Controlling microbes in your Pu-erh cave.

[SlowOx]

I have been troubled since 2013. I've always believed that pu-erh could be aged with storage. After some research--I am learning that this only half the truth (to be generous). In reality, microbes are more important than the environment. Environment will support microbes, but I'd like to take this topic more into the science of aging Pu-erh. Who's in?

[bonescwa]

I would doubt that anyone actually knows which species are common on the tea or even which species of bacteria and fungi are necessary for the process to occur. If anything, the people who make shu might have some knowledge about this. I also don't think there is much known on the chemical process of the microbial fermentation of tea or the balance between oxidation vs fermentation during the process. But I've also been curious about this topic for a while.

[SlowOx]

For starters, I've researched that several microorganism Aspergillus spp. is regarded as the most dominant species in the microbial fermentation of pu-erh.

Also-

"The natural fermentation process normally takes a few weeks. In order to shorten the fermentation time, the dominant species of microorganisms are now extraneously inoculated in the modern processing technology (Chen, Chan, Chang, Liu, & Chen, 2009; Chen, Liu, & Chang, 2010; Hou, Jeng, & Chen, 2010; Liang et al., 2009). Research has revealed that artificial fungus- inoculated solid-state formation could give the main, specific and ex- cellent sensory characteristics of Pu-erh tea, including the infusion colour, taste and aroma, which are comparable with spontaneous fermentation that produces the Pu-erh tea aged naturally for a long time (Chen, Zhang, Zhu, Yang, & Zhang, 2008; Liang et al., 2009)."

[bonescwa]

That's for shu. They do all the microbial control for you.

[Drax]

Do they say which "dominant species" they use in that process? Also Aspergillus?

[solananl]

Yeah, but there are like 200 types of Aspergillus. Hster made an overview of some "puerh mold species" and gingkobay also wrote down "a (relatively) complete list of fungi in puerh" which could be interesting to read.

Aspergillus oryzae (Koji in Japan, used for sake amongst others) can be bought. You could experiment with inoculating a piece of puerh and see what happens.

[SlowOx]

Do they say which "dominant species" they use in that process? Also Aspergillus?

I'll read a little more over this paper I found, but so far no mention of a specific Aspergillus.

Hster made an overview of some "puerh mold species" and gingkobay also wrote down "a (relatively) complete list of fungi in puerh" which could be interesting to read.

Thanks for the info! The trail continues!

You could experiment with inoculating a piece of puerh and see what happens.

I plan to capture as much bacteria off of sheng pu-erh teas as I can and culture them in petri dishes. I hope to inoculate various pu-erh cakes and age them for a month in separate vessels under high humidity.

I've always discussed ageing pu-erh with several tea-shop owners. I'm not convinced that the ageing process really continues beyond the sale date from the manufacturer's point of origin. Everything ends up thinking I have no idea what I'm talking about. Does anyone know of any tea-houses who employ the science of ageing behind the pu-erh they store? I'm shocked that no one seems to do this.

[bonescwa]

I feel like the people who live in humid Asian conditions just know the environmental setting where the aging they want takes place. There are variations (dry vs wet stored) but if they want natural, slow, unenhanced aging then there is no real reason to care about the science behind it, from a practical point of view.

[entropyembrace]

Some problems...

You're quoting papers which are about the fermentation process that is used to make shu puerh. This is different from the slower aging of sheng with much more oxygen availability. There is a lot less information on the microbes involved in the aging of sheng probably for the reasons bonescwa said but also because it's a process that takes many years it is more difficult and expensive to study.

Also trying to grow bacteria from puerh in petri dishes then transfer it to young cakes sounds like a really bad idea. A petri dish is a very different environment from a puerh cake. Water and nutrients are abundant in the petri dish and extremely scarce in a pu-erh cake. While there are nutrients from the leaves because they're dried products the availability is very low. Most bacteria are not culturable in a lab setting at all. Even less are culturable in standard petri dishes with yeast extract nutrient agar. What you're going to do is enrich bacteria which grow well in petri dishes which will be a very different population of bacteria from what are growing on the puerh cakes and then seed that on to your puerh.

