What Makes Matcha Matcha: Shade, Steam, and Stone

Tea Science｜Author：祥興茶行｜Published：2026-07-18

Three deliberate moves — shading the tea bushes, skipping the rolling step, and grinding slowly on stone — separate true matcha from mere green tea powder. Here is the measurable chemistry behind each one.

Take one tea garden and one row of Yabukita bushes. Drape a shade net over the canopy before harvest, and twenty days later the young leaves you pick will have shifted from bitter and astringent to savory-sweet. There is no mysticism here — just a chain of chemical changes you can put numbers on. The secret of what makes matcha matcha hides in three gates: shade growing, no rolling, and the stone mill.

Gate One: Why Does a Shade Cloth Make Tea Sweeter?

Cut off a tea plant's sunlight and it changes its constitution, the way a person does after retreating into the shade. In a field experiment at the Kanaya tea research station of Japan's NARO (National Agriculture and Food Research Organization), researchers split Yabukita tea plants into three groups — open field (S0), roughly 75–80% shade (S75), and roughly 90–95% shade (S90) — covered them directly for about 20 days before the first-flush harvest, and measured the leaf chemistry plot by plot [1]. The results were unambiguous:

Shading tips the flavor balance toward savory sweetness

· Theanine (the source of umami — think of it as the leaf's natural savoriness) rose markedly: the heavily shaded S90 group ran about 40% higher than open-field leaf [1]. · The non-ester catechins EC and EGC (among the sources of astringency and bitterness) dropped sharply; in the shaded groups, EGC fell to between a third and a fifth of open-field levels [1]. · Chlorophyll (the leaf's green pigment) increased — total chlorophyll in the shaded groups was about 1.7 times the open-field level, which is why matcha is so strikingly green [1].

〔圖〕Molecular structure of L-theanine

L-theanine (the umami compound)

Shading drives the tea plant to accumulate more theanine — the key to matcha's savory sweetness.

Why does chlorophyll climb? Another study traced the mechanism down to the molecular level: shading switches on a battery of chlorophyll-synthesis genes and boosts the relevant enzyme activity, and the finished tea held about 1.6 times the total chlorophyll of open-field leaf [5]. That explains the "more shade, more green" rule of thumb. One caution, though — that study covered plants long-term in a greenhouse, not for the two-to-three-week stretch before a matcha harvest, so it serves as a general principle rather than a direct match.

An honest caveat: the catechins do not all drop together. In that same study, the ester-type catechins ECG and EGCG did not fall — EGCG in the shaded groups actually ran slightly higher [1]. A separate 2022 study reported declines in all four catechins [4], so the two papers disagree on the ester types. The more consistent reading across the literature is that shading mainly suppresses the non-ester catechins EC and EGC, while the ester-type changes are inconsistent — it cannot be compressed into "shading removes the catechins." One more wrinkle: past roughly 75% shade, pushing on to 90% brings diminishing returns for most compounds. "Darker is sweeter" has a ceiling [1].

Gate Two: No Rolling — the Line Between Matcha and Green Tea Powder

Many people assume matcha is simply green tea ground to a powder. The real dividing line is one step: rolling. Standard sencha production kneads and rolls the leaf again and again, rupturing the cells and shaping it into needles. Tencha (碾茶), the raw leaf destined for matcha, deliberately skips rolling — after steam fixing, the leaves are dried flat and whole, then stripped of stems and veins so that only the leaf flesh remains, and only then ground to powder. This sequence — steam fixing, no rolling, drying, fine grinding — is how ISO 20715:2023 and the Japan Matcha Association define matcha (the figures and wording below are drawn from the ISO website summary, an ANSI blog post, and the association's page, not from the standard's full text) [6].

```mermaid flowchart LR A[Shaded young leaves] --> B[Steam fixing] B --> C[Dried without rolling] C --> D[Stems and veins removed] D --> E[Tencha] E --> F[Stone-milled fine] F --> G[Matcha] ```

In other words, grind sencha and you get green tea powder; only ground tencha is matcha — shaded tencha, never rolled, is where the boundary lies [6]. As an aside: the "ceremonial" and "culinary" grades you see everywhere are marketing language, with no official legal grading behind them [6]. The habit of whisking powdered tea into a foam traces back to Song-dynasty whisked tea crossing to Japan and being codified by the tea ceremony — a history you can follow in Song-Dynasty Whisked Tea and The Japanese Tea Ceremony and Sen no Rikyū.

Before the Mill: Tencha Winters Over a Summer — and Ripens

We left tencha freshly made, but it does not head straight to the mill. The tencha behind high-grade matcha is picked only once a year, in spring (the first flush around early May, at the "eighty-eighth night" of the traditional calendar). Once finished, it goes into cold storage — today, temperature- and humidity-controlled refrigerated warehouses; in earlier times, cool mountain storehouses called chagura — and stays there until it is needed, at which point it is ground fresh on a stone mill. The reason: the moment matcha is ground, its surface area explodes and it oxidizes, fades, and drifts off-flavor with remarkable speed. Hence the prized ideal of hikitate — freshly ground, freshly drunk [7].

More interesting still: tencha is not at its best brand-new. Spring-picked tencha rests quietly in the cold through the entire summer, undergoing what the trade calls post-ripening, or maturation: the grassy, green edge of new tea slowly recedes and gives way to roundness and deeper umami. The Tokyo tea cooperative goes so far as to compare this rest to the aging of wine and whisky [7]. That stretch of refrigeration, then, is doing two jobs at once: preservation and maturation.

