A Deep Dive Into Deep Steamed: How Fukamushi Sencha Works, and Why It Was Invented

For about three years there was a glaring gap in the Tealife range. We carry a selection of Japanese green tea I am proud of, and for most of that time there was no fukamushi-sencha in it at all. We used to carry a Shizuoka deep steamed sencha. I thought it was good tea, but the quality moved around from lot to lot in a way I was not comfortable with, so I stopped it and went looking for a better source.

Then I did not look very hard, for a long time. Part of the reason is that deep steamed sencha is genuinely easy to find. Walk into Don Don Donki (Japanese Supermarket) and look at the sencha on the shelf: most of it is fukamushi. Not necessarily good fukamushi, but ticking the box is not difficult, and a box that is easy to tick tends to slide down the list.

Last month I made a trip to Japan, and I found one I actually wanted to carry, which is what set off the reading that became this article. Tealife now sells fukamushi-sencha again, so I have interest in you finding this tea worth drinking haha. The tasting came first and the decision followed it, and what I want to do here is explain what is actually happening inside the leaf well enough that you can judge the tea for yourself.

The part that surprised me most was the history. Fukamushi-sencha exists because a tea region could not sell its tea.

If you are new to this tea, our introduction to Fukamushi-Sencha covers what it is and how to brew it. This article goes underneath that.

The Makinohara plateau in Shizuoka sits across what are now the cities of Kikugawa, Makinohara and Shimada. By the standards of Japanese tea geography it has real advantages: the climate suits the plant, the land is workable at scale, and the region became one of the largest producers in the country.

It also had a defect that no amount of skill in the field could fix. Compared with other producing regions, the area runs hotter and receives more hours of sunlight.¹ Tea plants respond to sunlight by producing catechins, the polyphenol group responsible for most of green tea's astringency and most of its studied health effects. You can read more in our article on the nutrients in Japanese green tea. More sun meant thicker, fleshier leaves carrying more catechin, and more catechin meant a harsher cup.

The consequence was commercial rather than agricultural. Processed by the standard method of the time, tea from this region was classified domestically as 中級茶 (chūkyū-cha), mid-grade tea.¹ It sold, but it sold cheaply, and it was never going to compete with the mountain-grown teas of Honyama or Uji on refinement. A region with excellent land was locked out of the top of its own market by the taste of what it produced.

Around 1952, farmers in 六郷村 (Rokugō-mura), a village now part of Kikugawa City, began experimenting with the manufacturing process itself.¹ The account comes from 『菊川町茶業誌』 (Kikugawa-chō Chagyōshi), a town tea-industry history published in 1984, and it is the source the Japanese government relies on today in its official filing for the region.

Their target was the first step in green tea production, called 蒸熱 (jōnetsu), the steaming that halts oxidation immediately after plucking. It is the step that makes Japanese green tea Japanese: most of the world's green tea is pan-fired, and steaming is close to unique to Japan. The farmers of Rokugō pushed it much longer than the standard practice of the day, and after considerable trial and error found that extended steaming produced a tea with markedly less astringency and a better taste.¹

The timing is worth sitting with, because these men were not working in isolation. Post-war Shizuoka was rebuilding an industry that had lost its export markets, and almost everything about how tea was made was being reconsidered at once. Yabukita, the cultivar that would eventually cover most of the country's tea land, had been designated a Shizuoka recommended variety in 1945 and became a nationally registered cultivar in 1953, one year after the Rokugō experiments began.² Planting stock was being standardised. Rolling and drying machinery was being redesigned and scaled up. The region established Japan's first dedicated tea cooperative, ahead of anywhere else in the country, which meant technique could be shared and quality standardised across many farms rather than staying inside one shed.¹

So deep steaming was not a lone flash of insight. It was one experiment inside a decade when a whole region was rebuilding how it grew, processed, organised and sold tea, and it happened to be the one that changed what Japanese tea tastes like.

Deep steaming is not a loose descriptive term. It has a formal definition.

The 緑茶の表示基準 (Ryokucha no Hyōji Kijun), the Green Tea Labelling Standard maintained by 公益社団法人日本茶業中央会 (the Japan Tea Central Association), sets out the names and definitions of Japanese green tea types. It defines 深蒸し煎茶 as tea manufactured in the same way as sencha, but with a steaming time two times or more that of sencha.³ These definitions are not merely a trade convention. Japan's Consumer Affairs Agency reproduces them in its official guidance on the Food Labelling Standard.⁴

The definition is a ratio rather than a duration, which is why published figures vary. For the underlying numbers, Kagoshima Prefecture's tea industry material gives the working classification used in the trade: shorter than usual is 浅蒸し (asamushi), light steaming; the usual time is 普通蒸し (futsūmushi), normal steaming, given as 30 to 40 seconds; and two to three times the usual is 深蒸し (fukamushi), deep steaming.⁵ In practice this puts most deep steamed sencha somewhere between 60 and 100 seconds, and teas pushed as far as 180 seconds are sometimes sold as 特蒸し (tokumushi), extra-steamed.

