Hiya.
Depends how long you’re leaving between infusions, but generally I find it best to keep the lid on. (I guess this helps avoid oxidisation of leaves)
During infusion, usually I believe it’s best to keep lid off for green teas, or perhaps put the lid on towards the end of the infusion. (particularly if it’s a long infusion) For oolongs, red, puer best to leave lid on. Also, I hear some people believe gaiwains are not best for green or puer- glassware for green, yixing for puer.
The type of gaiwan is a factor too, but I think leo has gone over this somewhere else… A nice analogy I found for the gaiwan is thinking of its three parts representing heaven, humanity, earth. It’s nice to think of how much this symbolism permeates all levels of tea culture.
