Heat, time, and leaf moisture at the kill-green stage
Kill-green temperature, duration and leaf moisture are the first place to look when a green tea is dull or grassy. The leaf needs to lose roughly fifteen to twenty percent of its weight at this step, but it must not scorch at the edges.
A wok-fired kill-green typically runs at 200 to 220 °C for two to four minutes. Drum and hot-air systems use slightly lower temperatures with a longer residence time, usually 130 to 150 °C for three to six minutes.
The window is narrow. A drop of ten degrees moves the leaf from cleanly fixed to slightly stewed. A rise of the same amount scorches the edges and gives the tea a roasted note that fights the fresh character.
Skilled operators read the leaf by sight and smell rather than by the thermometer. The leaf surface should look bright and slightly glossy, not dull and definitely not brown.
Hand wok operators often use a cloth wipe to test the leaf mid-fixation, pressing a small pinch against the back of the hand. A cleanly fixed leaf feels dry and slightly papery. An under-fixed leaf still feels damp and slightly sticky.
Premium lots usually run kill-green at 200 to 210 °C, ten degrees lower than bulk production, which keeps the amino acids intact and lifts the cup sweetness by five to ten percent.
How tightly the leaf gets rolled
Rolling pressure is the second decision that quietly shapes the cup. Tight rolling packs the cell walls closer together and slows extraction, which gives a more delicate, sweeter first infusion.
Looser rolling gives a faster extraction and a bolder, more immediate cup. Both are valid; they are not the same tea.
Hand rolling can produce a tightness that no machine has matched. A well hand-rolled Longjing, for example, holds a tight flat shape that survives long storage and unfurls slowly in the glass.
Machines give consistency and volume. For most everyday grades that is a fair trade. For premium grades it is part of why hand work still commands a three to ten times price premium.
Drying temperature and the gap between first and second firing
Drying is usually two firings with a rest between. The first brings moisture down from roughly sixty percent to about twenty percent. The rest, which can be twenty minutes to two hours, lets moisture redistribute inside the leaf so the second firing can finish evenly.
Skipping the rest gives a leaf that looks dry outside but still has moisture trapped inside. Within four to six weeks of storage, that trapped moisture starts moving again and the tea loses its clean character.
Second firing temperatures are lower than first firing, typically 100 to 130 °C, and run longer. The aim is to drive off the remaining water without scorching the surface again.
For pan-fired greens like Longjing, the second firing is also when the leaf gets its final polish in the wok. For steamed Sencha, second firing is a hot-air step that brings moisture down without re-firing the leaf.
Drying ends when moisture in the leaf is around five percent. Above seven percent, mould risk in storage rises sharply. Below three percent, the leaf starts to lose aromatic compounds and tastes flat. The two-to-five-percent range is the safe zone.
Where most quality problems actually start
Most quality problems in finished green tea can be traced to one of three places: a slightly late or uneven kill-green, an over-tight rolling, or a drying step that did not give the leaf enough rest.
A dull, slightly brown leaf usually means the kill-green was either ten degrees too cool or thirty seconds too short. Astringency that does not soften in the cup usually points to over-rolling by five to ten percent. Aroma that fades within three months of purchase points to incomplete drying.
Each of these problems is fixable in principle but rarely fixed in practice. Once the leaf has gone through the full process, there is no second chance.
If you are tasting a range of green teas from a single factory, the differences between grades are usually these three variables. The premium tiers are the lots where each variable was held in its narrow window, usually within five percent of an ideal target.
A fourth variable that matters is the time between plucking and kill-green. Premium lots reach the fixer within two to three hours. Bulk lots often wait eight hours or more, and the difference shows in the cup as a flatter, slightly grassy top note.