Aroma Characteristics of Various Teas

The process used to make each type of tea affects the aroma compounds present in the final product. For example, green tea is made by pan-firing or steaming tea leaves, while semi-fermented tea, like oolong and pouchong tea, is made through a fermentation process. The aroma of these teas is highly valued, and certain compounds like jasmine lactone and geraniol play a significant role in determining the aroma of the tea.

Green Tea

To make green tea, the enzymes in freshly plucked tea leaves must be deactivated. This is done by either pan-firing or steaming the leaves, which results in pan-fired or steamed green tea.

Pan-fired green tea

Kosuge et al. (1981) studied the differences in the aroma of Chinese and Japanese pan-fired green teas. They found that Chinese pan-fired green teas had less of certain compounds like geraniol, 2-phenylethanol, benzyl alcohol and phenol, and more of other compounds like linalool oxides, (Z)-3-hexenyl hexanoate, and 2,6,6-trimethyl-2-hydroxy cyclo-hexan-1-one compared to Japanese pan-fired green teas.

Longjing tea is a famous green tea from China that is made by manual pan-firing. Kawakami and Yamanishi (1983) analyzed the aroma components of Longjing tea and found higher concentrations of linalool, linalool oxides, geraniol, 2-phenylethanol, lactones and pyrazines.

You et al. (1992a) investigated the effect of the “tan-fang” treatment on the aroma formation of Longjing tea, which is the first step of making Longjing tea. They found that the “tan-fang” process increased the amounts of volatile compounds in tea leaves, including linalool, its oxides, geraniol, 2-phenylethanol, and methyl salicylate. The “tan-fang” process is important for developing the characteristic aroma of Longjing tea.

Steamed green tea

Steamed green tea is characterized by freshness, naturalness, and briskness. The briskness and freshness are attributed to (Z)-3-hexenol and its esters, such as hexanate and (E)-2-hexenoate. Other components that contribute to the aroma of spring green tea include indole and dimethylsulfide. Gyokuro, the best Japanese green tea, has high levels of ß-cyclocitral, 2,6,6,-trimethyl cyclohexanone, 2-pentenol, 2,4-heptadienal, and 5-octadien-2-one. However, in Japan, a roasted flavor is not preferred in steamed green tea. Roasted flavor is mainly caused by pyrazines, pyrroles, and furans, which are suppressed by microwave treatment. Microwave treatment is effective in preparing green tea that has a refreshing aroma and low astringency.

Scented tea

Scented tea, such as jasmine tea, is produced by scenting steamed green tea with fresh flowers. The main aroma components of jasmine tea are (Z)-3-hexenyl benzoate, benzyl acetate, linalool and methyl anthranylate. Other scented teas, like Youzi tea scented with fresh flowers of Citrus grandis L., contain linalool, nerolidol, (E,E)-farnesol, methyl anthranilate, phytol, etc. Similarly, tea scented with Zhulan flowers contains (Z)-methyl jasmonate, (E)-methyl jasmonate, linalool, nerolidol, methyl N-methyl anthranilate, cedrol and phytol.

Semi-fermented Tea

Semi-fermented tea, which includes pouchong tea and oolong tea, is made in Taiwan and Fujian. Pouchong tea is lightly fermented while oolong tea is more heavily fermented. Both have a unique floral flavor and pleasant taste that is highly valued. The floral flavor is especially prized and determines their market price.

Pouchong tea

Pouchong tea is a lightly fermented tea from Taiwan with a unique floral aroma and taste. It contains compounds like (Z)-jasmone, jasmine lactone, nerolidol, and methyl jasmonate, as well as esters of (Z)-3-hexen-1-ol, linalool oxides, benzyl alcohol, 2-phenylethanol, α-farnesene, and benzyl cyanides. The processing of pouchong tea includes solar withering followed by indoor withering with a shake-turnover treatment, which increases the concentration of these compounds. Jasmine lactone is considered the key substance responsible for the aroma of pouchong tea.

