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Until the middle of the 17th century, China was the sole source of green tea. The leaves were compressed into tea bars, which remained fresh for a long time and these were transported across the world. However, this custom of compressing the leaves was stopped during the Ming dynasty, meaning the tea diminished greatly in quality when exported to Europe. Consequently, local producers found they could preserve the leaves for export by oxidising them (often mistakenly referred to as fermentation). The leaves turned a copper colour and such oxidisation was stopped by drying the leaves. This marked the invention of black tea.
Culturally, it’s Europe that forms the key market for black tea, where social rituals have developed around it. The beverage has also been at the heart of political and economic differences between nations.
The finest black teas are prepared exactly like green teas, from the first two leaves and a bud. The gathered leaves are left to dry for 12 – 18 hours on mesh screens. Following withering, the leaves are rolled in order to break down the cells and to develop the flavour of the tea. This also facilitates the commencement of oxidisation (“fermentation”), helping to develop the taste and aroma compounds. Furthermore, it lends the tea strength and briskness, and the leaves then change colour from green to brown. The shelf life of the tea is greatly extended by oxidation.
Oxidation takes place at temperatures up to 40°C under with humid conditions. The time for ceasing such oxidation is crucial, determined by the intended colour of tea and fragrance. In order to stop oxidation, the tea leaves are exposed to a stream of hot air in a drying oven for about 20 minutes.
The vast majority of substances in black tea are only soluble in hot water, which is why water at near boiling point is used to brew it.
According to the size of leaves, black teas are divided into the following categories – whole leaf, broken leaf grades, fannings and dust. Interestingly, the Chinese refer to black tea as red tea, due to the colour of the resultant infusion.
The caffeine in tea has a slower, longer-lasting effect (approx. 4 - 6 hours) than coffee, where caffeine is released very rapidly (within 15 - 45 minutes), but then the effect drops away quickly. The slower effect of caffeine in tea is caused by the presence of tannins and their partial binding to the caffeine.
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