As we all know, most teas go bad after a while. Not in that they spoil and can't be consumed, but in that they lose freshness and aren't quite as enjoyable as when new. Of course, some teas like sheng puer and certain aged oolongs actually get better with age, but for the most part this holds true. Still, it is my understanding that there is some variation in just how quickly certain teas go bad. My current understanding is very limited and possibly incorrect: Most herbal teas keep rather poorly. Green and white teas also lose freshness fast. Black teas and oolongs keep well, but not tieguanyin, and some oolongs and puers keep indefinitely, often getting even better with age if stored correctly. This is obviously very generalized, but that's my understanding.
Would anyone care to explain longevity in different teas, why certain teas keep better than others, and what I can look for in determining how well a tea will keep?