Green tea comes from tea plants that are native to Asia. The part of the plant used for making tea is found in the uppermost shoots. This is where the young, tender new leaves and buds are formed.
The top two leaves and the bud are prized both for their fullness of flavor and their ability to be twisted or rolled into a variety of shapes.
For high-grade sencha, harvesters pluck either the bud or the bud plus the youngest leaf. The top two leaves and the bud are prized both for their fullness of flavor and their ability to be twisted or rolled into a variety of shapes.
For good to average tea, they pick the bud plus the top two leaves. For lower quality teas they pick the two top leaves, the lower leaf below them, plus parts of the twig.
After the leaves are picked they are immediately taken away for processing. Processing for green tea is markedly different than for black teas. To make black tea, the fresh leaf is withered by exposure to air and is broken and left to ferment after picking. For green tea, the leaf is not fermented at all. It is steamed immediately after harvesting to stop the fermentation process.
Sencha is dried after steaming and, when dry enough, rolled into a variety of shapes until it is completely dry.
Most tea harvested in Japan is graded as sencha.
The quality of sencha is, however, highly variable. Quality depends on the tea's origin, the season, and leaf processing techniques that are used.