There’s a whole lot of traditional wisdom in tea, and brew vessel selection is certainly subject to plenty of it. In my experience, tradition would dictate a glass or thin porcelain gaiwan for green and often white teas, a gaiwan - either thick or thin - for light oolongs, a thicker gaiwan or teapot for darker oolongs, and a teapot exclusively for black and pu-erh teas.

I was a bit suspicious - does a gaiwan really lose that much more heat than a teapot? Does a thick gaiwan really brew hotter than a thin one? (On this question especially, I was very suspicious given that thick ceramic pour-over brewers are actually a very poor choice, given that they require an absurd amount of hot water rinsing to heat up properly. I highly recommend this reddit post if you’re curious about that topic.)

Anyway, I decided to investigate this with the three brew vessels shown above. From left to right, we have a very thin porcelain gaiwan, a very thick ceramic gaiwan, and a pretty thick unglazed “Yixing” teapot. All are between 120 and 150ml in capacity. If traditional wisdom is right, heat retention should increase from left to right, and if my suspicions are right, then the thick gaiwan should actually retain the least heat.

[here’s the super thin porcelain on the porcelain gaiwan; it’s so thin as to be translucent in the right light; I was drinking a lovely Ali Shan oolong at the time.]

So here’s the procedure:

I heated each vessel with water at 205F for just over a minute, pouring in a few segments as to avoid giving one a head-start. I then measured temps, and at this point the thick gaiwan was noticeably cooler (154F water) vs. the others (169, 170F for the yixing and ceramic). I then poured out the water and poured in more 205F water as if I were brewing a tea. Now the difference lessened dramatically. From left to right, I got 185, 180, 187F respectively. So the thick gaiwan was still the coolest, but by less of a margin. At one minute, the gap lessened once again (177, 174, 179), and at two minutes, all three were virtually identical (173, 173, 174). It’s plausible that the thick gaiwan would be slightly hotter than the other two in the final minute or two of a very long brew.

First of all, the differences between these devices were pretty small in absolute terms. It’s probably best to pick tea brew vessels based on aesthetic and kinesthetic-enjoyment terms rather than pretty arbitrary traditional wisdom. That said, it’s important to preheat, and if you do so, brew vessel selection becomes relatively unimportant. (It causes a 12-25F difference and reduces variations between different types of brew vessels!) Thicker vessels tend maintain cooler temperatures than thinner ones, at least for typical gong fu cha brew times (30 seconds to 2 minutes). (This is for the same reason that thin pour-over brew vessels suffer from less heat loss - less mass to heat up.) Teapots may offer slightly improved heat retention, but only by a small margin.

[yixing detail; it’s pretty thick for a yixing, but most yixings are actually pretty thin - maybe traditional artisans had the right idea, since thinner designs actually tend to retain heat better.]





[quickie excel graph of the data]