Black tea is not a variety of tea in itself. All teas come from the same plant, the tea bush (Camellia sinensis). What sets them apart comes down to a single process: oxidation. You may often hear the word fermentation, but that term is technically incorrect. Black tea is, in short, a tea that has been oxidized through a carefully controlled process.
Oxidation (or fermentation) of black tea
Black tea is produced using one of two methods. The orthodox process takes time and involves several distinct steps to produce a quality black tea. It is widely used in China and India. Teas made this way tend to be superior in flavour and also in terms of health benefits, making them the ones worth seeking out.
The CTC method, on the other hand, is designed to streamline production. The resulting black teas vary in quality. It is worth paying attention to origin and favouring teas from well-known regions: Yunnan, Keemun, and others.
Black tea oxidation: the classical method
The traditional process for producing black tea unfolds in several stages, much like the production of other teas.
Withering
Immediately after harvest, the tea leaves are dried until their moisture content is reduced by half. The leaves are spread out on racks, and warm air at around 25°C is circulated over them. They are turned and stirred regularly throughout. This stage lasts approximately 24 hours.
Rolling the tea leaves
At this stage, the tea leaves are "rolled" to release their essential oils. While this is now largely done by machine, some fine teas are still rolled by hand. These represent some of the highest quality teas available.
Oxidation
This is the most important and most carefully monitored step, from withering through to rolling. Oxidation occurs when the polyphenols in the leaf come into contact with air. It is the same process that causes apples or avocados to brown. These polyphenols are normally protected within cell vacuoles, but are released when the leaf is broken or damaged. The chlorophyll also undergoes a transformation, which alters the pigmentation of the leaves. The longer the oxidation, the darker the tea.
Fixing the oxidation
The final step in the process, fixing involves halting the oxidation. The method is straightforward: the leaves are exposed to a heat source for a set period of time. Once oxidation has been stopped, the black tea is packaged and ready to brew.
CTC
Crush-Tear-Curl is a method designed to reduce production time. Black teas made using this process are generally of lower quality than those produced by the classical method. The CTC method is most commonly associated with tea bags. It is significantly less costly and makes use of broken or damaged tea leaves.
Tea naming conventions
In China, black tea is called red tea, owing to the copper hue the water takes on during brewing. This can cause confusion with rooibos, which comes from an entirely different plant and is therefore an herbal infusion, not a tea.
It is also sometimes referred to as fermented tea, which is a misnomer. Black, white, and green teas all go through essentially the same preparation. It is the oxidation stages and their duration that differ depending on the desired result. Only yellow tea is truly fermented. Pu-erh, for instance, is a tea whose flavour evolves and deepens over time.
Another source of confusion is Oolong. Despite the colour it produces in the cup (Chinese speakers also call it crow tea), it is not a black tea. Its oxidation level sits somewhere between green and black tea, and it contains less caffeine.
Black tea is consumed primarily in the Western world. It is grown in many countries, though most of the production is destined for export. The British remain its greatest enthusiasts.