1/ As of mid-September 2017, there’s a sizeable furor in the Chinese #tea world about charges that pu’ercha is contaminated with a carcinogenic toxin. The pu’er establishment has threatened the accuser, Fang Zhouzi, with a roughly $1M US defamation lawsuit: https://www.gokunming.com/en/blog/item/4014/six_million_yuan_lawsuit_looms_as_blogger_enrages_puer_tea_growers
But, while the above cited article is good as far as it goes, nothing in English so far has really gone into the charges.
2/ If you’re interested in who Fang Shimin (pen name Fang Zhouzi) is, read the gokunming.com article and/or his Wikipedia page: https://en.wikipedia.org/wiki/Fang_Zhouzi
He’s a remarkable guy who’s made a career of annoying powerful people in China. He even has a lively twitter presence (in Chinese) as @fangshimin.
More importantly for present purposes, if you read Chinese, you can find his pu’er contamination charges here: http://www.xys.org/xys/netters/Fang-Zhouzi/kexueshijie/tea.txt
3/ Okay, so what’s Fang complaining about?
He’s warning pu’er drinkers that the fungus, or mold, Aspergillus flavus grows during pu’er processing and storage, and thus they’re likely to be ingesting aflatoxins, the carcinogenic, and sometimes acutely toxic, products of those microbes: https://en.wikipedia.org/wiki/Aflatoxin
4/ If you assume Fang is only talking about shupu, guess again: he is categorical about this being a problem in shengpu as well. He declares that shupu and aged shengpu are the same thing microbially, the only difference being how long they take to arrive at the goal:
This I doubt, and he offers no evidence for the generalization.
5/ I find it interesting that, at this point in history when many pu’er drinkers drink young sheng, he assumes, like an old Hong Kong dim sum parlor habitué, that it’s only the dark stuff that you’d want to drink, and clearly states that the older shengpu gets, the more hazardous it becomes:
6/ The best evidence Fang adduces is from a pair of studies, one in Guangzhou and one in Nanchang, where pu’er was bought in markets and sampled for aflatoxins. 10-12% of samples exceeded Chinese limits for aflatoxin in grains. (These limits are comparable to Westerns standards.)
Unfortunately, there’s no breakdown of the samples by age or sheng/shu. Pu’er is pu’er, right? I’m not sure if this is the fault of the studies or of Fang; he doesn’t give journal citations.
7/ The market sample studies also suffer from testing the leaves, not the beverage.
Fang notes that some pu’er defenders have dismissed the studies on grounds of aflatoxins’ insolubility in water. (People don’t eat tea leaves.) He counters that fermented leaves’ degraded cell structures could easily leak aflatoxins into the broth.
This seems plausible to me, expecially for shu that’s spent months fermenting in a hot pile, but still, why don’t we have measurements for the actual beverage?
8/ Fang mentions that the Pu’er Institute of the Yunnan Agricultural University (!) has found no aflatoxin in the tea it’s studied. He basically laughs this out of the courtroom, asking the reader to imagine what would happen to a researcher at that noble institution who found otherwise.
9/ Fang also mentions a study of an unfortunate patient in Anhui, a habitual pu’er drinker, who came down with acute liver poisoning from aflatoxins. And sure enough, when they tested the pu’er leaves he used, the readings were 6 times the standard for grains (there is no standard for tea.)
But once again, it’s the leaves, not the broth, that was assayed. And there’s nothing on whatever else the victim ingested. Plus, it’s the very emblem of anecdotality.
10/10 So those are the important points, in my opinion. I’ve omitted a lot of fencing with what seem like silly or meretricious opponents.
I think Fang’s case isn’t really strong, but it isn’t so weak that I would dismiss it. I would love to see some sampling of pu’er the beverage for aflatoxins, stratified by age and whether the tea is sheng or shu.