Black tea comes mainly from India but other countries such as China, Sri Lanka, Africa, and Indonesia also produce black teas. As the most extensively processed tea, black tea is fully fermented or oxidized. The fresh leaves are left out to wither in direct sunlight for approximately twelve hours. Air passing through and over the leaves begins to remove moisture. The withered leaves are then rolled disrupting the cellular structure, and releasing the chemicals essential to the final colour, flavour, and aroma. Rolling can be done by hand or machines that crush the leaf. Mechanized crushing or CTC machines cut, tear, and curl the leaves into small fragments and create broken tea grades. Finally, the tea is fired or dried to arrest the natural decomposition. The dry tea is then sorted into different grades or sizes of leaf.