The Principles of Tea Manufacture Part 4

摘要

Infused Leaf. - The colour of the infused leaf is regarded by the trade as a factor of some importance in judging the quality of a tea. Whether this is entirely justifiable is open to some doubt, but in the ordinary course of orthodox manufacture, examination of infused leaf can give useful information. For instance, if the dry leaf is apparently small but appears as large pieces on the lid of the pot after cupping it is certain that it has been well and tightly twisted. The actual colour of the infused leaf is, curiously enough, due to a side reaction which cannot apparently have any direct effect on the quality of the liquor and which probably can be misleading. When the enzyme oxidizes the catechins or oxidizable matter the first product is a highly reactive compound known as a quinone. It may be said to be similar to hydrogen peroxide and is in fact an oxidizing agent in its own right. As explained earlier it is the initial step in the condensation reaction. The quinones almost instantly reacteither together or with unchanged oxidizable matter, but if, during the course of their brief existxence they come into contact with the green colouring matter in the leaf known as chlorophyll, they oxidize it to a brown pigment and the green colour of the leaf changes to brown.