In a recent episode of Today I Found Out, host Simon Whistler explains the difference between black tea and green tea, what the two teas have in common and the history of both.
The difference between these teas is achieved via different processing methods. Manufacturers create green tea by picking the leaves off the plant and then heating them immediately afterwards. This is commonly done by pan firing the leaves or steaming them. Sufficient heat stops the leaves from oxidizing, allowing them to maintain their green color.