A different physical problem
Every other preparation in tea is a separation: soluble material leaves the leaf, and the leaf is discarded. Whisked tea has no separation step. Finely milled leaf is dispersed through water and the whole thing is drunk, so the soluble fraction dissolves and the insoluble fraction — most of the leaf by mass — is simply carried along in suspension. That reframes every question. There is no steeping time because there is nothing to remove. There is no under-extraction, only poor dispersion. And nothing is left behind to hide a flaw in the material, which is why the quality of the powder shows so immediately.
Why it settles, and why grind size decides that
Suspended particles sink, and how fast depends steeply on their size — small particles settle very slowly, larger ones noticeably faster. Stone-milled matcha is milled to a very fine particle size for exactly this reason: fine enough and the suspension holds together for the few minutes it takes to drink a bowl. Coarser powder, including tea ground in a domestic blade grinder, settles to a sludge at the bottom while the top of the bowl turns pale and thin. This is also why matcha left standing separates, and why a bowl is drunk promptly rather than sipped over twenty minutes.
Clumps, and why sieving is not optional
Milled tea compacts in storage under its own weight and clings together statically, arriving as aggregates rather than free particles. When water reaches a clump, the outside hydrates first and forms a barrier the water struggles to get through, so the interior stays dry and no amount of whisking disperses it — the clump is being pushed around rather than broken up. Sieving the dry powder first defeats the problem before it starts, and it is the single step most often skipped by people whose matcha is persistently lumpy. It works because dry aggregates break apart easily and wetted ones do not.
What the whisk actually does
A chasen does two jobs simultaneously. Its many fine flexible tines shear through the liquid and break up aggregates, doing mechanically what a spoon cannot because a spoon presents one blunt surface. And the rapid movement drags air into the liquid, generating the fine foam that a well-made bowl of thin tea carries. The conventional brisk forward-and-back motion rather than a circular stir exists because a circle sets the whole bowl rotating with the whisk, at which point relative movement — the thing doing the work — largely stops.
The foam
TeaHQ's own reading of well-attested general knowledge, with no single source behind it.
The foam is a genuine physical structure rather than a sign of effort: air bubbles stabilised at their surfaces by material from the tea, commonly attributed to its saponins and proteins. Its fineness depends on how vigorously and how briefly air was worked in, which is why a fast finish with the whisk held lightly at the surface produces a tighter foam than a slow thorough one. Whether foam is desirable is a matter of style and school rather than of correctness — and thick tea is deliberately made without any, which is the clearest evidence that foam is a choice rather than a quality marker.
Thin and thick are separate preparations
Everyday whisked tea and the thick preparation are not strong and weak versions of one thing. Thick tea uses a much higher proportion of powder to water, is kneaded slowly rather than beaten, is not aerated, and conventionally uses powder sold specifically for it. Its texture is closer to a paste than a drink. Approaching it as ordinary matcha made stronger produces something unpleasant, which is the usual first experience of anyone who tries it without knowing that the motion is different.
Temperature, the one shared variable
Temperature still matters, because the soluble fraction does dissolve and dissolves selectively. Water at the boil takes out the harsh fraction efficiently and there is no recovery — nothing is strained, so a bitter bowl stays bitter and cannot be rescued by shortening anything. Well off the boil is the near-universal recommendation. This is the only conventional brewing variable that survives intact into whisked preparation, and it is the one people most often get wrong on the way in.