How many types of tea are there? The answer to that question really depends on who you ask. There are many gray areas in tea and there is much left open to interpretation. The western world is also just now discovery categories of tea that have existed in the tea lands for centuries. In this post, I will be listing the categories of tea as I see them.
White tea is the least processed type of tea. Contrary to popular belief and many tea vendor's websites, it is not rare! After picking, the leaves are laid out to dry in the sun. Hot air can also be used to achieve this. There is no "kill green" step and the leaves are not typically shaped in any way. Some withering occurs but it is not necessarily something producers try to achieve (like they might with black tea or oolong). Silver Needle is probably the most well-known white tea but there are other varieties that are made with more than just buds.
Green tea is often referred to as unoxidized but that's not exactly the case. Tea leaves begin to wilt as soon as they are removed from the plant. Heat is applied to the leaves by the tea producer as quickly as possible. This brings oxidation to a halt so as to preserve them in their green state. Chinese teas are typically pan fired whereas Japanese green teas are usually steamed. Some manufacturing methods also use blanching the leaves in hot water.
Black tea undergoes the same processing steps as oolong but the leaves are completely (or very nearly) oxidized. Both the finished leaves and the brewed tea will have a reddish brown coloration. This is caused by catechins being converted into thearubigins. The taste of black can vary quite a bit depending on the region and how the tea is made. Although it's usually thought of as being served with milk and sugar, black tea is not always the punchy and astringent kind.
The category of dark tea, also known as hei cha, refers to any tea that is fermented. It's important to note that fermentation in tea is a different biological process than the one used to produce beer and wine. Puerh falls under this category as do similarly processed teas from regions of China other than Yunnan. Some argue that raw puerh should be categorized as a green tea but there are some key differences. Sheng is heated in a similar fashion but the leaves are dried in the sun rather than by hot air. They retain some of their natural enzymes and bacteria which will allow the tea to gradually oxidize as well as ferment over time.
Please let me know in the comments if you prefer a different method of categorizing tea. I'd love to get some healthy discussion going on this!