Fermenter

Theory: Oxidation in black tea processing black tea manufacturing technology essentially involves disruption of the cellular integrity of tea shoots, thereby enabling the mixing up of substrates (polyphenol) and the enzymes (polyphenol oxidases). This results in the initiation of a series of biochemical and chemical reactions with the uptake of atmospheric oxygen and formation of oxidized polyphenolic compounds that are characteristic of tea along with volatile flavor compounds that impart typical aroma to tea. During the oxidation, the enzymes polyphenol oxidase and peroxidase act on other polyphenol to produce theaflavins (TF). These red-orange compounds then react with more polyphenol to produce thearubigins (TR), the chemicals responsible for changing the leaf’s color from green to golden, coppery or chocolate brown. The thearubigins, meanwhile, are also reacting with some of the amino acids and sugars in the leaf, creating the highly polymerized substances that develop into the various and distinctive flavor components. In general, theaflavins contribute to the brisk and bright taste of black tea, while the thearubigins provide thickness in the taste (the mouth feel by the liquor) and color of infusion. As the oxidation process is completed, the oxidizing tea leaf takes a new moniker in Indian/Western tea classification as ‘dhool’. During oxidation, the dhool goes through a predictable series of flavor profiles: brisk, high color, and overall strength. Dhool can be directed into particular style by adjusting the length of time allowed in oxidation in combination with regulating the temperature/humidity of the oxidation chamber. Furthermore, the change of TF/TR ratio with the length of oxidation time can be observed. Enzymatic oxidation process can be divided into four stages;