The Major Types of Tea: It’s All About Oxidation

As I explained before, black, green, and every other kind of tea are all made from the same plant. The devil’s in the details of course, but broadly speaking, the principle difference between them is how much the tea leaves are allowed to oxidize—a.k.a. brown—after they’re picked but before they’re dried, which shuts down the enzymatic process. The less a tea is oxidized, the more it tastes like the leaf itself: crisp, fresh, and green. The more it’s oxidized, the more it develops rich, dark, and malty notes that, done right, complement the leaf’s natural flavors.

via Beyond English Breakfast: An Introduction to the World's Great Teas | Serious Eats.