There is a practical use for this. Packaged tea sold in Japan must carry a 名称 (meishō) or product name field, and 深蒸し煎茶 is one of the defined names permitted there.³ If you are standing in front of a shelf wondering whether what you are holding is deep steamed, you do not have to judge by the look of the leaf. You can read the label.

The usual short explanation is that long steaming breaks the leaf's cells so the tea extracts more easily. That is true, and it is not the whole mechanism. The Japanese government's technical account of why this tea tastes the way it does names two changes.¹

The first is pectin. Extended steaming raises the content of water-soluble pectin in the leaf.¹ Pectin is the structural carbohydrate in plant cell walls, and it is the same substance sold in packets at Redman or any baking supply shop for setting jam and jelly. Dissolved into the liquor it contributes body and a soft, coating texture, and it suppresses the perception of astringency. This is why a good fukamushi feels thicker on the tongue than an ordinary sencha brewed to the same strength, and it is a different thing from simply extracting more.

The second is a colour change. Under prolonged heat, chlorophyll converts to pheophytin, which is chlorophyll that has lost the magnesium atom at the centre of its molecule. The practical effect is that both the dry leaf and the brewed liquor shift from a green-type colour toward a yellow-type one.¹ Our article on chlorophyll covers the compound itself in more detail.

I find that second point genuinely interesting, because anyone who has drunk this tea knows the cup looks green. The official description of the registered Kikugawa product is 濃厚な黄緑色, a dense yellow-green,⁶ and the pigment chemistry is moving away from green rather than toward it, yet what arrives in front of you reads as green. My own reading, and I want to be clear this is my inference rather than something the research states, is that most of the colour you see is not dissolved pigment at all. It is suspended leaf.

Long steaming leaves the leaf structurally weak. Through the rolling and drying stages that follow, it fragments, and the cell membranes rupture far more readily than in a normally steamed tea.⁷ The finished product carries a high proportion of fine particles, and those particles pass through the teapot filter and into your cup, where they stay in suspension. The result is a cloudy liquor, an appearance the Japan Tea Central Association describes directly as 濁った水色 (nigotta suishoku), cloudy liquor colour.⁷

This is also the mechanism behind the nutritional argument for the tea. Several compounds in the leaf do not dissolve in water and are normally discarded with the spent leaves: beta-carotene, vitamin E, dietary fibre, chlorophyll and various minerals. Because you are swallowing leaf particles rather than only an infusion, you consume them.⁸ ⁹

A soft, fragmenting leaf is a problem for every machine downstream of the steamer. The invention was not finished until the equipment caught up with it.

The Japanese government's filing credits the improvement and enlargement of the 粗揉機 (sojū-ki), the coarse rolling machine that performs the first and roughest kneading stage, as a key reason deep steamed quality improved dramatically.¹ Normal rolling equipment tore deep steamed leaf apart. Larger, gentler machines designed for the material turned an interesting experiment into a product that could be made consistently and at volume.

The control problem is subtler than it looks, and it is worth knowing if you ever read a Japanese producer's description of their process. Deep steaming is not always measured in seconds. The production standard for the registered Kikugawa product recognises two machine types and controls them differently: belt-fed steamers (送帯式蒸機, sōtai-shiki mushiki) are regulated by steaming time, while rotating mesh-drum steamers (網胴回転撹拌式蒸機, amidō kaiten kakuhan-shiki mushiki) are regulated by the tilt angle of the drum and its rotation speed.¹ Leaf tumbles through the drum, and the angle determines how long it takes to fall out the other end. Shizuoka prefectural research gives a sense of the sensitivity involved: in one trial, a drum tilted at 10 degrees held the leaf for around 16 seconds, while 15 degrees cut that to around 12.¹⁰ A few degrees of angle is the difference between one tea and another.

The clearest measure of how new this tea is comes from the 全国茶品評会 (Zenkoku Cha Hinpyōkai), the National Tea Competition, Japan's most important annual judging of tea quality.

In 1969, Kikugawa entered deep steamed tea into the competition for the first time. It had to go into the freestyle division, because no category for it existed.¹ Over the following decade, 363 deep steamed entries were submitted across the competition, and 89 of them, roughly a quarter, came from Kikugawa alone.¹

In 1979 the competition created 深蒸し煎茶 as a formal judging category in its own right.¹ A style of tea that had not existed three decades earlier now had its own division at the national level. The category is only 47 years old.

