Black teas are the most processed among the varieties. Freshly plucked leaves are withered, and are then rolled in order to lightly bruise the leaves, encouraging them to release their juices. The leaves are then laid out in a cool, humid room to absorb oxygen. The leaf color changes from green to a coppery red, giving black tea its distinctive liquor. The fermentation is then stopped, and the leaves are heat fired and dried. Black teas generally have the most caffeine.
Oolong teas are semi-oxidized before being rolled and dried. Oolongs can be deeply or lightly oxidized, resulting in some oolongs that are either very green or closer to a black tea. Oolongs are prized for their complex, floral and fruity characteristics. Moderate caffeine.
Green teas are usually minimally oxidized, if at all, being pan fired or steamed and dried after shaping the leaves. Fresh green tea might taste slightly sweet, vegetal, nutty, and/or grassy, but shouldn't be bitter if prepared properly. Moderate caffeine.
White teas are the least processed of all. Only the youngest leaves and buds are picked, still covered with down, and are air dried and steamed. White tea produces a fragrant, sweet tasting brew. Light caffeine.
Rooibos grows in the Cedarburg Mountain region of South Africa, and is often referred to as "red bush tea." Rooibos is naturally caffeine-free, and has recently become quite popular due to its fruity, sweet flavor and antioxidant content.
Herbal teas are any beverage infused with plant material that does not include the Camellia sinensis plant; this opens doors for wide varieties of teas that can be both medicinal and delicious. Herbal beverages are often referred to as "tisanes" or "infusions", and are generally caffeine free.