Most black teas are made from maturecamellia sinensisleaves and may be plucked either by hand or by machine. Special black teas like golden bud teas and teas known as “beautiful teas” are carefully plucked by hand to ensure composition and quality. 

Chinese Black Teas

During the withering phase, leaves are withered either naturally or mechanically. In natural withering the leaves are spread on the ground or bamboo racks for 5 to 6 hours with frequent stirring. Mechanized withering takes about 4 hours and uses sieves over brick containers that are heated using hot air circulated from wood fires (this gives Chinese black tea its characteristic smoky flavor). Withering removes about 60% of the moisture from the leaves and allows the leaves to soften, preparing them for rolling.

Indian Black Teas

In India, producers reduce the water content of leaves by spreading the freshly picked leaves out in withering vats. The leaves are spread on grids of metal, jute, or plastic that allow air to circulate. The humidity and temperature are constantly monitored during withering, and after 14-17 hours the moisture content of the leaves will be reduced by 60-70%. 

Once the leaves are withered and softened, they are rolled by hand or by machine to break down the structure of the cells, triggering enzymatic oxidation. 

Black tea is fully oxidized, giving the leaves their characteristic dark hue that brews to a beautiful, deep-reddish-brown liquor. How your black tea is oxidized depends on the traditions of the production region and tea estate. Oxidation is the defining step of black tea production, and it all comes down to some pretty interesting chemistry. During oxidation, the originally colorless polyphenols in camellia sinensis leaves are transformed into theaflavins and thearubigins. It is this breakdown that gives black tea its color and astringency - and also leads to the interesting way your body processes the caffeine in different teas (hint: black tea might not be as caffeinated compared to green tea as you think!). If your oxidation period lasts too long, the tea will develop a thick liquor and a strong, almost fermented taste. Too little oxidation results in a thin liquor and a green or raw infusion. 

Chinese Black Teas

Dependent on the conditions of the day and location, the oxidation process for black teas may last 8-12 hours. During oxidation, the leaves are spread out and covered with wet cloths to further stimulate the enzymatic oxidation reaction. The ambient temperature should be around 72°F. 

Indian Black Teas

Indian black teas are spread out on ceramic or steel trays in a humid environment between 68 and 86°F. For quicker oxidation, the leaves are spread in a thin layer. Alternatively, if the producer is looking for a slower oxidation, the layer will be relatively thick. In modern times, humidity may be controlled by a humidifier to maintain at least 90% humidity. Some first flush Darjeelings may only oxidize for 15-30 minutes! Many teas from Assam, in contrast, will oxidize for up to 4 hours. Either way, this is far less time than it takes to oxidize leaves using the traditional Chinese method. 

Oxidation is halted and residual moisture is removed using various techniques until the moisture content is down to 2-6%. Most methods in China involve blowing warm air through conveyer belts. Indian black teas are placed on conveyors or revolving trays in heated machines. 

At this point in the process, the tea leaves are sorted into different grades and undesirable elements like dust, branches and other residue are removed. In China, higher quality teas are usually hand sifted using a bamboo sieve. In India, the leaves are sorted using vibrating grids of varying sizes placed on top of each other. This keeps the larger leaves on top, intermediate leaves in the middle, and crushed leaves and dust at the bottom. (Fun Fact: In Darjeeling all teas are sorted this way and leaf size is used as an indicator of grade.)

Chinese Black Tea Only

This last, optional stage of the process further reduces moisture content and aids batch standardization. 

Developed around 1860, the Orthodox Method uses a largely mechanized process and is used to produce the higher grade Indian teas. This process includes all the steps mentioned above: Plucking, Withering, Rolling, Oxidation, Drying, and Sorting. These are the same steps used in producing Chinese black teas, but the higher temps and humidity used during oxidation in the Orthodox Method result in the bolder and more astringent tannin we are used to from Indian teas.

Developed in the 1930s, the Crush-Tear-Curl (CTC) method speeds up the oxidation process and increases the quantity and speed of harvest yields. Rather than the more complex Orthodox or Chinese methods for processing black teas, CTC consists only of a quick withering followed by cutting and crushing rather than rolling. The leaves are then further torn apart in a machine called a Rotorvane. Then the leaves are rolled into small beads in a large barrel. Usually the leaves used for CTC teas are of a coarser, inferior quality. This method of course revolutionized the tea industry in much the same way that mechanization changed the world during the Industrial Revolution. Similarly, this revolution in efficiency was at the expense of quality in favor of efficiency, volume, and uniformity. 

Most black teas are made from the tea plant camellia sinensis var. assamica. Assamica is native to both India and the Yunnan Province in China, and it was the discovery ofassamicain India that allowed the British to establish the tea trade in that country. Camellia sinensis var. sinensis, with sinensis referring to China, literally means Chinese tea plant. Today, there are many different cultivars from both var. sinensis and var. assamica grown to produce teas and you will find both varietals in multiple regions. That said, it is safe to assume that if you are drinking a black tea it is likely var. assamica, even if it's not from the Assam region in India!