The fermentation process of special step of black tea manufacturing which it was seen that it is an enzyme process during which the tea juices are oxidized after the cells of the leaf are ruptured and for which oxygen is essential. The object of fermentation is to bring about the changes necessary to make a tea liquor palatable. The liquor of unfermented tea leaf, in which the cells are freshly ruptured has a raw and green taste, which is sometimes described as metallic. During fermentation many complex changes take place, the chief effect of which is to give a mellow character to the liquor. As the process of oxidation and condensation continues, liquors become more color and quality is developed, but beyond a certain point in the fermentation process quality starts to decline with an increasing gain in color. When fermentation has proceeded too far the liquors become soft. Thus by reducing or increasing the period of fermentation, the degree of color and quality can be varied to suit different requirements. If extended, more color and less quality will result; if shortened, less color is combined with more quality. These changes and effects are illustrated by the graph in
Flavor is developed much more rapidly than quality and may completely disappear u fermentation is unduly prolonged. As a rule, it will be found that for the conservation of flavor the shortest possible fermentation is required. Strength is a measure of the soluble matter in the liquor and is therefore mainly influenced by the extent to which the cells of the leaf are bruised and the expression of the sap on to the surface of the leaf. Its development on the fermenting racks appears to be significant only in the case of the early dhools, but after some time insoluble products are formed, which results in the liquor becoming soft. The rate of formation of these compounds increases with temperature.
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