Yellow tea is a broad class or type of tea, usually considered as a category of its own, alongside green, black, white, oolong, and dark/hei cha (Pu-erh) teas. Of these more well-known types, yellow is most similar to green tea, but it has certain distinctive characteristics of aroma, color, and flavor, and is produced in a distinctive way.
Where is it produced?
With the exception of a peculiar tea produced by Goomtee estate in Darjeeling, India, and possibly a few others, these teas are produced almost exclusively in China, in at least six different provinces, the best-known of which are Anhui, Hunan, and Sichuan provinces.
Yellow teas are often produced exclusively from tips or leaf buds of the Camellia sinensis plant, which are known to be the part of the plant that is highest in caffeine. Tippy varieties include huangya, meaning yellow buds, such as Huoshan huangya, as well as Junshan yinzhen, meaning Junshan silver needle. It would be reasonable to assume that these teas are likely to be quite high in caffeine, possibly considerably higher than typical loose-leaf teas. However, in the absence of clear scientific studies which compare these teas to others, it is not safe to say anything more with certainty.
Because it is so specialized, and because it tends to be consumed by connoisseurs interested more in taste and nuances of aroma and flavor than people seeking health benefits, the health benefits of yellow tea have not been extensively studied or compared to other more common teas. Because it is so similar to green tea, it seems reasonable to assume, in the absence of more information, that yellow teas are likely to be roughly similar to greens in terms of their chemical composition and effects on mind and body.
Production and processing:
The processing of yellow teas is similar to that for green teas, but differs in that there is an additional step, in which the gathered leaves are allowed to sit and yellow somewhat, giving the tea its distinctive character (and name). Most teas processed in this way, like huangya and Junshan yinzhen, are made exclusively from buds or leaf tips.
These teas are thus slightly more oxidized than green teas. Like greens, further oxidation is halted by the heating of the leaf, which is contrasted with white teas which are minimally processed and often will continue to oxidize somewhat in storage.
Buying yellow teas:
If you are looking to purchase yellow teas online (probably the best way for most people to locate this and other types of loose-leaf specialty teas), I would recommend buying from a retailer that is knowledgeable about traditionally processed Chinese teas.