In the first part of this series I tackled the issue of what to call one of two very different tea processing steps both referred to as “fermentation.” Â In this installment, I’ll discuss what you might call real fermentation.
One type of Chinese tea, called hÄ“i chÃ¡ (literally â€œblack teaâ€ but usually translated as â€œdark teaâ€ to avoid confusion) is often described, confusingly, as â€œpost-fermentedâ€. This, again, is a literal translation from the Chinese term hÃ²u fÄxiÃ o and doesnâ€™t make a lick of sense in English. I donâ€™t know much about the history of this term, but this type of tea is actually fermented, so if youâ€™re calling enzymatic browning â€œfermentationâ€, then I guess you have to call actual fermentation something different? But Iâ€™m getting ahead of myselfâ€¦
Whatâ€™s going on:
Although there are several kinds of hÄ“i chÃ¡, the most popular by far is shu puer tea (also seenâ€”and heardâ€”as â€œshouâ€ puer). To make this tea, you start by making what is essentially a green tea, and that involves using heat to stop enzymatic browning by inactivating polyphenol oxidase. This dry, loose-leaf green tea is then piled in thick heaps on a factory floor, moistened with water, and covered with a tarp made of natural or synthetic materials. The tea may or may not be purposefully inoculated with microbes either from some bits of the previous batch of tea (a starter culture) or with specific isolated strains of microbes. If it isnâ€™t purposefully inoculated, the microbes involved come from the tea leaves, workers hands, the tarp, the factory floor, or the air (microbes are everywhere!). The microbes doing the work here are mostly fungi, especially Aspergillus niger, a fungus which is also used in the production of soy sauce, and Blastobotrys adeninivorans, but many bacteria are present as well.
This pile of tea quickly heats up from the metabolic activity of the microbes that are multiplying and eating and breaking down compounds in the tea. This heat is importantâ€”only very heat tolerant microbes can survive this process, and those happen to be the microbes you want for safety and flavor reasons. It’s also important to keep the pile oxygenated which is done by turning the leaves occasionallyâ€”again, this selects for â€œgoodâ€ microbes over â€œbadâ€ ones. Turning and selectively removing the tarp also keeps the pile from getting too hot and killing everything. Â During this process, the microbes are not only breaking down compounds in the tea, but they are also producing compounds that otherwise wouldnâ€™t be found in tea. For example, shu puer is often found to contain cholesterol-lowering statins produced by microbes.
After 30 or 40 days, the microbial process is slowed by removing the tarp and piling the tea into furrows to help it cool and dry. The finished product is drastically different from the starting material in appearance, flavor, and aroma.
What to call it:
There is substantial debate over what to call the tea itself in Englishâ€”the “shu” in shu puer can be translated either as â€œcookedâ€ or â€œripeâ€. Â As of late, my strategy is to avoid translating at all and just use the Chinese terms, but after deciding on what to call the process that creates this tea, we might just have some good solid reasoning for choosing one translation over the other.
Compared to the process I discussed in part one, this one is much more clearly deserving of the term â€œfermentationâ€ because it actually involves microbes. â€œPost-fermentationâ€, the literal translation of what this process is often called in Chinese, doesnâ€™t make any sense unless youâ€™re going to call some earlier step â€œfermentationâ€ or if this was something that happened after fermentation. I would personally suggest that “post-fermentation” has no place in any realm of tea discussion and should be totally phased out. Â
So is it that easy? Can we all agree on â€œfermentationâ€? Well, thatâ€™s what I thought until I asked a microbiologist. Ben Wolfe is a microbiologist at Tufts University, and he provided a surprising and insightful comment after learning about shu puer and the microbial players involved in making it. Â He asked, â€œIs this actually fermentation?â€
Just like the term â€œoxidationâ€ in chemistry, â€œfermentationâ€ has a slightly different meaning in microbiology compared to everyday English. Fermentation isnâ€™t just any process that microbes carry outâ€”it specifically describes the way microbes get energy from their food when no oxygen is around. Fermenting microbes typically make lactic acid or ethanol as waste products of fermentation. As Professor Wolfe scanned a list of microbes found in shu puer, he noted that none of the most abundant species were typical fermenters.
So what do microbiologists call a food that is made by microbes but not by true fermenting microbes? Ripened foods. Salami, brie cheese, and katsuobushi (AKA bonito flakes) are all examples of microbially ripened foods where exposure to oxygen is necessary in production.Â¹Â On the other hand, kimchi, sauerkraut, and kombucha are all fermented under limited oxygen exposure. Making shu puer is more like making salami than like making sauerkraut because of the importance of oxygen. Too much exposure to oxygen can ruin a batch of sauerkraut but too little oxygen will ruin a batch of shu puer.
