What is the difference between black, green and white tea?
They all come from the same plant — Camellia sinensis. The difference is entirely in how the leaves are processed after picking, and specifically how much oxidation they are allowed to undergo.
When a tea leaf is picked and bruised, enzymes react with oxygen and the leaf darkens, much as a cut apple does. Controlling that reaction is what produces different teas.
White tea is the least processed: young buds and leaves are simply withered and dried. Minimal oxidation. Pale, delicate, subtly sweet.
Green tea is heated soon after picking — steamed in Japan, pan-fired in China — which deactivates the enzymes and stops oxidation almost entirely. Grassy, vegetal, sometimes marine.
Oolong is partially oxidised, anywhere from around 10% to 80%, which is why oolongs vary so enormously.
Black tea is fully oxidised, then dried. Dark, malty, robust. Confusingly, it is called red tea in China, after the colour of the liquid rather than the leaf.
Pu-erh is a further category, fermented by microbial action after processing, and it genuinely ages.
Brewing follows from processing. Black tea takes near-boiling water, around 95–100°C, for three to five minutes. Green and white need cooler water, roughly 70–85°C, and shorter steeps — boiling water scorches them and extracts harsh tannins, which is the single most common reason people find green tea unpleasantly bitter.
Caffeine varies more by brewing and leaf grade than by type, so the widespread belief that green tea is always lower in caffeine than black does not hold reliably.
Herbal infusions — chamomile, peppermint, rooibos — are not tea at all, containing no Camellia sinensis.