Black tea is not a variety of tea. All teas come from the same shrub, the tea plant (Camellia sinensis). Their name is due to a single phenomenon: oxidation. Certainly, we often hear about fermentation, but the term is incorrect. Black tea is therefore an oxidized tea thanks to a very specific process.
Oxidation (or fermentation) of black tea
The production of black tea has two methods. The orthodox process, which takes its time and requires several steps to obtain a quality black tea. It is found a lot in China and India. Better in taste, but also for health, these are the teas you should favor.
The CTC method, on the other hand, consists of optimizing production. This can produce black teas of varying quality. So be careful about the origin and prefer teas from known provinces: Yunnan, Keemun, etc.
Black tea oxidation: classic method
The traditional process for making black tea takes place in several stages (just like for other teas).
Withering
Right after harvesting, the tea leaves are dried, until their moisture content is reduced by half. For this purpose, grids are used on which the leaves are spread, and air is blown at a temperature of 25 degrees. The leaves are, of course, turned and stirred regularly. This stage lasts about 24 hours.
Rolling of tea leaves
Here, the tea leaves are "rolled" in order to extract the essential oils. While this operation is now performed by a machine, some great teas are still rolled by hand. These are very high-quality teas.
Oxidation
This is the most important and most controlled step, from withering to rolling. Oxidation occurs when polyphenols come into contact with air. It's the same phenomenon as with apples or avocados. These polyphenols are normally protected by vacuoles, except when there is a "break". Chlorophyll also undergoes a transformation, changing the pigmentation of the tea leaves. The more a tea is oxidized, the blacker it will be.
Fixing the oxidation
The final step of the process, fixing consists of stopping oxidation. The method is simple. The tea leaves are exposed to a heat source, for a longer or shorter time. Once the oxidation is stopped, the black tea is packaged and ready to be consumed as a beverage.
CTC
The Crush-Tear-Curl, literally Crushing-Tearing-Rolling, is a method that aims to reduce production time. The black tea concerned by this manufacturing method is generally of lesser quality than that which has received a classic treatment. It is often intended for tea bags. The cost of this method is much lower and allows the use of damaged tea leaves.
Tea naming
In China, black tea is called red tea, because of the copper color that the water takes during infusion. This can lead to confusion with rooibos, which comes from a different plant and is therefore not a tea, but an infusion.
They may also call it fermented tea, which is a mistake. Indeed, black, white, or green teas have the same preparation. It's the oxidation steps and their duration that change depending on what you want to obtain. Only yellow tea is fermented. For example, Pu-Erh is a yellow tea with a taste that changes over time.
Another case of confusion is Oolong. Despite its color after infusion (the Chinese also call it raven tea), it is not a black tea. Its oxidation is between green tea and black tea. It is also less rich in theine.
Black tea is mainly consumed in the West. Its cultivation is practiced in many countries, however, it is mainly intended for import. The English are, in fact, those who drink the most.