If we want to be really specific and geeky, we can call this process microbial ripening which naturally lends support to calling shu puer â€œripeâ€ or â€œripenedâ€ puer in English.
Language is crazy complicated, especially so when youâ€™re dealing with two very different languages, industry jargon, AND scientific jargon. I mostly intend this series as a fun, ultra-geeky delve into a few aspects of tea and not as a suggestion for how everyone in the tea world should talk or write. Honestly, introducing yet another set of terms to the tea world probably isnâ€™t worth the confusion even if the terms themselves are less confusing.
My advice is to approach tea terminology with a goal of clear and friendly communication. As long as there is mutual understanding, thereâ€™s no need for correction or clarification. There are a few situations where I think clarity is especially important and confusing terms should be avoided. For example, when introducing beginners to the world of tea, â€œfermentationâ€ is a really confusing term for what is actually â€œoxidationâ€ or â€œenzymatic browningâ€â€”Iâ€™d avoid that term entirely unless you’re talking about real microbial fermentation or ripening. If youâ€™re writing a scientific publication about tea that a microbiologist or a chemist might read, be clear about whether you mean microbial ripening, fermentation, or enzymatic browning (which all get called â€œfermentationâ€ regularly). Â
On the other hand, if a tea farmer from China is telling you about how they do the â€œfermentationâ€ process for their oolong, suppress the desire to interject with â€œActuallyâ€¦â€ and start taking notes instead!
Â¹As a side-note, the reactions that ripening or fermenting microbes use to get energy from their food would be characterized as oxidationÂ reactions 😉
23 thoughts on “The science and nomenclature of tea processing. Part 2: Microbial ripening.”
Nicely said, well thought out and conveyed.
If pu’er maocha (i.e. loose raw pu’er) is essentially green tea, then what’s the difference between that and Yunnanese green tea and why do they taste so different?
“Post-fermentation” is called that because the fermentation occurs after the leaves are otherwise processed (made into maocha) already, as opposed to during withering, for example. Of course, if one is not to use “fermentation” for oxidized teas, the “post” bit is quite redundant.
Selderijâ€”I’ve actually never had a green tea from Yunnan, so I’m not sure what the difference is, but it could be any number of things. My first guess would be plucking standard since typical green teas are made with younger leaves than puer maocha.
I’m still not totally following the logic behind the term “post-fermentation”. What you said would make some sense if the maocha was a “fermented” tea (really, oxidized or enzymatically browned), but it’s notâ€”it’s a green tea that goes through a “kill green” step and no oxidation step.
Rather like Selderij I tend to refer to such teas as “Post Fermented” in an attempt to describe that it is a process that takes place after the initial processing of leaves has been completed.
To continue on the point of Yunnanese green tea and maocha, a very important difference in the processing is that pu’er doesn’t go through a full killgreen firing: it’s done at a lower temperature, at least to allow some oxidation, and *maybe* also to not kill the microbial colonies already residing in the leaves.
Raw pu’er, even when young, really doesn’t taste that much like green tea, not even Yunnanese green tea. The latter does have its own characteristic compared to other green teas, but it’s hard to mistake it as pu’er. That’s why I think it’s an oversimplification to say that maocha or raw pu’er is essentially green tea. I don’t know what would happen if one was to wet-pile actual green tea, though.
Geoffâ€”I think that’s rather confusing since initial processing never involves fermentation. I could understand “post-processing fermentation”, but I think that would be redundant since it is the only time fermentation happens in tea processing. The other fermented tea, kombucha, is fermented after being brewed and in my experience, tea novices are often confused about the difference between kombucha and puer. Maybe “pre-fermented” is a better term for shu puer 😉
Selderijâ€”I’m not arguing that raw puer isn’t different than other green teas, just that in the Chinese categorization system, it falls definitively in the category of green tea. (see https://www.worldoftea.org/nuances-of-tea-classification/)
A 2015 paper in Food Analytical Methods, for example, shows that raw puer is pretty different from green teas from Zhejiang, Sichuan, Anhui, Henan, Hubei, and Jiangsu provinces based on their chemistry (which is pretty silly because as you stated, you can just taste the difference) (https://link.springer.com/article/10.1007/s12161-014-9900-0)
So WHY is it different than other green teas? Sure, it could be the kill green temperature, but I’m skeptical of that. If that was the major difference, then wouldn’t raw puer just taste more like wulong or white tea? I AM super curious about these Yunnan green teas though, I’ll have to seek some out.
