not likely to kill you or make you extremely ill. It could have some minor effect like causing say a 5% loss in lifting ability for example. – Chad Mar 09 '13 at 02:52

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Well, the original study is behind a paywall, however from the abstract we can easily deduce that the incidence of toxins is only 33% and in those cases, it's within the EU safety limits.

In other words, there's nothing to worry about: you need a certain minimum concentration of mycotoxins before you can experience any effect.

Twenty samples (33.3%) of 60 were contaminated with the toxin at levels ranging from 0.2 to 7.3microg kg(-1). The average concentration was 2.38 microg kg(-1). All positive samples showed OTA levels below the limit suggested by the European Union (8 microg kg(-1)).

More sources:

  • EU legislation
  • FSA legislation

  • Major literature review on mycotoxins which specifies that chronic effects of aflatoxins (the mycotoxins specified in the claim) are associated with cancer, immunodepression and liver disease, but makes no mention of other effects:

    The data on aflatoxin as a human carcinogen are far more damning than the data implicating it in acute human toxicities. Exposure to aflatoxins in the diet is considered an important risk factor for the development of primary hepatocellular carcinoma, particularly in individuals already exposed to hepatitis B.

    It also mentions that, in industrialised countries, aflatoxin ingestion is "insignificant":

    In developed countries, sufficient amounts of food combined with regulations that monitor aflatoxin levels in these foods protect human populations from significant aflatoxin ingestion.

Sklivvz
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    I don't think Wikipedia is a good source for the claim of a minimum concentration of mycotoxins before they create an effect. It's the core of the claim of Dave Asprey who get's cited by Chad that small amounts of mycotoxins do have an effect. – Christian Dec 27 '11 at 15:01
  • @Christian added more sources – Sklivvz Dec 27 '11 at 15:32
  • I don't follow the "if it doesn't reach a lethal dose" there no effect argument. Nobody claims that there are enough toxins in brewed to kill people directly. Dave Asprey claims that the toxins have an effect in reducing mental and physical performance. – Christian Dec 27 '11 at 19:08
  • @Christian I provided a better quote, it wasn't clear :-) – Sklivvz Dec 27 '11 at 19:54
  • @Sklivvz - But your source says that 20 of 60 "were contaminated with the toxin at levels ranging from 0.2 to 7.3microg kg(-1)". I think this answers the question with a yes, though they are low enough that they will not affect a healthy person. – Chad Dec 28 '11 at 14:19
  • @Chad the sentence right before the quote provided by the OP reads: "Mycotoxins are in almost all low quality brands of coffee." Which is doubly busted: a third does not qualify as "almost all", and the levels make it insignificant anyways. I take "prevalent" to mean "present in enough quantity to give you effects in a significant proportion of coffee". – Sklivvz Dec 29 '11 at 00:34
  • @Sklivvz - Then perhaps the question should be reworded to say present. but the definition I would use is: widespread; of wide extent or occurrence; in general use or acceptance. 30% is indicates wide spread unless 30% was localized to for instance South American or Brazilian coffees. The efficacy is important but not offsetting. – Chad Dec 29 '11 at 14:20
  • @Chad well, the linked claim is quite clear on the matter: there are enough toxins to have an effect, which is *false*. – Sklivvz Dec 29 '11 at 15:26