Brick dark tea: a review of the manufacture, chemical constituents and bioconversion of the major chemical components during fermentation

Brick dark tea is a unique brick-formed tea compressed from the older, coarse and rough leaves and branches of Camellia sinensis var. sinensis and C. sinensis var. assamica mainly in Hunan, Sichuan and Yunnan provinces in China. Researches on brick dark tea have become increasingly popular owing to its special health benefits. A series of biochemical reactions occur during the special production-microbial fermentation stage and multitudinous components have been detected. Many of the functional components have been isolated and identified from brick dark tea. In this paper, modern manufacturing techniques about different kinds of brick dark tea and their effects on transformation of the chemical constituents, as well as the chemical components were reviewed and discussed.