Black tea
Popular varieties of black tea include Assam, Nepal, Darjeeling, Nilgiri, Turkish, 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). The most common fault when making black tea is to use water at too low a temperature. Since boiling point drops with increasing altitude, it is difficult to brew black tea properly in mountainous areas. Warming the tea pot before steeping is critical at any elevation.
Western black teas are usually brewed for about four minutes and are usually not allowed to steep for less than 30 seconds or more than about five minutes (a process known as brewing or mashing in Britain). 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 should be 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.