Debunking some fermented-tea misinformation

Edited to change the title from “FUD” to “misinformation” as the former might be interpreted as implying a commercial motivation, which is not my intention

This started as a reply to a thread on fedi, but it got long so I moved it to the blog. The thread describes a blog article in Chinese

I’m judging by this article alone (and in translation), so take this with a grain of salt, but this guy looks like a total crank.

Where to even start. I'll set aside the half of the article that's setting up his bona fides as the aggrieved party or attacking his critics, because I'm neither familiar with the history nor with sinosphere “discourse” to judge what's going on there, except to say: so-and-so's wife even chimed in, and she's just a singer? Assuming there wasn't a massive failure of machine translation going on, this reeks of both credentialism and anti-woman sentiment.

Fermented food production

This is the biggest red flag for me. He asserts that pu'erh production is completely out of control, and that normal fermented foods must be inoculated to control the fungal composition. This is flat out wrong.

Traditional methods of fermentation have been widely studied, from lacto-fermentation, to cheese production, wines, beers, etc. Sometimes the steps performed alone can produce a reliable fermentation with a predictable mix of bacteria and fungi (as in sauerkraut, kimchi, sour pickles, etc). Sometimes, as with spontaneous beers, and most traditional European cheese production, the environment in which the production takes place plays a key role. In these cases, there is inoculation, but it is informal, and happens from the ambient environment. It is not however, less effective for it.

All of this is well studied.


Shu is produced in specific facilities. They are able to turn out a consistently similar product, batch after batch, year after year. This isn't proof of controlled fermentation, but it is highly suggestive. That is what traditional controlled fermentation looks like.

I started seeing studies about the fungal composition of pu'erh tea maybe 20 years ago, and it always seems to contain mostly the same mix: Aspergillus and Penicillium in particular. Here's one random example from about a decade ago.

This is what one would expect from controlled fermentation.


I'm a bit more concerned about sheng, and here he may have a point, to the extent that the post-fermentation is performed at home by non-experts. The warehouses and cellars that produce reliable aging are probably more consistent. Given its age, I'd expect Yee On's cellar for example to inoculate teas with a pretty consistent profile of spores. I believe the studies on shengpu correctly draw their samples from these larger facilities, which is how most sheng is aged. But that probably leaves a larger gap in the data about home-aged teas.

Whither contamination

He just asserts that pu'erh is widely contaminated with carcinogens. From the studies I've seen, this is false. He presumes that this comes from uncontrolled fermentation, and thus doesn't apply to other tea types. The fermentation of pu'erh is certainly well controlled for shu (the results would be disgusting otherwise), and for sheng it really depends on the history of a particular sample.

But what about other teas? This is an interesting study on mycotoxins in various tea styles. The most contaminated tea was a black tea. In particular, the mycotoxin contamination of tea appears to occur in the fields, in the actual growing of the plants. If that is really the primary vector, then no tea style would be spared, and the focus on pu'erh is (almost) completely unwarranted. Almost, because poorly aged shengpu could of course continue to grow the hazardous fungi from the fields. That is a hypothetical, however, and so far the worst offenders seem to be badly produced black tea.