The dominance continued. According to 『月刊 茶』 (Gekkan Cha), a trade monthly, of 545 deep steamed entries across nine competitions in the 14 years to 1982, 188 came from Kikugawa, more than 30 percent, and 70 of those took prizes.¹ Over that period no other locality came close.

The method itself spread outward from the Makinohara plateau. It reached tea regions outside Shizuoka during the late 1960s and early 1970s, and by the second half of the 1970s it was being produced across the country.¹

In March 2023, 深蒸し菊川茶 was registered as a protected geographical indication.⁶ One point is easy to misread here: the protection covers the Kikugawa name and its production standard, not the deep steaming method. Anyone anywhere may make fukamushi-sencha. Only tea grown and processed to the registered standard in the designated area may be sold as Kikugawa's.

Because deep steaming describes a stage of processing rather than a plant or a growing method, it can be applied to any tea that is steamed at all.

Gyokuro and kabuse-cha are both defined by cultivation rather than processing. Gyokuro is leaf from a garden shaded for around 20 days from the point the first-flush shoots emerge, then manufactured in the same way as sencha; kabuse-cha is shaded for around seven days before plucking.³ Neither definition says anything about how long the leaf is steamed, which means a deep steamed gyokuro is still, properly, gyokuro.

Tealife carries one, so it is worth saying what that name does and does not mean. There is no 深蒸し玉露 among the tea names defined in the labelling standard. The 深蒸し designation exists only in relation to sencha, so "fukamushi gyokuro" sits under the standard's optional labelling provisions, which allow producers to name tea types beyond the defined list.³ It describes what was done to the leaf rather than certifying a category. The tea is genuinely gyokuro and it is genuinely deep steamed. The combination simply has no official name.

Any discussion of this tea eventually reaches Kakegawa, the neighbouring city that has become the most famous deep steamed producer of all, and the health claim attached to it. This deserves to be stated accurately, because it is routinely overstated.

The underlying fact is real. Kakegawa records the lowest cancer mortality rate of any Japanese city with a population above 100,000, based on national vital statistics for 2008 to 2012.⁹ Kakegawa is also a city where deep steamed tea is the dominant local product and where residents drink a great deal of it.

What that fact does not establish is causation. It is an observation about an entire municipality, and municipalities differ in many ways at once, including diet, income, age structure and healthcare access. A city-level correlation is a reason to investigate, not a finding.

The investigation actually happened, and it is the more interesting story. From June 2009, a research programme commissioned by the Ministry of Agriculture, Forestry and Fisheries and known as the 掛川スタディ (Kakegawa Study) brought together Kakegawa Municipal General Hospital, Tohoku University, the National Agriculture and Food Research Organization's tea research division and Kyushu University.¹¹ It combined a cohort study, a controlled intervention trial, analysis of how the physical form of the tea affects absorption, and work on catechin receptor expression.¹¹ Kakegawa City reports the outcomes as reduced LDL cholesterol and reduced waist circumference among participants.⁹

Reduced LDL and a smaller waist is a considerably narrower claim than the one the marketing makes. It is also a far better one, because it came from a trial rather than a map.

Kakegawa's other distinction is less contested. Its deep steamed tea has won the 産地賞 (sanchi-shō), the National Tea Competition's award for the finest producing region, 24 times as of 2022, more than anywhere else in Japan, including ten consecutive years from 2005 to 2014.⁹

Everything above has consequences at the teapot, and they run in a specific direction.

Brew it short. The leaf has already been broken open, so extraction happens quickly, and the timings that suit a normal sencha will overshoot. Around 30 seconds is the working figure, and our guide to brewing fukamushi-sencha covers temperature and ratio in detail. As a starting point, 4g of leaf to 120ml (4 fl oz) of water at 70°C to 90°C (158°F to 194°F) depending on grade.

Expect less aroma, and do not treat that as a flaw in your technique. This is the acknowledged trade-off of the method rather than a fault, and the Japan Tea Central Association states it directly: longer steaming reduces both astringency and aromatic character.⁷ You gain body, sweetness and colour; you give up the high, fresh top notes that a lightly steamed sencha from a mountain garden will give you. Neither is better. They are different teas, and the honest way to sell this one is to say so.

Drink the bottom of the cup. The sediment that settles at the base, called 底だまり (sokodamari), is not a defect. It is the insoluble fraction described above, and leaving it behind means leaving behind most of what makes this tea nutritionally distinct.

Get the filter right, because this is where most people go wrong with a deep steamed tea. Two separate properties matter and they are easy to confuse. How fine the holes are determines what the filter holds back, and you do want them fine, or the sediment simply pours through. How much total filter area there is determines whether it clogs. A small filter with fine holes blocks almost immediately; a large filter with the same fine holes keeps flowing, because the leaf that settles against it never covers all of it.

