Yuzamashi
A wide open bowl with a pouring lip whose only job is to cool water down. It looks like a small serving jug and it is a thermometer substitute: for Japanese green tea you need water at 50 to 70 degrees Celsius, and this is how you get there without a kettle that can be set.
- Capacity
- 150 to 300 ml
- Material
- porcelain or unglazed clay
- Origin
- Japan
- Best for
- getting water to 50 to 70 °C without a thermometer
What it is
The name means water cooler. It is deliberately wide and shallow rather than tall, because surface area is what sheds heat, and it is usually unglazed or thin ceramic so the vessel itself absorbs some heat on contact. Capacity is matched to the pot it serves, typically 150 to 300 ml.
What it does to your tea
It sets the temperature, and it does so by two mechanisms at once. The first is contact: a cold vessel takes heat out of water immediately, and how much depends on its mass. The rule of thumb in Japanese practice is that each transfer into an unheated ceramic vessel drops the water about 10 degrees, and that is corroborated from an unexpected direction. Francl measured Western teapots and found a cold 400 g glass pot took boiling water down about 10 degrees on contact, while a 1200 g cast iron pot took it down about 20. So the rule is real and it is mass-dependent rather than a constant: a light vessel takes about ten, a heavy one takes more, a pre-warmed one takes almost nothing. The second mechanism is time, since the wide mouth keeps shedding heat while the water sits.
What it suits
Any tea brewed below boiling, which in practice means Japanese greens, and gyokuro above all.
How to use one
Pour boiling water into it and wait, or chain transfers: kettle to yuzamashi to pot gets you roughly 20 degrees down, kettle to cups to yuzamashi to pot gets you to around 65. For gyokuro at 50 to 60 you will want both transfers and a wait. Warm vessels take less heat out than cold ones, so a second round of brewing needs a longer wait than the first.
How to choose one
Wide and shallow beats tall and narrow, because the whole point is surface area. Unglazed absorbs a little more heat on the first pour. Match capacity to your pot, since cooling more water than you need just means pouring the rest away.
Care and cleaning
Rinse and dry. If it is unglazed, no detergent.
What people get wrong
Treating the 10 degrees as a fixed number. It depends on how heavy the vessel is, whether it is already warm, and how long the water sits, and by the third round of infusions your whole set is warm and cooling far less than it did at the start. Taste and adjust rather than counting transfers.
What it is made of
Sources
- a cold 400 g glass pot took boiling water down about 10 °C on contact and a 1200 g cast iron pot took it down about 20 °C Francl, M. (2024). Steeped: The Chemistry of Tea, chapter 7. Royal Society of Chemistry