Slightly aged versions, versus “middle aged”: depending on initial aspects, some sheng might be improved — and great — after a year or two of storage and transition; or even three or four. It could make sense to prefer versions aged for longer, but preferences tend to bunch towards liking “young” (not-so-aged) or more fully-transitioned versions; with different people describing the awkward in-between timeframe differently. Really that wouldn’t be standard – it would be a function of the starting point and storage conditions, along with preference.
Fully aged sheng: people dispute what that means, although usually a relatively fixed timeframe gets mentioned along with claims. After 10 years in moderately humid storage, teas can transition a lot; but 15 years is typically closer to fully aged. Even then sheng tends to keep changing, leveling off more in terms of transition beyond 20 or 30 years per my experience (limited for versions that old, and the oldest I’ve tried was still shy of aged for 40 years). Older sheng can kind of resemble shu (an idea that comes up in discussion) but I find it’s not hard at all to tell the difference, so they can be more vaguely comparable than similar.
Testing aging results, comparison tasting: I’ve done lots of this, just not relative to experienced pu’er drinkers: In a sense I’m barely getting started. In the most recent version I compared three tuochas between 4 and 7 years old (kind of in that middle range), and not long ago I compared 2006 and 2007 CNNP / China Tea sheng versions, one of which may well have been a copy of sorts. I’ve not been checking out the higher quality, more rare and sought-after origin versions for the obvious reason – those cost a lot. This 1980 and 1993 versions comparison covers some typical longer aging effects.
There is limited potential to assess results tied back to inputs if you aren’t familiar with the starting point, but an accurate take on that requires tasting the same tea back when it was new. Some teas that are great initially tend to just fade; some that are relatively undrinkable are quite suitable for positive transitions, and others aren’t. It takes an incredible amount of exposure to piece factors and trends together, but for sheng drinkers it’s a labor of love.
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