Introduction to black tea aroma
Tea is the most consumed aromatic beverage of plant origin worldwide. Of the six types of tea (black, green, white, yellow, oolong, and black), black tea is the most produced and consumed, accounting for about 75% of global tea consumption. Black tea does not grow naturally, but is made from green tea. The processing steps for black tea are very different from other teas and include picking, withering, rolling, fermentation and drying. Fermentation occurs in both the rolling and fermentation steps, and is the key process that determines the flavour and quality of black tea. The earliest black tea in China was invented by tea farmers in the Wuyi Mountain tea region of Fujian Province during the Ming Dynasty.

There are more than 400 kinds of aroma substances in black tea. Black tea has a variety of aromas, such as sweet, honey, floral, fruity and roasted. Among them, sweet aroma is the typical aroma category of most black teas, while floral and fruity aroma are more advanced odours compared with the sweet aroma of black teas, which give black teas a better aroma quality. Re-rolling treatment is beneficial to improve the aroma quality of black tea.

Fermentation affects the formation of black tea aroma compounds
Fermentation is the key to shaping the flavour quality of black tea. Through fermentation, the aroma of tea gradually changes from a strong grassy odour to a sweet, floral or fruity one. Volatile compounds in tea can be divided into two groups according to their aroma characteristics: Class I compounds mainly include fatty acid derived volatiles (FADV), especially C6-C9 alcohols and aldehydes, which present an undesirable green or grassy flavour. Class II compounds consist mainly of amino acid-derived volatiles (AADV), volatile terpenoids (VT) and carotene-derived volatiles (CDV), which usually present sweet, floral or fruity flavours. The flavour of tea is closely related to the flavour index (FI), which is the ratio of the total content of class II compounds to the total content of class I compounds.

During fermentation, the degradation of carotenoids, especially ꞵ-carotene, leads to the formation of violet ketones and terpene carbonyls, as well as an increase in linalool. At the same time, grassy/green flavours were suppressed, fruity, floral and characteristic flavours increased with fermentation. Concentrations of geraniol, phenylethanol, trans-linalool oxide (furanin), and benzyl alcohol increased with fermentation, while concentrations of methyl salicylate, linalool, and 1-octen-3-ol decreased. The increase in fermentation temperature accelerated the oxidative hydrolysis of glycosidic aromatic compounds such as phenethyl and benzyl alcohol. The increased content of organic acids, especially acetic acid, is a key precursor for the production of volatiles, especially esters.

Higher fermentation temperatures can promote the total content of volatiles in black tea, especially olefins, alcohols, and some ketones and esters. Specifically, the content of linalool and its oxides, α-pinene, β-laurene, α-laurene, α-cocoene, and ionones can be effectively increased by increasing the fermentation temperature.

Misconceptions about black tea
The redder the tea soup, the better
Black tea is a fully fermented tea, named after the red colour of the tea broth and leaf base. This is due to the chemical reaction that occurs during the processing of tea leaves, so that the chemical composition of the fresh leaves change a lot, and the tea polyphenols reduced by more than 90%, resulting in theaflavin, thearubigin and other new components, and aroma substances than the fresh leaves increased significantly.

Drinking black tea can nourish the stomach
Compared with unfermented and semi-fermented tea, black tea is mild in nature, relatively weak in irritation, and tastes sweet and smooth. After full fermentation, tea polyphenols can be converted by polyphenol oxidase to produce theaflavins, thearubigins, etc., forming the unique flavor of black tea. On the premise of avoiding too much tea, soaking for too long, and having too strong tea flavor, drinking black tea appropriately can reduce the burden on the gastrointestinal tract, but it cannot nourish the stomach.

Black tea can be drunk at night
It is generally believed that green tea has a refreshing effect, and fully fermented black tea, if drunk before bed, will not affect sleep. In fact, this is not the case. This is because caffeine is highly stable, and tea leaves are basically not affected by high temperature, humidity, or even microbial effects during processing. Studies have shown that many varieties of black tea have higher caffeine than green tea. If you drink too much black tea at night, it is easy to affect your sleep quality, and long-term drinking will have adverse effects on your health.

Tips for drinking black tea
Black tea is sweet and warm, which can nourish the human body's yang energy, but it is not recommended to drink it too strong, because the tea contains more tannic acid. Too strong tea soup contains more tannic acid, which can easily affect the body's digestion and absorption of nutrients. Black tea and milk are the best "partners". Milk can make black tea softer and suitable for more people. Although black tea has a softer taste than green tea, oolong tea, etc., it is not a sleep-aid tea, and people who are prone to insomnia should drink it with caution.

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