Originally called cha and tu in China, tea comes from the Camellia sinensis shrub, a perennial evergreen that grows mainly between the tropics of Cancer and Capricorn. (Infusions of roots, flowers, and herbs, such as chamomile and rooibos, are often called herbal teas but are more properly tisanes.) Though some 30 countries grow Camellia sinensis, most tea is produced in India, China, Sri Lanka, Indonesia, and the Kenyan highlands.

The different strains of Camellia sinensis, the geographic microclimate in which they're grown, and the age and the part of the leaf that is picked all yield different types of tea with unique characteristics. The finest teas are hand-plucked, while mass market teas are picked by imprecise machinery, compromising quality. How the leaves are processed and the level of contact with oxygen determines the type-white, green, yellow, oolong, pu-erh, or black, which makes up 87 percent of the tea drunk by Americans.

White tea, from a strain endemic to China's Fujian province, undergoes no oxidation. The leaves are steamed shortly after they're picked to halt the process. When they're left to oxidize longer, the result is green tea. For black tea, oxidizing leaves are piled up in a heated room, which initiates a fermentation process that breaks down the leaf, releases tannins, and changes the color. Bits of broken leaves that result from the processing are allocated to tea bags for their quick diffusion.

The tea leaves might then be flavored - green tea layered with jasmine flowers, for example, or black tea leaves sprayed with bergamot orange oil and, increasingly, dried bergamot fruit to make Earl Grey. Blended teas might contain different tea varieties (English Breakfast traditionally includes Keemun and Assam) or the same kind from different estates. To meet Americans' growing desire for flavored tea blends, companies now use flowers and herbs from around the world.