All tea comes from the camellia sinensis plant. While varietal and terroir influence tea outcome, it’s the method of processing that defines the type of tea and has dramatic impact on body, aroma, and flavour.
White is fully wither dried, unprocessed, not oxidized. It is typically presented as buds or two leaves and a bud.
The objective of withering is to reduce the moisture in the tealeaf by up to 70% (varies from region to region). Tea is laid out on a wire mesh in troughs. Air is then passed through the tea removing the moisture in a uniform way. This process takes around 12 to 17 hours. At the end of this time the leaf is limp and pliable and so will roll well.
Tea is placed into a rolling machine, which rotates horizontally on the rolling table. This action creates the twisted wiry looking tealeaves. During the rolling process the leaves are also broken open, which starts the third process - oxidization.
Once rolling is complete, the tea is either put into troughs or laid out on tables whereby the enzymes inside the tealeaf come in to contact with the air and start to oxidize. This creates the flavour, colour and strength of the tea. Think of how a sliced apple turns brown soon after it has been cut. This is oxidization. It is during this process that the tealeaf changes from green, through light brown, to a deep brown, and happens at about 26 degrees centigrade. This stage is critical to the final flavour of the tea, if left too long the flavour will be spoiled. Oxidization takes from between half an hour to 2 hours. This process is monitored constantly with the use of a thermometer along with years of experience. The tea then passes to the final stage of drying.
To stop the oxidizing process the tea is passed through hot air dryers. This reduces the total moisture content down to about 3%. The oxidization will be stopped by this process, and now the dried tea is ready to be sorted into grades before packing.
The main difference when making green tea is that the oxidization process is omitted, which allows the tea to remain green in colour, and very delicate in flavour. In order to ensure that the freshly picked leaf does not oxidize, before the tea is rolled, the leaf is either pan fried, or steamed. This will prevent the interaction of the enzymes in the leaf, and so no oxidization can take place. In China some green teas are withered before being pan fried, but more usually in green tea manufacture, the withering process is omitted as well. Rolling, drying, and sorting follow.