Cooling speed of water differs depending on the volume of teapot | HOJO Online Speciality Tea Shop

The smaller the size of teapot the faster the temperature it cools down

Some people tends to use a small teapot to brew tea, and assumed that smaller teapot can hold the temperature. The fact is the smaller the teapot, the the faster the temperature drops. It is because of the ratio between the inner surface area and the volume of water. The specific surface area becomes smaller when the volume of teapot is bigger. On the contrary, the smaller the teapot, the more specific surface area. As a result, more water exchanges its heat energy with the surface of clay and it cools down water faster. After all, the smaller the teapot, the faster it cools down. Relatively, the big teapot can hold the temperature for a longer time.

Brewing Japanese green tea

In general, the brewing temperature of Japanese green tea is recommended at below 80 degree C. It is because most of Japanese green teas are grown with fertilizer which makes the taste of tea very bitter. The bitterness comes from caffeine. The caffeine will be effectively extracted with hot water above 80 degree C. So, if we brew tea at below 80 degree C, you can avoid or minimize the bitterness.
On the other hand, some Japanese green teas grown without fertilizer originally give the least bitter taste. So, it is not necessary to brew it at lower temperature. On the contrary, it is very important to brew these teas at higher temperature in order to effectively extract the flavor substance, reduce the astringency and enjoy a clean and clear drinking sensation.

A big teapot is suitable for a beginner.

Brewing tea at high temperature is not that easy as how it sounds. It requires various brewing skills, such as pre-heating of teapot and rinsing tea with boiling water. In most of the cases, a beginner might face greater challenges to brew tea at high temperature. Considering this fact, we recommend the beginner to use a bigger teapot. As I mentioned earlier, a big teapot retains the heat for a longer time. Even if one does not have a good skill of brewing, it is less difficult to maintain it at very high temperature throughout the brewing. Of course, a small teapot is also a useful equipment as long as it is handled with skills.
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Measurement of water temperature in different size of teapot

The above video was made based on three different sizes of teapot. These teapots are made from exactly the same clay (i.e., the Akitsu Mumyoi Oxidation Fired Teapot). I poured boiling water into three teapots and left for a minute. The volume is 100ml (right), 140ml (middle) and 300ml (left). We noticed that there was 6 degree C of difference. These teapots are not pre-heated.

100ml 79℃
140ml 83℃
300ml 85℃

The room temperature was at around 25 degree C. If we conduct the same experiment in a colder room, the difference will be more. If the teapot with the volume of 100ml is not pre-heated, the temperature reduced around 20 degree C. The temperature inside the teapot is much lower than what we imagine.

PS: Additional Note

I tried the same experiment when teapots were pre-heated. I used 2 teapots, the smallest one and the biggest one. They were pre-heated for 10 seconds with boiling water once and twice respectively. The temp was measured after 1 minute. With one time pre-heating, the small one was at 81.5 degree C, while the big one was at 89 degree C. With double pre-heating, the small one was at 89 degree C, while the big one was at 91 degree C. It looks like we need an extensive pre-heating when we use a small teapot.