Tokoname Kyusu: The Clay Teapot That Sweetens Tea

Inside the Japanese tea industry, there is a long-held belief. Tokoname kyusu, clay teapots made in Tokoname, Aichi Prefecture, actually make green tea taste better. More specifically, sweeter, rounder, and with more umami. For a long time that claim lived on tradition and the accumulated experience of generations of tea professionals. Then a study put it to the test. More than 2,000 tasters and a taste sensors confirmed it. If you are serious about Japanese green tea, the kyusu you brew it in is not a small detail.

What a Tokoname Kyusu Is

A kyusu (急須) is a Japanese teapot designed for green tea. It usually has a built-in mesh strainer and a side handle. Tokoname-yaki (常滑焼) is one of Japan's six oldest pottery traditions, the Roku Koyo (六古窯) or the Six Ancient Kilns, made in the city of Tokoname in Aichi Prefecture. It is a centuries-old pottery tradition that continues to this day. The local clay used is distinctively high in iron, which gives finished pieces their characteristic dark reddish-brown surface. That iron-rich, mineral-dense clay is what the Japanese tea industry has relied on for generations, and why Tokoname kyusu remains the standard recommendation for brewing sencha and gyokuro.

Before I started our company in the U.S., I trained for and earned a Japanese Tea Adviser certification through the Nihoncha Instructor Association. I grew up in a tea family and assumed I knew most of what I needed to know. I did not. I remember working through the kyusu chapter and finding it genuinely surprising. It wasn’t because the information was obscure, but because I had never thought carefully about the pot itself. I had always focused on the leaf, the water temperature, and the timing. The vessel had seemed like a background thought. The study data in that chapter made clear that it is not background at all. The vessel is an essential part of the brewing equation.

The Study: 2,000+ Tasters and a Taste Sensor

A few years back, an industry group in Tokoname put the traditional claim to a scientific test. They brewed the same green tea in four different teapots — Tokoname clay, porcelain, glass, and aluminum — and ran two evaluations:

• Consumer panel. Over 2,000 tasters drank the four versions and answered a questionnaire.
• Instrumental analysis. The same teas were run through a taste sensor, the kind used in food science to quantify components including umami, sweetness, bitterness, and astringency.

The results were striking. Not a marketing miracle, but a clean, methodical confirmation of something the trade had believed for a long time.

In the consumer panel, more than 75% of tasters reported that the tea brewed in the Tokoname *kyusu* tasted sweeter, more umami-rich, and more delicious overall. Only about 35% described it as bitter or astringent. This was a much lower share than for the other teapots.

The taste sensor matched the panel. Tea brewed in the Tokoname kyusu showed higher umami extraction than the other vessels. Sweetness was also higher. The most interesting finding was the balance between sweetness and astringency. In Tokoname clay, sweetness scored higher than astringency. In glass and aluminum, astringency was higher than sweetness. Same tea, same water, same brewing. The only difference was the teapot.

Why the Pot Matters

Brewed green tea is a chemistry experiment in a cup. You are pulling out amino acids, including L-theanine. These all contribute to umami. There are also catechins, which give bitterness and astringency. Anything that affects the temperature of the water, the way it contacts the leaf, and the balance of the extraction will shift the results of your experiment. The study showed that changing only the pot and using the same amount of leaf, water, and the same same steep time, was enough to move the ratio of sweetness to astringency across a measurable threshold. That is not a small variable. That is the pot doing its work.

Tokoname clay does two things. The mineral-rich, slightly porous clay seems to soften the water and allow a fuller extraction. The body of the pot holds heat steadily, so the water temperature inside the pot stays in the right range for sencha — usually 158–176°F (70–80°C). That steady temperature matters because green tea extraction is sensitive to fluctuations. Water that is too hot means that catechins flood out, bringing bitterness forward. Water that is too cool won’t allow amino acids to escape into the brew. A clay body buffers against both. Glass and metal conduct heat outward more quickly, which means the temperature inside the pot can drift during the steep. The cup tends to taste thinner and sharper as a result. The study's taste sensor was measuring exactly this effect, vessel by vessel.

There is also a longer arc to it. A clay kyusu that is used regularly and cared for properly, rinsed with hot water and never touching soap develops a patina over years. The pores of the clay absorb trace amounts of tea with each brew, and the pot gradually becomes seasoned to the teas you make most. It becomes a personal companion in a way that glass or stainless cannot.

If you are serious when brewing Japanese green tea, this is the upgrade I recommend before any other piece of gear. We carry Tokoname kyusu in our teaware collection for exactly this reason. Use it once with the same sencha you have been brewing in a glass or stainless pot, and the difference is immediate. The cup is rounder, the sweetness is forward, and the bitterness recedes. That is the kyusu doing its job.

— Kyohei Sugimoto
Owner, Sugimoto Tea Company (USA)
Three generations from Shizuoka, Japan

Frequently Asked Questions

Q1: What is a Tokoname kyusu?
A1: A Tokoname kyusu is a small Japanese teapot for green tea, made in the city of Tokoname in Aichi Prefecture using local mineral-rich clay. Tokoname-yaki is one of Japan's six oldest pottery traditions. Inside the Japanese tea trade, Tokoname kyusu are the standard recommendation for brewing sencha and gyokuro.

Q2: Does a Tokoname kyusu really make tea taste better?
A2: Yes — and it has been measured. In a study comparing Tokoname clay, porcelain, glass, and aluminum teapots, more than 75% of over 2,000 consumer tasters reported that tea brewed in the Tokoname kyusu tasted sweeter, more umami-rich, and more delicious overall, while only about 35% described it as bitter or astringent. A taste sensor produced matching results.

Q3: How does a clay teapot change the flavor of green tea?
A3: Two main mechanisms are at play. First, the mineral-rich, slightly porous clay appears to soften the water and pull more umami and sweetness out of the leaf. Second, clay holds heat steadily, keeping the brewing water in the ideal range for Japanese green tea. Glass and metal lose heat differently and tend to produce a sharper, more astringent cup.

Q4: What is the right water temperature for sencha in a kyusu?
A4: For most sencha, brew between about 158°F and 176°F (70–80°C). Higher temperatures pull more catechins and produce more bitterness and astringency; lower temperatures favor amino acids like L-theanine, giving you more sweetness and umami. A clay kyusu helps hold the temperature steady through the steep.

Q5: How do you care for a Tokoname kyusu?
A5: Rinse the kyusu with hot water after each use and let it air dry. Do not use soap — the clay is slightly porous and can hold odors. Avoid sudden temperature shocks (do not pour boiling water into a cold pot from the freezer). Treated this way, a Tokoname kyusu lasts for decades and develops a beautiful patina with use.