A single granite mill turns at 30 to 40 revolutions per minute. In one hour it produces 30 to 40 grams of powder. That is not a design flaw — it is the bottleneck that defines real Matcha. Everything about the quality of Matcha powder follows from this one fact: why so slow? What happens on those stone discs that would be lost at higher speed? And what does that mean for the green powder in the tin?
Tencha: the starting material no other tea can replace
Before Matcha powder exists, Tencha must exist. Tencha is not a particularly noble tea — it is not a finished product anyone drinks. It is an intermediate stage, optimised specifically for milling.
The crucial difference from Sencha or Gyokuro lies in the drying method. Sencha leaves are rolled after steaming — this rolling process breaks open the cell structure, gives the tea its needle shape, and alters the internal architecture of the leaf. Tencha is not rolled. The leaves are dried flat, in hot air, until they are paper-thin and brittle. The result is flat, fragile leaf fragments with no structure at all — almost like thin green paper.
Before milling, stems and leaf veins are removed. These woody fibres would clog the mill and cannot be ground down to 5–10 micrometres anyway — dimensions that only soft leaf tissue can achieve. What remains is almost pure leaf blade: high chlorophyll content, high amino acid content, minimal fibre.
Why can't Sencha be milled into Matcha? Because the rolling process changes the cell structure and creates a different fibre architecture. The material would not become fine enough during milling, and the flavour would be bitter and flat — the amino acids that accumulate under shading develop differently in rolled tea.
Tencha processing before milling: destemming and ageing
The step between dried Tencha leaves and the mill is more complex than it looks. First, destemming: the brittle leaves are separated by air classification — a controlled airstream that separates light leaf tissue from heavier stems and veins. The leaf flesh is thinner and lighter and is carried along by the current; stems and veins fall out due to their higher density. Between 40 and 50 percent of the original leaf weight is sorted out this way. This fraction is not waste in the industrial sense — it is the raw material for Kukicha, the stem tea.
What remains is exclusively leaf blade: the softest, most nutrient-rich, most millable material the tea plant produces.
Then comes a step that many consumers do not expect: storage. Top productions store Tencha after processing at 5 degrees Celsius — for six months, sometimes up to a year — before the material is milled. This process is called Kuradashi (蔵出し) in Japanese, roughly translating as "release from the storehouse." The controlled cold storage softens astringency, rounds the texture, and deepens the Umami. The precise chemical mechanisms are not yet fully understood, but the effect is measurable in the cup: freshly processed Tencha often has a certain sharpness that recedes noticeably after Kuradashi. For top-grade Matcha, ageing is not an option — it is part of the production strategy.
Particle size: 5–10 micrometres and what that means
High-quality Matcha powder has a particle size of 5 to 10 micrometres. For reference: icing sugar sits at around 30 micrometres. Matcha is therefore three to six times finer than the finest kitchen powder most people are familiar with.
This size is not an aesthetic standard — it has direct physical consequences. Particles below 10 micrometres remain suspended in water without settling. This is due to the interaction between particle size, density, and the Brownian motion of water molecules. Icing sugar dissolves; Matcha particles do not — they float. When you drink it, the entire solid matter passes across the palate, which is what creates the body and texture of the drink.
Industrially milled Matcha, produced in jet mills or hammer mills running at thousands of revolutions per minute, achieves this fineness less reliably. The particle size distribution is broader — more large particles, less uniform suspension. You notice it in the bowl: the powder settles faster, and the texture feels sandier.
Milling: stone vs. industrial — the measurable difference
There is a common simplification: "stone-milled is better than industrially milled." That holds true under certain conditions — but it is worth being more precise.
