Pu Er is alive! Inside it, bacterias do a long fermentation job which will change the taste of tea. When the tea is very new, it has very green characteristics. The taste of the mountain is emphasized, it is raw and somewhat wild.
Weeks, months, years will make the tea smoother in the taste and more pungent in the feeling.
Consider young Pu Er as a young man. Its origin gives him a certain taste. As he grow older, the man will experience different things. Pu Er will be exposed to different smells (basically the smell of the ambient air). The temperature and the humidity are the main factor which influence the development of tea. Basically, in a hot and humid climate, the tea will change faster. This does not mean the change will give a good taste. If the air is too wet, the tea could develop mold and taste like it.
Hence it is important to care about the storage place. There are many divergent opinion about how to store Pu Er tea. The safest way to store it is to keep it away from strong smells, to allow a good air flow and to keep the tea from direct sunlight since it could make the tea dry quickly.
It is interesting to notice that in dry storage , the weigh of a cake decreases with time while it increases in wet environment.
There is few you can do about the air quality, unless you accept to move your house to age Pu Er better. Only one important thing: do not spray water on the Pu Er cakes in order to accelerate the fermentation process. It would be the best way to destroy your tea. Let the time to its office...
What does this change consist in?
-the leaves get darker and reddish.
-the greenish aroma of fresh tea disappear.
-new aromas come into the tea, strongly depending on the storage conditions
-the tea soup changes from green\yellow to orange\red
-the tea get more long-running as it ages
-the bitterness gets milder with age
-the astringency often increase in the first years and gets milder in the end
Shu Cha is artificially fermentated to a certain extent. The possibility of evolution for a Shu Cha heavely depends on this initial degree of fermentation. The change is very noticeable in the first years but don't expect much from an old Shu Cha.
As a general rule: Sheng Cha ages better than Shu Cha and old-growth tea evolves more than plantation tea. The price of aged tea follows the same logic, hence it is very common for a ten year old tea to be twenty times more expensive than another one from the same year.