The defining step: fixation
The step that makes green tea green is fixation, sha qing（杀青）, and it happens within hours of picking.
Fresh leaf is heated hard and fast to destroy the enzymes that would otherwise oxidise it.
Polyphenol oxidase is the main target, and above roughly 80°C it stops working permanently.
Once it is gone the leaf cannot turn red, which is the only real difference between green and red tea.
Everything else in the process, including the rolling and the drying, also happens in other categories.
The heat is applied for a few minutes only, since the aim is to stop the enzymes and nothing more.
Hold it too long and the leaf cooks, which produces a yellow leaf and a dull liquor.
Most Chinese green tea is pan-fired or drum-fired at 180°C to 220°C for 3 to 5 minutes.
Japanese green tea is steamed instead, and 30 seconds of saturated steam is enough.
Some teas are basket-fired or dried in the sun, both slower and gentler forms of the same step.
Sun drying leaves enough enzyme activity for the leaf to keep changing, which is how raw pu-erh is made.
Pan-fired versus steamed
Pan firing and steaming do the same job, and they produce teas that taste almost nothing alike.
A pan applies dry heat at 180°C to 220°C, and the leaf is pressed against the metal by hand or by a machine.
That contact drives off water quickly and begins to develop the toasty note Chinese green teas are known for.
Longjing and Biluochun are the clearest examples, and both are shaped in the pan while they are being fixed.
Steaming applies wet heat at 100°C, and the leaf never touches metal at all.
It keeps more chlorophyll, which is why Japanese green tea is a brighter green than Chinese green tea.
It also keeps more of the amino acids, and the cup tastes sweeter and more vegetal as a result.
It leaves more moisture in the leaf, so steamed tea has to be dried for longer afterwards.
Japanese producers vary the steam time deliberately, from 30 seconds for sencha to 2 minutes for fukamushi.
Longer steaming breaks the leaf up more, giving a darker liquor and a softer taste.
Neither method is better, and the choice is one of the oldest regional splits in tea.
Rolling and shaping
Rolling happens after fixation, and it does two separate jobs at the same time.
The first is to break some of the cell walls, so soluble material reaches the surface of the leaf.
That is what gives the liquor its body, and an unrolled leaf brews thin and nearly colourless.
The second job is shape, and green tea has more shapes than any other category.
Longjing is pressed flat against the pan, Biluochun is rolled into a spiral, and Yinzhen is left as a needle.
Each shape changes how the leaf unfolds in the cup and how fast it gives up its material.
A flat leaf releases slowly and evenly, and a tightly rolled one needs the first infusion before it opens.
Pressure is the control, and it is graded from light to heavy depending on the leaf.
A bud grade is rolled lightly or not at all, since heavy rolling would shred it and cloud the liquor.
A coarse leaf is rolled harder, because it has more structure and releases less easily.
Rolling is also where most of the breakage happens, and broken leaf brews bitter rather than strong.
Final drying
Drying is the last step, and it is less simple than it sounds.
Most green tea is dried in two stages, with a rest of an hour or more between them.
The first pass removes the surface moisture at 100°C to 120°C and stops the leaf going soft.
The second finishes the job at 80°C to 100°C, taking the moisture down to 5 or 6 per cent.
Two passes are used because a single hard drying scorches the outside while the inside stays wet.
That produces a tea which smells toasty in the bag and tastes flat in the cup a few months later.
Too gentle a drying leaves too much moisture, and above 7 per cent the tea loses its aroma quickly.
It also risks mould in storage, which is the commonest reason a green tea spoils.
Some producers add a final pan firing for aroma, which is where a deliberately toasty style comes from.
That is a choice rather than a fault, though it is often used to cover leaf picked too late.
Once the tea is dry it should be cooled and packed quickly, since warm leaf absorbs moisture from the air.