The slender stems of bocha and the leaves of leaf hojicha look different as soon as you peer into the teapot. But the two were separated much earlier, before roasting.
We look in turn at labeling standards, regional accounts, and two reports: how kukicha and bocha are defined, how their components differ before roasting, and how heating conditions have differed for stems and leaves.
Kukicha and bocha contain stems separated during finishing
The Japan Tea Central Association’s green tea labeling standards define “kukicha or bocha” as tea containing a high proportion of stems and leaf stalks selected during the finishing of aracha, or unrefined tea, using stem-separating machines and similar equipment. The definition says a high proportion, rather than stems alone.
According to Maruhachi Seichajo in Kaga City, Ishikawa, plucking methods such as “one bud and four leaves,” which take leaves down to the fourth from the tip, include stems in the harvest. Steaming and rolling separate the leaves and stems: leaves become sencha or gyokuro, while stems become kukicha or bocha. In some regions, these are also called karigane or shiraore.
The meaning of a name shifts by place. The company writes that in Kaga City, “bocha” often means roasted tea made from stems, while nationally it seems more often to mean green tea made from stems. Whether the tea is roasted may or may not be implicit in the name.
Stems and leaves differ before roasting begins
Maruhachi Seichajo explains tea’s taste mainly in terms of three components: catechins, which bring astringency and bitterness; amino acids, which bring umami; and caffeine, which brings bitterness. Leaf tea has all three, giving a pronounced taste in which bitterness, astringency, and umami are balanced. Stem tea has less catechin and caffeine but more amino acids, so it has milder bitterness and astringency, with a clean taste and noticeable umami.
A report from the Industrial Research Institute of Ishikawa also compares the amino acid content of stems and leaves before roasting. The stems contained about 1.5 times as much. Amino acids in the tea plant have been reported to turn into catechins in the leaves; the report suggests that more may remain in stems because this reaction occurs less there.
Pyrazines that create roasted aromas arise through the Maillard reaction between amino acids and sugars. The greater supply of starting materials in stems is offered as an explanation for differences after roasting.