# Recent Advances in Volatiles of Teas
## 2 Aromatic Volatile Compounds in Various Kinds of Teas
### Variation of Aromatic Volatiles between Various Kinds of Tea  
White tea, green tea, oolong tea, black tea and Pu-erh tea are major teas consumed in China. White tea is a minimally-processed tea. Fresh tea shoots with abundant leaf trichomes are withed under natural ambient conditions for a few days and then solar dried. The final product looks whitish owing to the dense grey white leaf trichomes covering the tea shoots. Green tea is an unfermented tea. During green tea processing, fresh leaves are heated in a steamer or a hot pan to inactivate the polyphenol oxidase so as to prevent tea polyphenols from oxidation. The fixed leaves are then rolled and dried. Green tea contains a high level of tea polyphenols. Black tea is a fully-fermented tea prepared by a processing procedure \"withering--rolling--fermentation--drying\". Fresh leaves are withered in hot air and rolled in a cylindrical rolling machine or a machine called a CTC (crush, tearing and curling). The rolled leaves are fermented under controlled temperature and humidity, during which the tea polyphenols are oxidized by the polyphenol oxidase enzyme, resulting in the formation of red and orange tea pigments. Oolong tea is a semi-fermented tea whose processing procedure includes withering, shaking, rolling and drying. The aim of shaking processing is to partially bruise the leaf edge by hand touching or by a rotating drum. The polyphenols in the bruised parts of the leaves are oxidized. Pu-erh tea is a post-fermented tea, and its manufacture includes raw tea processing, fermentation and compressing. Fresh leaves are fixed and rolled as green tea. The rolled leaves are sun-dried and used as raw tea for post-fermentation. The raw tea is made damp and piled up for a few months, during which post-fermentation takes place by the action of mold. The fermented leaves are finally compressed into cakes or bricks. Many aromatic compounds in fresh tea leaves are in the forms of non-volatile precursors or glycosides, which are liberated by glycosidase during tea processing [22]. The aromatic precursors and glycosidase enzymes vary with tea cultivars and processing methods. There are great variations of aromatic volatiles between various kinds of tea owing to the differences in tea cultivar and processing method. There were 133 aromatic volatiles formed during black tea processing, among which there were 48 carbonyls, 30 esters, 25 alcohols, 11 hydrocarbons, 3 phenols, 3 lactones and 13 volatiles of miscellaneous structures [23]. Volatile carbonyl compounds can be formed from the degradation of membrane lipids by enzymatic catalyzation. During black tea fermentation, catechins are oxidized. The oxidized catechins are strong oxidizing agents, which may oxidize other compounds, such as amino acids, carotenoids and unsaturated fatty acids, resulting in the formation of volatile compounds contributing to black tea aroma [24; 25]. Linalool, methyl salicate and C\({}_{6}\)-aldehydes increased appreciably during the rolling and fermentation of black tea, accompanying a decrease in unsaturated fatty acids. _Trans_-2-hexenal is increased with the loss of _cis_-3-hexenal during black tea withering and fermentation [6; 25]. The aromatic volatiles are changed with the black tea fermentation, and so, the optimum fermentation time of black tea can be monitored using an electronic nose fitted with quartz crystal microbalance sensors [26; 27]. There are two kinds of green tea, _i.e._, steamed green tea made in Japan and pan-fired green tea made in China. All green teas contain high levels of indole pyridine, linalool, geraniol, benzyl alcohol, 2-phenyl-ethanol, 2-ethylhexanoic acid and maltol. Sulfinyllbismethane and sulfonyllbismethane are considered to be important volatiles contributing to the typical aroma of green tea.