Check out Mike Petro's website, Pu-erh, A Westerner's Quest
if you have a chance. He gives quite a bit of introductory information about Puerh. Unfortunately, to add to the confusion, he calls shu/cooked/ripe by the name black
, which is not a common name for shu in English and he uses the term oxidation
when the correct word is fermentation
Loose tea leaves are wetted, piled up, sometimes under blankets to ferment rapidly before the leaves are pressed into cakes. This fermentation (action of microbes) darkens the leaves and to some extent mimics the taste of old sheng. The process takes several days, even up to a month. Once the fermented leaves are pressed into cakes and dried, they are more or less ready to drink. Letting shu cakes sit for a year or two is sometimes advised to mellow them out.
Raw puerh leaves are pressed into cakes while still green and allowed to dry out. Fermentation occurs in raw puerh also, but only very slowly over the years in the dried and pressed cakes. You can drink sheng when it is very young (most of us here drink quite a lot of the young stuff), but it can be rough sometimes and its real destiny is to be drunk aged ... ten to twenty years down the road.
is the result of microbial action, like yeast converting grape sugars into alcohol or bacteria converting milk into yogurt. Fermentation is a rather slow process, generally occurring over days.
is the process that makes black and oolong tea. It is caused by changes in the green leaves brought about by plant juices (sap) coming into contact with oxygen. It is not caused by microbes. Oxidation
is what happens to a slice of apple when you leave it exposed to air. Oxidation occurs within hours, not days.
for more on oxidation vs fermentation.