The four types of true tea – black, green, white, and oolong – are all made from the leaves of the evergreen shrub Camellia sinensis, but the differences between them are due to the ways in which they’re processed into individual varieties.
White tea is the least processed and is made from buds and certain leaves of the Camellia sinensis plant, which are steamed and dried. Because it is made from the bud of the plant, it is naturally caffeine free.
Green tea is produced from freshly harvested leaves, which immediately are steamed to prevent oxidation or oxygen exposure. Both white and green teas are particularly high in polyphenols. Green tea is slightly caffeinated – and has been used by monks for generations as a tool to support hours of meditation, by promoting a clear and present mind.
Oolong tea is allowed to oxidize for a short period, and black tea is completely oxidized. The more oxidized the tea, the higher the caffeine level.
And last, Pu-erh tea (pronounced POO-air) is the most oxidized form of tea, often aged, and sometimes very expensive. Unlike other teas, which get stale over time, pu-erh can mellow and improve with age like fine wine. Some pu-erh teas are more than 50 years old, and rare ones sell for many thousands of dollars in Asian specialty stores.
In America, we tend to call anything that infuses boiling water and isn’t coffee – tea. In the rest of the world, an infusion that doesn’t include a part of the Camellia sinensis shrub is called a tisane, or herbal blend.