Shape and composition of teaware

All of these factors will effect taste, at least some of the time. Porcelain and glass have the least effect on taste, they are fairly neutral. Yixing will absorb the flavors of each tea session and after enough sessions will begin to add flavor to the tea. I have several silver teapots and they will produce a slightly different tasting tea than any other type. I am not sure how cast iron and stainless steel effect taste but teapots are made out of both, generally larger pots. As far as shape goes I don’t think it is a big deal as long as there is room for the tea leaves to expand. Also different kinds of materials hold heat differently, this also effects taste. I think porcelain, yixing, and metal hold heat better than glass but I am not sure about porcelain.

There is no simple answer to your question. For starters I would say that you make a mistake when you mix “tea experience” with “taste”. I would argue these are two different – if overlapping – things.

When it comes to “tea experience”: yes shape affects it since the “experience” is entirely subjective (while taste is not) and therefore everything attached to the tea will affect your experience. Including but not limited to the time of day, your psychological state, if you need to pee and which pot you are using.

As for taste, well, that’s were things gets complicated.
There are many, many opinions, assertions, hypothesis and claims regarding the type, shape and material of brewing vessels and the effect they have (or don’t have) on the taste of the tea. There is very little (if any) evidence for all these opinions and claims, beyond anecdotes and feelings.

It would seem obvious that some brewing vessels retains heat better than others and heat retention is probably a factor that affects tea taste. Note the “probably” because I am not aware of any actual evidence of that but it does seem highly plausible.

As for shape there are claims that some pot shapes are better for some specific teas, like “flat pots for this type and high pots for that type”. These claims seem to originate with Chinese tradition, as far as I can tell, though some rationalize them as having to do with the tea leaves having enough space to expand. While it makes sense that it’s a factor if the leaves can expand freely, I think most of the claims that matches pot-shapes to specific teas are questionable at the very least.
A footnote: one thing that does make a pot less suitable for some teas is how fast it pours. For teas with very short steep times, it’s a problem if it takes a long time to empty the pot (i.e. sheng pu’erh).

Then we have the hypothesis that undressed clay absorbs some of the tea being cooked in it which in turn flavors the contents. This is plausible but there seem to be an automatic assumption that this “flavoring” from the pot will make the tea better and I have no idea why people makes that assumption. Different? Perhaps, but better? Why would it not just as soon make it worse?

Then we have the effects that different types of clay is supposed to have on different teas… this is a can of worms. Suffice to say that there is no evidence I have ever seen for the clay fetishism that is endemic in tea-nerd circles. Especially from people who sell teapots, have blogged for years about the importance of expensive pots and/or have spent a fortune on vintage pots made from certain clay types.

Having said all that, some practical things that are beyond dispute would be:
- You get the tea out of a gaiwan faster than out of a pot and that makes it easier to control the exact steep time.
- Clay is a porous material, glass and porcelain are not.
- Things that retain heat better are hotter for longer.
- Nice pots are nice. Owning and using one will give you a warm fussy feeling all over.

I would love to see some proper blind testing done, with large enough sample sizes and by people who does not have a bias, but that is unlikely to happen so you are left to try to make sense of this on your own.

Thank for your ideas and thoughtful response.

Teas with very small particles might be difficult to prepare in a gaiwan; a kyusu is more appropriate for teas like young senchas with small leaves as it has screen or holes to let through some particulate matter but heeps the small leaves out.

Again, using young senchas as the example, you want a material that will retain the lower temperature at which these teas are brewed, so a glass container that doesn’t insulate well won’t perform as well as a clay or ceramic vessel that will.