The difference starts with particle size distribution. Stone milling produces a narrow, symmetrical curve — most particles fall between 5 and 10 micrometres, with little spread in either direction. An impact mill produces a significantly broader distribution: from 3 to 25 micrometres, with more outliers at both ends. This difference matters in practice. Uniform particles form a stable microfoam when whisked with the Chasen — small, even bubbles that dissolve slowly. Uneven particle sizes produce uneven bubbles: the larger particles settle faster, the foam visibly collapses, and the texture in the mouth feels less silky.
Then there is temperature. A granite mill turning at 30–40 RPM generates almost no heat through friction — milling temperature typically stays between 20 and 30 degrees Celsius. A ball mill can reach 60 to 80 degrees; a jet mill creates instantaneous heat spikes at the point of impact, even if the average temperature is lower. These brief heat pulses are problematic for chlorophyll and volatile aromatic compounds, even when overall temperature is controlled.
The third parameter is economic, and it explains why the price difference between real ceremonial Matcha and an industrial café product is so large: a stone mill with one operator produces 30 to 40 grams per hour. At realistic labour costs in Japan, that corresponds to 2 to 3 euros in labour alone for milling a single 30-gram tin. An industrial mill grinds 1 kilogram in a matter of minutes — the pure milling cost per 30-gram unit drops below 10 cents. This is not an argument against industrial milling for the mass market. It is a straightforward explanation of why craft-produced Matcha cannot be cheaper.
For the top quality segment, the stone remains the industry standard — not out of nostalgia, but because the physics are sound.
The heat problem: chlorophyll, pheophytin, and the 40-degree threshold
Here lies the real reason for the stone mill's slow rotation speed. Chlorophyll — the pigment that gives Matcha its characteristic colour — is thermolabile. At around 40 degrees Celsius, a chemical reaction begins in which magnesium is displaced from the chlorophyll molecule. The product is pheophytin: visually a significantly darker, brownish-olive pigment without the brightness of the original chlorophyll.
This is not a matter of taste — it is a measurable chemical reaction. Matcha that becomes too warm during milling does not merely look worse; it is structurally a different product. Temperature control is the core of the argument for the stone.
A granite mill turning at 30–40 RPM generates almost no heat through friction. The mill stays well below 40 degrees Celsius. A high-speed mill at 3,000+ RPM, on the other hand, generates considerable heat through the mechanical energy transferred into the material. Precise temperature control is technically possible with industrial mills — cooling via air supply, pauses between runs — but it is more involved than the simple physics of the slow stone mill.
The colour of fresh high-quality Matcha powder — that intense, almost neon jade green — is a direct indicator that the chlorophyll has remained intact. Olive-coloured or yellowish powder signals pheophytin formation, either from heat during milling or from subsequent oxidation.
Oxidation and shelf life: why the 30-gram tin exists
Ground powder has a problem: surface area. A whole Tencha leaf has a certain surface area in contact with oxygen. The same leaf, milled to 5–10 micrometres, has a total surface area larger by several orders of magnitude — every individual particle is exposed on all sides.
Oxygen attacks primarily the aromatically active compounds: dimethyl sulphide (responsible for the characteristic maritime, slightly oceanic note of high-quality Matcha), β-ionone (a terpene derivative with floral notes), and other volatile aromatic compounds. These oxidation reactions proceed at room temperature within days if the powder is unprotected. This is why Matcha is packaged in nitrogen-flushed tins — the oxygen is displaced from the tin before sealing.
A 30-gram tin is not a marketing decision about price per gram. It is a practical response to the oxidation rate. With regular use (1–2 grams per preparation), a 30-gram tin is finished in three to four weeks — before quality degradation becomes relevant. A 100-gram package would last twelve weeks under real usage conditions. That is too long.
After opening: reseal the tin immediately and store it in the refrigerator. The combination of oxygen, light, and warmth dramatically accelerates oxidation. In the refrigerator the reaction rate slows, and the pressure differential with the outside air keeps moisture out — condensation when taking the tin out is something to avoid, so let it come up to room temperature before opening.
30 grams, incidentally, is roughly one hour of work from a single stone mill. That is not marketing copy — it is the accounting reality of production.
