From the moment the tea leaf is crushed and bruised in the rollers fermentation commences whereby the cell constituents of the leaf come in contact with air and it begins to change colour immediately and develop quickly a reddish hue. With the absorption of oxygen by the leaf, chemical changes take place. The tannins which are soluble in water decrease in solubility and the crushed leaf develops heat as fermentation progresses. It is during fermentation that the flavor associated with tea is developed. The essentital oil in the juice of the tea leaf on coming into contact with oxygen is developed by enzyme activity. Fermentation in connection with tea manufacture means the decomposition of carbohydrates (organic compounds of carbon and water) by yeasts resulting in alcohol and gas or acid and gas. Fermentation of tea is really oxidization of the tannin in the tea leaf caused by enzymic action. Enzymes occur in all plants and are organic substances which bring about chemical changes and decomposition of other substances such as plant cells without undergoing any permanent change themselves. Enzymes, unlike bacteria, are not living bodies and cannot reproduce themselves. They are generally inactivated by temperatures above 140 F. During the process of fermentation tea tannin which is colourless in its raw state, on becoming oxidized develops into red products which are responsible for the characteristic red colour of tea infusions and account for the strength and creaming down of liquors.