A very good post (as opposed to post-fermented.) Informative, thoughtful and logically argued. Congratulations.
Excellent blog Eric. Here are a few comments to address some of the comments. Thanks for your work!
Puer and the lore about it are by in large a 21st-century tea. When I first traveled to Yunnan in the late 1990s, the majority of the tea produced then was green tea, followed by jasmine and black teas. It was hard to find puer tea in Kunming in those days. It is true that at least since the Qing Dynasty, green tea was pressed into cakes to be exported via small horses to Tibet. It is hard to get good history beyond the Qing because before them Yunnan was not part of China. The Dali Kingdom which ruled Yunnan for more than a thousand years collapsed during the Ming Dynasty.
Not a great deal of tea moved into Tibet from Yunnan; it’s a hard way to go compared to Sichuan where the majority of Tibet tea originated. That the is also green tea pressed into bricks as is most other he cha.
It’s a good idea to read Jiang Jinghong’s book, ‘Puer: Ancient Roads to Modern Chic. A native of Yunnan’did her research for her doctorate in anthropology in the village of Yiwu were the hype began over puer. For the locals making the tea at the time, it was shocking for them to learn it was valuable. They thought of it as green tea that they would throw out after a couple of years. The ideas about there being some scientific truth that Yunnan had special microbes unique to that area that reacted with the tea as it aged had no scientific basis. There has been recent research that indicates otherwise. That the frying (killing the green) tries to maintain the microbes is just part of the hype.
Sorry, I am talking about sheng puer here, not the cooked tea.
Thanks for your comments, Austin! “Puer Tea: Ancient Caravans and Urban Chic” is indeed a great book. I think there’s definitely some hype behind our thinking of puer maocha as something very different and uncategorizable, but it’s also true that it tastes very different than your average green tea. That difference in taste might make it more suitable for aging, but you could certainly age any green tea. A few months back on the Gong Fu Cha Facebook group someone posted a very controversial picture of aged dragonwell which was dark brown in color. Who knows if it was real or not, but it’s not surprising that something green left in a humid environment for a decade would turn brown, regardless of how hot it was cooked.
Excellent article Eric.
Two Japanese dark teas, Awa bancha and goishicha both involve lactic acid bacteria and thus would ironically be more of a fermented tea (in microbiology) than shu and sheng.
Goishicha has a two step process, one with oxygen and one without. That means that it is definitely a post-fermented tea.
Ricardoâ€”Lactic acid bacteria fermented tea!? Oh man, I can’t wait to tell my friend who studies sauerkraut microbes about this! Have you written about the fermentation process for these teas before?
Thanks for these articles! I’ve been endeavouring to use these terms when explaining things to new tea people, and it seems to make much more sense to them compared to using a word like ‘ferment’.
One minor thing: In the opening paragraph you have written å‘é…µ as “fÄxiÃ o” but in part 1 it was written as “fÄjiÃ o”. It looks like “fÄxiÃ o” might be Taiwanese pronunciation but I wasn’t sure if it was a typo, since that sentence was referencing part 1.
I have a lot of respect for your writing, but fermentation is the correct term for the first stage of puerh maturation. In the first stage, the plant material is converted into acids by fungi and some bacteria. These acids become food for the next group of fungi. Was it you or someone else who presented on gallic acid once? That is one of the first stage products. If you want to call the second stage “ripening” or ” maturation,” fine. Otherwise, we have yet another article that just adds confusion to a very simple process.
Cywn, I have no doubt there is some microbial succession happening during wet piling, but the conditions that really emphasize fermentationâ€”the incomplete breakdown of sugars into organic acids or ethanolâ€”is only really promoted under a lack of oxygen. The microbes found in ripe puer are not your typical fermentors (e.g. lactic acid bacteria). No doubt there are some fermenters in there, but they’re not the most abundant microbes, at least at the end of the process. Also, I definitely call the whole thing “fermentation” unless I’m talking to microbiologists who might know and care about the difference!
Hi Eric, I really enjoyed reading this. I had a discussion when my Taiwanese tea teacher called the whole thing fermentation, but now I can put this into the right context. Thanks for being so thorough and analytical. It helps that your article is well-written too.
Thanks so much for the kind words, Sven. Please spread the word! It seems like it’s not widely known in China and Taiwan that “fermentation” in English *only* applies to microbial fermentation.
So can the word aeration take the place of fermentation?
“Aeration” just means adding air (like when you whip egg whites, or turn over compost), and doesn’t say anything about the resulting processes, IMO. I don’t think it makes sense to use “aeration” here.