If you really want to know what the microbes are on puerh you need to do quantitative PCR to identify the organisms and proportion of each in the puerh cake that you're testing. The reason why a lot of these environmental microbiology studies are not specific down to the species level is that to get that level of detail for a complex microbial community will require a lot of PCR runs with many different primers. That's probably too expensive and technically challenging for amateur science...but it's not an impossible project.

BUT! if you just want to seed microbes from well aged cakes to your fresh young sheng there is something simple you could try. Place the old cakes in contact with the young cakes in your storage

[Drax]

Yeah, I agree with ee on all of those points, with particular caution on the culturing side of things....

I have not seen a good description of what chemical transformations happen through microbe action and what chemical transformation happens through oxidation (exposure to oxygen in the atmosphere). The transformations are likely different, and it's likely one of the main differences when comparing sheng aged naturally to sheng composted into shou.

[entropyembrace]

Yeah, I agree with ee on all of those points, with particular caution on the culturing side of things....

I have not seen a good description of what chemical transformations happen through microbe action and what chemical transformation happens through oxidation (exposure to oxygen in the atmosphere). The transformations are likely different, and it's likely one of the main differences when comparing sheng aged naturally to sheng composted into shou.

The difference in oxygen levels won't just change the abiotic chemistry either. The reactions being performed by the microbes will be different and different species of bacteria will be dominant.

And yes just growing bacteria in petri dishes without knowing what you're doing can be dangerous. Bacteria that grow on nutrient agar petri dishes are often bacteria that grow well on humans. And while not likely to be pathogenic if you get a really high dose exposure to a sensitive area like your eye or a cut it could still cause an infection.

[SlowOx]

There are variations (dry vs wet stored) but if they want natural, slow, unenhanced aging then there is no real reason to care about the science behind it, from a practical point of view.

The science behind it is very important. Especially in my own cave, I want to be able to mitigate contaminant microbes and support beneficial microbes. I also want to be able to continue the aging process.

BUT! if you just want to seed microbes from well aged cakes to your fresh young sheng there is something simple you could try

What makes a well aged cake?

[SlowOx]

Here are some things I've found in my journey to understanding pu-erh:

"dark tea (post-fermented by microbe). Unlike green tea, oolong tea or black tea, dark tea is a unique microbial fermented tea, and its production is only limited to the areas of China and Japan."

"In China, dark tea is traditionally further divided into:
Yunnan Pu-erh tea
Hunan Fu-zhuan tea
Hubei Qing-zhuan tea
Sichuan Bian-xiao tea
Guangxi Liu-bao tea
according to the different producing areas and the processing technologies employed."

I've never experienced anything but pu-erh. Anyone have anything to saw about my findings?

On another note, I"m beginning to learn a little more about the science in ageing pu-erh. I'm starting to wonder if the differences between ripened pu-erh and raw pu-erh are simple one of control and spontaneity:

"Ripened pu-erh uses stains to specifically break down chemical constituent in the tea leaf.

Raw pu-erh, on the other hand is allowed to spontaneously acquire microbes that allow for chemical constituents to break down over time."

This makes sense since these dark teas are geographical product, hence, indigenous microbes are particular to specific areas.

Any thoughts?

[debunix]

This discussion brings to mind lots of scattered bits from reading about cheese and cheese caves and cheese affineurs (experts in storing/aging cheeses), as well as sourdough bread cultures: specific locales may harbor combinations of microbes (and in sourdough, there is a very specific combination desired of fungus and bacteria), some of which are very conducive to the technique and some not so much; depending on how the starter cultures are inoculated and maintained, the special imported starter may thrive, or the local flora may quickly overwhelm over whatever you bring in from outside--for good or ill. But the precise results can be very hard to replicate elsewhere especially if it's you need something more than a single not-too-fastidious pure culture. And while it does have one thing more in common with sourdough than cheese (the end result gets boiled, so at least some of the nastier bacteria are likely to be killed before you drink your experiments), it just seems like a really hard wheel to reinvent from scratch without a lot of time and resources and tea to waste.

[SlowOx]

it just seems like a really hard wheel to reinvent from scratch without a lot of time and resources and tea to waste.

That's a good point. I'm attempting to study individual chemical components of pu-erh at the moment in order to understand the fermentation process. Chemical age occurs with many parts playing a role. I'm going to study these for the course that it takes. It shouldn't take more than half a year or so if I study one a day. After that, I'm going to study the exact components that undergo change.