The same job, two ways of doing it
Fixation has one purpose: get enough heat into the leaf, fast enough, to destroy the enzymes that would otherwise brown it. Steam does this by condensing on the leaf surface and transferring a great deal of heat almost instantly, and it does it in seconds. Dry heat does it by direct contact with a hot wok or drum wall, over minutes. Both work. But heat transfer is not the only thing that happens, and the by-products are so different that they produce two traditions which barely resemble each other in the cup. There is a practical difference too. Steam reaches every surface of every leaf at once, so fixation is even almost by construction, whereas a pan or drum fixes whatever happens to be in contact with the hot surface at that moment and relies on tumbling to give every piece its turn. Evenness is the harder problem in dry-heat fixation, and it is where most of the skill goes.
What steam leaves behind
Steaming brings no dry surface with it, so nothing toasts. The leaf keeps a vivid green colour, and the marine, seaweed-adjacent, savoury character that Japanese green tea is known for survives intact, because nothing has been added on top of it. Steam duration then becomes a style axis in its own right: a short steam leaves the leaf structurally whole and gives a clear, delicate, aromatic cup, and a long steam breaks the leaf down considerably, producing a cloudy, deep green, heavy-bodied liquor with less aroma and much more weight. Both are sencha; they do not taste like the same drink. Deep steaming also produces a visible consequence that is routinely misread as a fault. The leaf breaks down into fine particles that pass through a filter and stay suspended, so the liquor is cloudy and dark rather than clear. That cloudiness is the intended result and carries much of the body the style is chosen for, and a drinker who strains it out has removed the reason for buying a fukamushi in the first place.
What the pan adds
In a wok or a heated drum, the leaf surface reaches temperatures at which browning reactions begin, and those reactions produce aroma compounds that were not in the leaf beforehand. The result is the chestnut, roasted grain and nut character running through Chinese green tea, and a liquor that is yellow-green rather than jade. The addition is inseparable from the operation — there is no way to fix a leaf against hot metal without it — which is why a Chinese green tea cannot be made to taste Japanese by adjusting anything downstream, and vice versa. The toasting is also a matter of degree that the maker controls. A cooler wok and a shorter dwell give a lighter, greener result; a hotter one gives more chestnut. And in the highly shaped teas the same contact is doing the shaping as well, so for Longjing the temperature that sets the flat blade and the temperature that sets the aroma are the same decision, taken by feel, continuously, for the length of the batch.
Why the traditions diverged and stayed diverged
Steaming is the older Chinese method; it was carried to Japan and became the standard there, while China moved to pan-firing. Two national tea cultures then developed for centuries around their respective methods — cultivars selected to suit them, shaping techniques built around them, brewing vessels and temperatures adapted to the results, and drinker expectations formed by them. The divergence is now far deeper than the fixation step alone: Japanese production is steam-fixed, machine-harvested, needle-rolled and finished as aracha before refining, while Chinese production is pan- or drum-fixed and shaped in dozens of regional ways. The fork at fixation is where it starts, not where it ends. The divergence extends to what each tradition counts as a fault. A Japanese producer regards any toasted note in a sencha as a defect of drying; a Chinese producer regards its absence in a Longjing as a sign of a machine. Neither is misjudging the other’s tea so much as applying a standard built around a different fixation method, and a great deal of cross-cultural disagreement about green tea reduces to exactly that.
The exceptions, which are worth knowing
Neither tradition is exclusive. Japan makes kamairicha, a pan-fired green tea, mostly in Kyushu, and it tastes recognisably closer to a Chinese green than to sencha. China makes steamed greens — Enshi Yulu is the well-known survivor — and they read as unusually clean and marine to a palate expecting chestnut. Korea sits between the two traditions and uses both. These exceptions are useful precisely because they hold the country constant and vary the method, which is the closest thing the subject has to a controlled experiment. Tamaryokucha is worth adding to the list because it splits the difference deliberately. It is Japanese, it exists in both steamed and pan-fired forms, and it is shaped into a curl rather than a needle — so a steamed guricha and a kamairi-style tamaryokucha differ in fixation while holding almost everything else constant. Anyone wanting to hear what the fixation step alone does could hardly ask for a better pair.
What to do with this when tasting
It gives you a diagnostic. Marine, savoury, vividly green and slightly vegetal points to steam. Chestnut, toasted grain, nutty and yellow-green points to a pan or drum. Once you can hear which fixation method you are tasting, the two national styles stop being an arbitrary list of names to memorise and become one decision with predictable consequences. It also explains a common disappointment: a drinker who loves sencha and is offered a good Longjing frequently finds it tastes cooked, and a drinker who loves Longjing frequently finds sencha tastes of the sea. Both are correct, and both are describing the fixation step. It has a brewing consequence as well. Deep-steamed leaf is broken and extracts fast, so it wants short steeps and a fine-mesh pot; needle-shaped light-steamed leaf and open pan-fired leaf both extract more gradually. That is a difference in particle size rather than in category, and it is why the same water temperature and time applied to two green teas from different traditions can produce one balanced cup and one that is either thin or harsh.