Growing
Oishita saibai (shade growing)
Covering the field for a set period before harvest to cut out sunlight. Gyokuro, tencha and kabusecha are all grown this way. In sunlight the leaf breaks theanine down while building catechins; keeping the plant dark preserves the theanine and slows catechin accumulation. How long and how dark decides the grade.
In more detail
The name changes with how dark and how long. About a week of light shading gives kabusecha; twenty days or more at over 90% gives gyokuro; pick under the same conditions and dry without rolling and you get tencha, which is milled into matcha. Gyokuro, matcha and kabusecha are, agriculturally, the same idea at different intensities. Shading is either synthetic cloth laid straight over the bushes or the traditional honzu method — straw and reed screens on a frame — which is held to let light through more gently.