Tea originated in Southwest China, where it was used as a medicinal drink. It was popularized as a recreational drink during the Chinese Tang dynasty, and tea drinking spread to other East Asian countries. Portuguese priests and merchants introduced it to Europe during the 16th century. During the 17th century, drinking tea became fashionable among Britons, who started large-scale production and commercialization of the plant in India to bypass the Chinese monopoly.
The term herbal tea refers to drinks not made from Camellia sinensis: infusions of fruit, leaves, or other parts of the plant, such as steeps of rosehip, chamomile, or rooibos. These are sometimes called tisanes or herbal infusions to prevent confusion with tea made from the tea plant.
Processing and classification
Tea is generally divided into categories based on how it is processed. At least six different types are produced:
• White: wilted and unoxidized
• Yellow: unwilted and unoxidized but allowed to yellow
• Green: unwilted and unoxidized
• Oolong: wilted, bruised, and partially oxidized
• Black: wilted, sometimes crushed, and fully oxidized
• Post-fermented: green tea that has been allowed to ferment/compost
The most common are white, green, oolong, and black. After picking, the leaves of C. sinensis soon begin to wilt and oxidize unless immediately dried. An enzymatic oxidation process triggered by the plant's intracellular enzymes causes the leaves to turn progressively darker as their chlorophyll breaks down and tannins are released. This darkening is stopped at a predetermined stage by heating, which deactivates the enzymes responsible. In the production of black teas, halting by heating is carried out simultaneously with drying. Without careful moisture and temperature control during manufacture and packaging, growth of undesired molds and bacteria may make tea unfit for consumption. Although single-estate teas are available, almost all tea in bags and most loose tea sold in the West is blended. Such teas may combine others from the same cultivation area or several different ones. The aim is to obtain consistency, better taste, higher price, or some combination of the three. Tea easily retains odors, which can cause problems in processing, transportation, and storage. This same sensitivity also allows for special processing (such as tea infused with smoke during drying) and a wide range of scented and flavoured variants, such as bergamot (found in Earl Grey), vanilla, and spearmint.
Popular varieties of black tea include Assam, Nepal, Darjeeling, Nilgiri, Rize, Keemun, and Ceylon teas. Many of the active substances in black tea do not develop at temperatures lower than 90 °C (194 °F). As a result, black tea in the West is usually steeped in water near its boiling point, at around 99 °C (210 °F).. Since boiling point drops with increasing altitude, it is difficult to brew black tea properly in mountainous areas. Western black teas are usually brewed for about four minutes. In many regions of the world, however, actively boiling water is used and the tea is often stewed. In India, black tea is often boiled for fifteen minutes or longer to make Masala chai, as a strong brew is preferred. Tea is often strained while serving. A food safety management group of the International Organization for Standardization (ISO) has published a standard for preparing a cup of tea (ISO 3103: Tea — Preparation of liquor for use in sensory tests), primarily intended for standardizing preparation for comparison and rating purposes.
In regions of the world that prefer mild beverages, such as the Far East, green tea is steeped in water around 80 to 85 °C (176 to 185 °F). Regions such as North Africa or Central Asia prefer a bitter tea, and hotter water is used. In Morocco, green tea is steeped in boiling water for 15 minutes. The container in which green tea is steeped is often warmed beforehand to prevent premature cooling. High-quality green and white teas can have new water added as many as five or more times, depending on variety, at increasingly higher temperatures.
Flowering tea or blooming tea is brewed at 100 °C (212 °F) in clear glass tea wares for up to three minutes.
Oolong tea is brewed around 82 to 96 °C (185 to 205 °F), with the brewing vessel warmed before pouring the water. Yixing purple clay teapots are the traditional brewing-vessel for oolong tea which can be brewed multiple times from the same leaves, unlike green tea, seeming to improve with reuse. In the Chinese and Taiwanese Gongfu tea ceremony, the first brew is discarded, as it is considered a rinse of leaves rather than a proper brew.