```mermaid flowchart LR A[May: first flush tencha harvest] --> B[Cold storage maturing over summer] --> C[November: kuchikiri taken from the storehouse] --> D[Stone-milled fresh into matcha] ```

Deep in autumn — around November (the tenth month of the old calendar) — tea masters retrieve the tencha sealed away in spring and grind it on the spot. This is kuradashi, "bringing out from the storehouse." The tea gathering at which the year's new tea jar is ceremonially opened and the new tea served to guests, the kuchikiri no chaji, is known as "the tea world's New Year" — the start of the tea practitioner's year, and its most formal occasion [7]. Which is why matcha's true season is held to fall in late autumn, about half a year after picking — not in the spring when it was harvested.

So how should you store the matcha you take home? Matcha's enemies are light, heat, humidity, oxygen, and stray odors [8][9]. To keep an unopened tin for the long haul, the refrigerator or freezer best guards against oxidation and odor pickup — but watch out for condensation when you take it out. Ideally, move it to the refrigerator a day ahead, then let it warm slowly at room temperature, so the temperature swing cannot condense moisture onto the powder [9]. Once opened, switch to an airtight, light-proof caddy in a cool, dark place with a stable temperature, and finish it within about two weeks to a month for the flavor at its best [8][9].

Gate Three: How Fine Does the Stone Mill Grind? The Science of Particle Size

For matcha to stay suspended in water and whip into a dense foam, the powder has to be extremely fine. A team at Ito En measured the particle sizes produced by different grinding methods: stone mills and ball mills both land at a median particle size of roughly 15–20 μm (micrometers — thousandths of a millimeter), while the method that actually gets below 5 μm is jet milling, not the stone mill [2]. That corrects the oft-repeated claim of "5–10 μm from a stone mill" — the measured stone-mill median actually sits around 18 μm [2].

Particle size decides more than texture. The finer the grind, the rounder the particles and the better they foam — in testing, finely ground matcha produced several times the foam volume of a coarse grind [2]. Another study, which tracked an industrial stirred media mill, found that grinding from a median of about 330 μm down to about 17 μm made the powder brighter, greener, and yellower, and even generated signature matcha aromas such as benzaldehyde and α-ionone [3]. That work used a stirred media mill rather than a stone mill, though, so treat it as a general principle — grind fineness shapes color and aroma — rather than a stone-mill result.

Stone mills are slow — and the slowness earns its keep. The figure you often hear, that a stone mill yields only about 30–40 grams per hour, is industry lore; we found no academic or official primary source to back it. What can be documented is that grinding genuinely takes time: one study notes that ball milling often needs 4 hours or more to reach spec, and sometimes 22 [3]. The virtue of slow, cool grinding is that it avoids the frictional heat that would break down theanine and aroma.

The Bottom of the Cup

References

  1. Sano, T., Horie, H., Matsunaga, A., & Hirono, Y. (2018). Effect of shading intensity on morphological and color traits and on chemical components of new tea (Camellia sinensis L.) shoots under direct covering cultivation. _Journal of the Science of Food and Agriculture_, 98(15), 5666–5676. DOI: 10.1002/jsfa.9112
  2. Sawamura, S., Haraguchi, Y., Ikeda, H., & Sonoda, N. (2010). Properties and Shapes of Matcha with Various Milling Method. _Nippon Shokuhin Kagaku Kogaku Kaishi（日本食品科学工学会誌）_, 57(7), 304–309. DOI: 10.3136/nskkk.57.304
  3. Jiang, Y., et al. (2023). Stirred media mill: A novel efficient technology for improving the physicochemical properties and aroma of matcha. _Powder Technology_, 427, 118783. DOI: 10.1016/j.powtec.2023.118783
  4. Li, Y., et al. (2022). Effect of Shading on the Morphological, Physiological, and Biochemical Characteristics as Well as the Transcriptome of Matcha Green Tea. _International Journal of Molecular Sciences_, 23(22), 14169. DOI: 10.3390/ijms232214169
  5. (2024). Greenhouse covering cultivation promotes chlorophyll accumulation of tea plant (Camellia sinensis) by activating relevant gene expression and enzyme activity. _Frontiers in Plant Science_. PMC11127325
  6. ISO 20715:2023 _Tea — Classification of tea types_（scope，https://www.iso.org/standard/75419.html ）；ISO/TR 21380:2022 _Matcha tea — Definition and characteristics_；日本抹茶協會定義頁（https://matcha.or.jp/en/details/ ）。ISO 標準原文為付費，粒徑與四步定義數值轉引自 ISO 官網摘要、ANSI 官方部落格與日本抹茶協會頁。
  7. 東京都茶協同組合。〈後熟によって美味しくなるお茶「蔵出し茶」のお話〉（碾茶／新茶的低溫貯藏與「後熟／熟成」、口切り「茶の正月」）。https://www.tokyo-cha.or.jp/entry2013/20131115_1604.html
  8. 祇園辻利（京都老舖製茶商）。抹茶專欄〈抹茶の保存方法〉（抹茶最忌光・高溫・濕氣，須密閉保存）。https://shop.giontsujiri.co.jp/blogs/column/matcha
  9. 千茶堂。〈お茶の正しい保存方法と消費期限〉（劣化因子光・熱・濕氣・氧氣・移り香；未開封冷凍最佳、取出防結露、開封後 2 週～ 1 個月內飲畢）。https://shop.senchado.jp/blogs/ocha/20200401_403