Tea processing

Tea processing refers to the way freshly picked tea leaves are treated to turn them into drinkable tea. Leaves from the plant known as Camellia sinensis can be turned into any one of more than three thousand different beverages known as tea. The wide variety of tea products that may be produced depends on factors such as where the leaves are grown, which variety of the Camellia sinensis plant is used, and how steps in the tea-making process are applied. While tea as a beverage is thought to have originated in China nearly five thousand years ago, it has grown in importance worldwide. In the twenty-first century, more than 5,300 million metric tons (5.3 billion kilograms) are produced annually.

Background

The English word tea came into use in the 1600s from the Chinese te,which referred to the same beverage. Over the years, the word has been spelled in various ways, including tay, thea, tey, and tee. By the time tea was introduced to France and Great Britain between the 1630s and 1640s, Chinese tea growers had discovered new ways to process the green tea they favored to create a black tea with a deeper flavor and smell that was more stable for packaging and shipping. Black tea became the preferred version in many areas of the world.

Tea is believed to have originated in China in the year 2737 BCE when Emperor Shen Nung, a somewhat mystical figure who is considered the father of Chinese medicine, observed that some leaves from the Camellia sinensis tree had fallen into water being boiled by his servant. Shen Nung decided to try the concoction, thus discovering tea. While the truth of this story might never be known, there is evidence of tea in Chinese tombs dating from the second century BCE.

Tea spread to Japan by the seventh century and was eventually carried to Europe by Portuguese traders in the early 1600s. From there, it spread to the New World. Initially, it was expensive and therefore reserved for the wealthy. Over the next several years, however, it grew in popularity until it became such an important commodity that it was subjected to illegal moneymaking schemes, such as "cutting" it with other less-expensive substances, stealing it, and smuggling it.

Overview

While the most commonly known teas are the green tea favored in Asia and the black tea consumed in Europe, North America, and other areas, several other variations of tea, all of which come from the same tea leaves, exist. The major variations are green, yellow, white, Wulong or oolong, black, and fermented. The method of processing determines the type of tea that results.

Tea leaves all start from the same source, the Camellia sinensis tree, which grows in a number of Asian, African, and South American countries. Factors such as location, altitude, and climate can create variations in the trees as they grow. Despite these variations, all tea processing starts with picking the leaves.

Several techniques are used as part of the tea-making process. Not all types of tea undergo all processes, and this is part of what helps to develop different forms of tea. After tea is picked, usually by hand, the leaves are allowed to wilt, or wither. While this process would happen naturally, tea producers can manipulate the process to get a desired result. In controlled withering, leaves are placed on bamboo mats or another surface. The process eliminates up to half the water in the leaves.

Some tea leaves undergo rolling, a mechanical process that curls the semi-dried leaves. Oxidation is another step. Oxidation is a chemical reaction that occurs when a plant or plant product is injured and exposed to air; for example, oxidation is the reason why apple and banana slices turn brown. In tea processing, oxidation begins when leaves are bruised, rolled, or cut, which frees chemicals called polyphenols. Polyphenols interact with air and change into different forms known as theaflavins and thearubigins, which help determine the taste, aroma, and color of a final tea product. Tea producers use techniques such as heat and moisture to control the rate and extent to which tea oxidizes.

Once tea is fully oxidized (or before oxidation happens if the desired tea does not require it), processors heat the leaves to 150 degrees Fahrenheit (about 65.5 degrees Celsius). This heating may occur in several ways and at various points in the process, which also helps determine the color and flavor of tea. Once tea leaves have been fully processed, they need to be dried. Drying makes tea shelf-stable and helps prevent mold and deterioration. Various methods for drying include oven drying, sun drying, and roasting, all of which affect the taste and color of the final product. Some teas are fermented, which is a more severe form of oxidation accomplished by allowing the oxidation process to go on longer.

Different teas are processed differently. White tea is picked while leaves are still budding. At this point, they are covered in fine white hairs, which give the tea its name. The leaves are lightly steamed and dried. This results in a light-colored tea that is sweeter and contains less caffeine than any other type. Yellow tea, found mostly in China, is produced from white tea buds that are allowed to oxidize until they dry. As its name implies, the brewed tea is yellow in color. It is sweeter and more caffeinated than green tea.

Green tea is popular in Asia and is growing in popularity in other parts of the world. The leaves are not oxidized. Instead, they are withered and dried and then spend time in hot roasting pans. They are rolled, returned to the pans, and then rolled again before being packaged. Green teas are lower in caffeine than black teas.

Oolong (or Wulong) tea requires leaves to be picked at their peak and processed quickly. Leaves are wilted and lightly bruised before oxidation. They are not broken or rolled. Oolong tea has more caffeine than green tea but less than black tea.

Black tea is withered, rolled, oxidized, and dried. The processed leaves are dark in color and richer in flavor than other forms of tea, and they have the most caffeine. The final step for all teas is packaging, either loose—by the ounce or pound—for steeping or in premeasured tea bags.

Bibliography

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Wang, Jie and Zhen Li. "Effects of Processing Technology on Tea Quality Analyzed Using High-Resolution Mass Spectrometry-Based Metabolomics." Food Chemistry, vol. 443, 2024, p. 138548, DOI:10.1016/j.foodchem.2024.138548. Accessed 13 Jan. 2025.