Premium or delicate tea
Some teas, especially green teas and delicate oolong teas, are steeped for shorter periods, sometimes less than 30 seconds. Using a tea strainer separates the leaves from the water at the end of the brewing time if a tea bag is not being used. However, the black Darjeeling tea, a premium Indian tea, needs a longer than average steeping time. Elevation and time of harvest offer varying taste profiles; proper storage and water quality also have a large impact on taste.
Pu-erh teas require boiling water for infusion. Some prefer to quickly rinse pu-erh for several seconds with boiling water to remove tea dust which accumulates from the ageing process, then infuse it at the boiling point (100 °C or 212 °F), and allow it to steep from 30 seconds to five minutes.
Cold brew and sun tea
While most tea is prepared using hot water, it is also possible to brew a beverage from tea using room temperature or cooled water. This requires longer steeping time to extract the key components, and produces a different flavor profile. Cold brews use about 1.5 times the tea leaves that would be used for hot steeping, and are refrigerated for 4–10 hours. The process of making cold brew tea is much simpler than that for cold brew coffee. Cold brewing has some disadvantages compared to hot steeping. Firstly, if the leaves or source water contain unwanted bacteria, they may flourish, whereas using hot water has the benefit of killing most bacteria. This is less of a concern in modern times and developed regions. Secondly, cold brewing may allow for less caffeine to be extracted Sun tea is made by steeping the tea leaves in a jar of unheated tap water left in the sun. It does not get hot enough to kill bacteria present on the tea leaves or in the water, such as Alcaligenes viscolactis.
To preserve the pretannin tea without requiring it all to be poured into cups, a second teapot may be used. The steeping pot is best unglazed earthenware; Yixing pots are the best known of these, famed for the high-quality clay from which they are made. The serving pot is generally porcelain, which retains the heat better. Larger teapots are a post-19th century invention, as tea before this time was very rare and very expensive.
The Chemical Composition of Tea
The tea leaf itself is packed with different compounds, the main ones being polyphenols, which can be up to 40% of the dry weight of the leaf. There are also amino acids, enzymes, methylxanthines such as caffeine, minerals and vitamins and more than 700 aroma compounds in trace amounts.
Polyphenols – also known as tannins – are by far the largest group of compounds in tea. In a cup of tea, they largely provide astringency, that dry-mouth feeling after a drink, while also providing some colour and flavour. They are believed to have disease-busting antioxidant properties. A strong cuppa can have as much as 240mg of polyphenols. The most important group of polyphenols in tea are the flavonoids, featuring flavanols that include a variety of catechins, with epigallocatechin gallate being widely studied for its health benefits. Much of the flavour and colour of a cup of tea results from the two phenolic substances theaflavins and thearubigins, which are formed from flavanols during tea processing. There is limited knowledge about these compounds but much research is being done. Other types of flavonoids, such as flavones and anthocyanins, are also found in tea. Besides the health-boosting antioxidants, tea is well known for its stimulant properties from caffeine, which leaves contain at levels between 1% and 6% of dry weight. Theobromine and theophylline are two compounds similar to caffeine, and these three methylxanthines contribute to the bitter taste in tea. The caffeine content in a cup of tea ranges between 20 to 70mg per 170ml from around 2.5g of tea leaves, but strongly depends on infusion time and the type of tea. A cup of coffee, in comparison, has 40–155mg of caffeine per 170ml. about 1.5% But caffeine is not the only psychoactive compound in tea – the amino acid theanine comprises about 1% of tea’s dry weight. What is unique to tea, says Nigel Melican, managing director of tea consultancy firm Teacraft, is that caffeine and theanine together have the ‘synergistic and balancing effect of stimulating and relaxing’. Where caffeine stimulates and wards off drowsiness, theanine induces a relaxed alertness that reduces mental anxiety and creates a sense of wellbeing by increasing the brain’s production of gamma-amino butyric acid and promoting alpha brainwave activity. ‘This is why theanine balances the excitation caused by caffeine,’ Melican says. The amino acid also improves the taste of tea by offsetting the astringency of some brews, he adds.