One of the things I haven't been able to find anywhere is where do the microbes in Pu-erh tea come from? I have read that they are added during processing and even heard that they naturally grow on the tea. If that is true why do they occur in pu-erh and not in other teas?
I won't be able to answer the 'microbe' question very precisely. Microbes, by definition, are all around us, but can't be seen. So microbes are there when the plants grow and in the puerh factories. But the question I sense behind is: why is puerh so special that it will evolve over time? And microbes are not the answer to that question. Luckily, Teaparker just talked about it last Sunday at the Taipei Story House.
A. Wild grown puerh
First, to understand puerh, we must see wild puerh trees in their natural habitat in the mountains of Yunnan, at over 1700 meters altitude. Here is a picture of the oldest tree, 1700 years old and over 30 meters high.
Other tea trees are also able to survive in the wild and grow quite old, but puerh beats them in terms of size, longevity and amount of polyphenols. The last point is quite important: puerh tree leaves contain much more polyphenols than other tea leaves. Not only are polyphenols healthy, but they are what gives tea its nice fragrance and mouthfeel.
That's why you can brew them more often and why they have more aging potential. (Other teas need to be stored in airtight jars, puerh can be kept just protected by its paper wrapper.)
Wild puerh trees get their strength from the rich forest soil and their long roots. A diverse and luxuriant flora adds to this strength. For instance, you can see lichens grow on the puerh trees. This foam looking mushroom is an indicator of an environment that is clean and not polluted. Why? Because it accumulates minerals (from the rain) to grow. If heavy metals are present in the rain, then the lichens die.
The leaves get also bitten by insects (a good sign to see if your puerh is naturally grown or not). What doesn't kill it makes it stronger.
There are many different kinds of wild puerh trees in Yunnan. With its 394 000 square km, Yunnan is as big as 3/4 of France. But what these big leaves/small leaves trees have in common is a formidable strength to grow naturally in high altitude. This is what makes their leaves so enduring.
B. Plantation puerh
The big majority of puerh on the market (over 95%) comes from fields like these below:These are man planted and managed tea plantations that use seeds of puerh trees, but planted at lower elevation in fields.
The DNA is the same, but the environment is very different. Puerh trees need a lot of nutrients to produce their polyphenols. In such plantations, it's quite obvious that fertilizer needs to be added. The lower elevation will also reduce the cha qi of such leaves.
You can still find very decent plantation puerh if the fertilizer used is natural and if the process is handled correctly (Using the traditional method of sun drying the leaves, for instance). However, such puerh will never come close to real, well made, wild puerh.
Conclusion: the magic of puerh comes from inside the leaves, which are a product of the environment. It doesn't come from the microbes or a specific process. Loose puerh will age differently, but is as tasty as compressed puerh.
Acknowledgement: The first 2 pictures came from this website. The puerh fields came from Downtheroad. You can also check this page to see more wild puerh trees.