All tea, no matter the type, comes from the Camellia sinensis plant. How the tea differs is from how it is processed.
Black teas undergo the longest processing of any other tea. Once the leaves are harvested, they are left out in the sun to slightly wilt. The leaves are then rolled to break open, which causes them to ferment. As the leaves ferment, they turn from green to black. After the leaves reach their optimal color, they are then dried and packaged.
Black teas can be divided into 3 different categories based on where they are grown and harvested. Assam teas are grown in the Assam Valley of India, Darjeeling is grown in the Darjeeling Province of India, Ceylon teas are from Sri Lanka, and China Blacks are from, well, you can probably deduce that one.
Green tea does not undergo fermentation. After the leaves are harvested, they are either steamed or pan fired. The leaves are then rolled into different shapes and then laid out for drying. The different shapes produced the different types of green tea. For example, sencha tea is rolled into fine strands, and gunpowder tea leaves are rolled into pellets. After the green tea leaves are shaped and dried, they’re ready for packaging.
Oolong tea is wilted like black tea, but instead of letting it ferment like black teas, the tea leaves are fired immediately after wilting to prevent additional fermentation. How long the leaves are allowed to wilt and ferment depends on the desired color. As a result, oolong tea can range from dark green to almost black.
White tea has the least amount of processing. These tea leaves are picked early in the year when the buds are still closed and the tiny white hairs are still visible on the leaves. The top leaves and buds are the only parts gathered at harvest. The leaves are then dried in the sun, but they are not steamed or pan fired after drying.