Packaging and protective gas: what the tin actually does
Packaging is not an afterthought — it is part of quality assurance. Before sealing, the tin is flushed with nitrogen: the inert gas displaces the residual oxygen inside the tin and protects the powder from the moment of filling until the first opening. This nitrogen atmosphere is why a freshly opened tin is qualitatively identical to the powder straight off the mill — provided cold storage has been maintained throughout.
The choice of tin material is not arbitrary. Aluminium-lined tins combine three barriers in one: light protection, oxygen barrier, and moisture barrier. Plastic pouches — even high-quality, vacuum-sealed ones — allow more oxygen and UV radiation through over time than aluminium does. Light catalyses the same oxidation reactions as oxygen; direct sunlight on a Matcha tin means accelerated degradation, even if the tin is still sealed.
A more recent development from some top producers: individual nitrogen-flushed single-serve sachets, each containing 1 to 2 grams. The principle is the same, but applied consistently to the individual portion — every preparation uses freshly opened, unoxidised powder. The price per gram is higher, but for Matcha drinkers who prioritise uncompromising freshness, it is a sensible option.
Matcha in water: suspension, not solution
Matcha does not dissolve in water. That sounds like a problem, but it is the mechanism that makes the drink what it is. The particles remain as a solid — they form a colloidal suspension, similar to cocoa in milk or starch in water.
The leaf tissue of Camellia sinensis has a waxy cuticle — a layer of hydrophobic lipid compounds that protects the plant against water loss. This cuticle is preserved in the particles even after milling. Hydrophobic particles in water do not form a stable suspension on their own — they clump together and settle, because the water surface requires energy to interact with the particles.
The Chasen — the bamboo whisk — serves exactly this function: not to stir, but to break the surface tension mechanically. The rapid back-and-forth movements generate local turbulence that tears the particles apart and coats them with water. The resulting foam is not decorative; it is an indicator that the suspension is stable and the particles are evenly distributed.
Why not boiling water? At 100 degrees Celsius, aromatic compounds oxidise quickly, and the elevated temperature also accelerates pheophytin formation in the chlorophyll that has not yet fully degraded. The ideal water temperature is 70 to 80 degrees Celsius — hot enough to stabilise the suspension and mobilise aromas, but below the degradation threshold of the most sensitive compounds.
Lower temperatures work too — cold brew Matcha, with water below 10 degrees Celsius and several minutes of extraction, produces a different suspension that is often perceived as sweeter, because certain bitter compounds are less mobile at low temperatures.
How to recognise freshness: two practical tests
Fresh, high-quality Matcha powder can be assessed with two simple tests that require no equipment.
The first is the paper test. Spread a small amount of powder on white paper, then slowly draw a line through it with your finger. High-quality, finely milled Matcha leaves a smooth, even streak with no visible grain — comparable to the line left by a kohl pencil. Industrially milled Matcha with a broader particle distribution produces a grainy, uneven streak with visible particles breaking out of the line. The difference is visible to the naked eye.
The second test checks suspension stability. Whisk two grams of Matcha into 70 millilitres of water at 80 degrees, then set the bowl down without further movement and observe. Good Matcha stays homogeneously suspended for at least 60 seconds before the first particles begin to show at the bottom. Industrially milled Matcha often starts to visibly sediment after just 15 to 20 seconds — a direct effect of the broader particle size distribution and poorer surface wetting. Once you have done this test, you notice the difference during normal drinking too: the faster settling, the changed texture in the last sip.
What happens between the Tencha leaf and the bowl is not a mystical process. It is materials science: particle physics, thermochemistry, oxidation kinetics. Understanding these mechanisms explains why real Matcha powder is the way it is — and why shortcuts in production lead to differences that are both measurable and tasteable. At UNEARTHED, we carry exclusively stone-milled Matcha from producers where these parameters are known and documented.
