Green tea is produced using an important process of oxidation suppression known sometimes as 'kill the green'. This important step kills leaf enzymes preventing oxidation from occuring, usually by a process of steaming, stir-roasting or baking. The leaves are then often rolled or shaped before drying or firing, a process of removing moisture and fixing the leaf. Good green tea should not brew grey or orange, nor taste dull lifeless or bitter; it should have a pale green to yellow-gold liquor and taste fresh with a sweetness or light astringency.
Water temperature: 70-75C is the optimum for most green tea. Japanese green tea can be brewed as low as 60C (Gyokuro), just be sure to pre-warm the tea ware! Cooler brewing brewing makes tea taste sweeter.
Washing the tea: Optional Chinese practise to remove any dust and impurities and wake up the tea before brewing. To do this steep the leaves in boiling water for 10 secs, swirl and discard the water.
Western brewing: Depending on bulk use 1-2 heaped teaspoons (always 2.5g) per 200ml cup steeped for 2min30s. Use the same leaves for a second infusion using slightly hotter water (75-80C) infused for 2-3 minutes.
Gong-fu style: Use 5-6 grams (4+ teaspoons) per 100ml, repeatedly steeped for short periods, eg. 15-20secs for a first steep (after washing the tea), then increased by 5-10secs each infusion until the flavour has gone. Adjust for personal preference, shorter if too strong, longer if too weak. Best done in a small brewing vessel, eg. under 200ml.
Cold infusion: Infuse 3g in 500ml cold water for 4-6hours for some refreshingly crisp iced tea, or even overnight.