Oolong tea

Oolong tea contains nerolidol, jasmine lactone, and indole, which are found in higher amounts than in pouchong tea. Additionally, oolong tea contains terpenes such as linalool and a-farnesene. Methyl epijasmonate, a strong aroma compound, was found in varying amounts in oolong tea samples. However, a study found that only small amounts of these compounds were present in brewed oolong tea.

Black Tea

Black tea is produced in different regions such as Darjeeling in India, Uva in Sri Lanka, and Keemun in China, each with its own aroma and color. Keemun tea has a rosy and woody note, Uva tea has a sweet flower-like fragrance with a refreshing green odor, and Darjeeling tea is between these two types of teas. Geraniol is an important component in Qimen (Kemmun) black tea, and methyl jasmonate is the most important component of black tea. The amount of essential volatile compounds, especially linalool and its oxides together with methyl salicylate, is higher in orthodox teas than in CTC teas. Black tea has more (Z)-3-hexenol, (E)-2-hexenyl formate, monoterpene alcohols and methyl salicylate than semi-fermented tea, while semi-fermented tea has more (E)-jasmone+ß-ionone, nerolidol, jasmine lactone, methyl jasmonate, and indole.

Speciality Tea

Post fermented tea

Some teas in China, such as Pu-er cha, Liu-bow cha, and Fu-chuang cha, are made through microbial fermentation, which gives them a “moldy” or “aged” flavor. Pu-er tea contains compounds such as (E)-2-hexenal, (E)-2-pentenal, and (E,Z)-2,4-heptadienal that are produced during the fermentation and drying processes.

Brick tea, also a post-fermented tea, is known as “dark green tea” and has a typical fungus flower flavor. Its aroma compounds, including aldehydes, ketones, and pyrazines, increase during fungal growth.

Goishi-cha and Awa-cha are pickled teas in Japan that contain compounds such as (Z)-3-hexenol, linalool, and methyl salicylate.

Toyama kurocha is another pickled tea produced in Japan that undergoes natural fungal fermentation, increasing the amounts of terpene alcohols and producing methylether phenolic compounds. Solar drying greatly increases aliphatic alcohols, aldehydes, and ketones, and volatile phenolic compounds can be produced from ferulic acid and p-coumaric acid by Aspergillus niger and Leuconostoc mesenteroides.

Smoked tea

Smoked tea is popular in western China and contains aroma compounds like linalool, guaiacol, ß-ionone, geraniol, cedrol, and 6–10–14-trimethyl-2-pentadecanone. These compounds are derived from the original compounds in tea leaves, secondary products produced during manufacturing, and fumigating materials absorbed by the tea. Shen and Yang (1989) found that the smoky flavor of smoked black tea made with small leaves is due to compounds like 5-methyl furfural, phenol, o-cresol, p-cresol, guaiacol, 2,6-dimethyl phenol, 4-ethyl guaiacol, 2,6-dimethyl guaiacol, and anthracene.

Herbal Tea

Kawakami and Kobayashi (1991) studied the volatile components of green mate and roasted mate from South America. They found 196 new compounds among 250 volatile components in mate, including common compounds in Camellia sinensis tea such as terpene alcohol, linalool, a-terpineol, geraniol, nerolidol, and ionone-related compounds. Roasted mate contained more furans, pyrazines, and pyrroles formed by the Maillard reaction. Rooibos tea has guaiacol, 6-methyl-3,5-heptadien-2-one, demascenone, geranylacetone, ß-phenyl ethyl alcohol, and 6-methyl-5-hepten-2-one as major components. With brewed extraction, 50 components were found, and with SDE method, 123 components were identified, including 42 new ones. Tengcha, a medicinal tea from China, has a unique aroma consisting of (E)-2-hexenal, (Z)-3-hexenyl hexanote, benzyle acetaldehyde, α-ionone, (Z)-jasmone, cedrol, and 6–10–14-trimethyl-2-pentadecanone.