In practice this rules out the traditional ceramic strainer, the dome of hand-drilled holes formed from the same clay as the pot. Those holes are relatively few and cover a small area, and with deep steamed leaf they clog quickly, particularly from the second infusion onward.¹² What you want is a fine stainless mesh spread over a large area: either a band running right around the inside wall of the pot, or a removable basket. Kyusu makers who work with this tea recommend exactly that combination, and note that the wider mesh area also drains the pot more completely, so the leaf is not left sitting in residual water between infusions.¹²

Try it cold. The same fine leaf that extracts fast in hot water extracts well in cold, and the Japan Tea Central Association names deep steamed sencha alongside gyokuro and upper-grade sencha as the leaf best suited to cold and ice brewing, because it brews strongly.¹³ NARO, Japan's national agricultural research body, recommends an ice-brew method in which leaf and ice are left together in a pot in the refrigerator until the ice melts, and cautions that home-brewed cold tea should be kept refrigerated and drunk within a day.¹⁴ Cold water suppresses caffeine and catechin extraction while amino acids dissolve readily, which is why cold brewing pulls sweetness forward and pushes astringency back.

Store it properly, because tea deteriorates for five specific reasons: humidity, oxygen, light, heat and absorbed odours.¹⁵ The practical advice is to buy in small quantities and finish a packet within two weeks to a month, keep unopened tea in the refrigerator or freezer but bring it back to room temperature before opening it so that condensation does not form on the leaf, and after opening keep it in an airtight, light-proof container somewhere cool and dark rather than in the fridge, where it will pick up moisture and smells.¹⁵

There is a quiet coda to all of this. Shizuoka Prefecture's tea research centre, the institution now developing the cultivars and processing techniques that will shape the next generation of Japanese tea, sits in Kikugawa.¹⁶ The village that could not sell its tea in 1952 is the address where the research still happens.

¹ 農林水産省.「地理的表示登録第130号 深蒸し菊川茶 明細書」. https://www.maff.go.jp/j/shokusan/gi_act/register/0130/pdf/0130_specification.pdf

² お茶百科.「日本の緑茶の主な品種」. 公益社団法人日本茶業中央会. https://www.ocha.tv/how_tea_is_made/plants_and_breeds/plants_and_breeds_japanesetea/

³ 公益社団法人日本茶業中央会.「緑茶の表示基準」令和8年7月10日最終改正. https://www.nihon-cha.or.jp/pdf/hyoujikijyun.pdf

⁴ 消費者庁.「食品表示基準Q&A（新旧対照表）」. https://www.caa.go.jp/policies/policy/food_labeling/food_labeling_act/pdf/food_labeling_cms101_200327_28.pdf

⁵ 鹿児島県.「鹿児島県茶業振興対策資料」. http://www.pref.kagoshima.jp/ag06/documents/24294_20180719104044-1.pdf

⁶ 農林水産省.「第130号：深蒸し菊川茶」地理的表示保護制度登録産品. https://www.maff.go.jp/j/shokusan/gi_act/register/0130/index.html

⁷ お茶百科.「煎茶の製造工程 荒茶工程」. 公益社団法人日本茶業中央会. https://www.ocha.tv/how_tea_is_made/process/schedule_ryokucha/

⁸ お茶百科.「煎茶・深蒸し煎茶」. 公益社団法人日本茶業中央会. https://www.ocha.tv/varieties/nihoncha_varieties/sencha/

⁹ 掛川市.「深蒸し掛川茶の特徴」. https://www.city.kakegawa.shizuoka.jp/gyosei/docs/9103.html

¹⁰ 静岡県経済産業部.「あたらしい農業技術 No.666 静岡抹茶の生産拡大に向けたてん茶安定生産技術の開発」令和2年度. https://www.pref.shizuoka.jp/_res/projects/default_project/_page_/001/054/612/666.pdf

¹¹ 掛川市.「'09掛川スタディ（農林水産省委託事業）」. https://www.city.kakegawa.shizuoka.jp/gyosei/docs/5743.html

¹² 南景製陶園.「茶漉しの選び方」. https://nankei.shop-pro.jp/?mode=f4

¹³ お茶百科.「水出し緑茶のおいしいいれ方」. 公益社団法人日本茶業中央会. https://www.ocha.tv/how_to_brew/nihoncha/reicha/

¹⁴ 農研機構 果樹茶業研究部門.「『水出し緑茶』の上手な淹れ方」. https://www.naro.go.jp/laboratory/nifts/t_contents/mizudashi_ryokucha/irekata.html

¹⁵ お茶百科.「お茶の保存方法」. 公益社団法人日本茶業中央会. https://www.ocha.tv/how_to_brew/how_to_store/

¹⁶ 静岡県農林技術研究所茶業研究センター. https://www.pref.shizuoka.jp/sangyoshigoto/norinjimusho/1046794/index.html