Black tea is a "true" tea made from leaves more heavily oxidized than the white, green, and oolong varieties. It is generally stronger in flavor and contains more caffeine than more lightly oxidized teas. Black tea tends to preserve its flavor for several years unlike green tea and therefore blends and mixes well with various plants in order to obtain a variety of flavors.
After the harvest, the leaves are withered by blowing air on them followed by 1 of 2 processes. The CTC (Crush, Tear, Curl) or orthodox method is used for lower quality leaves that end up in tea bags and are processed by machines. This method is efficient and effective for producing a better quality product from medium and lower quality leaves. Orthodox processing is done either by machines or by hand. Hand processing is used for high quality teas. While the methods employed in orthodox processing differ by tea type, this style of processing results in the high quality loose tea sought after by many connoisseurs. Next, the leaves are oxidized under controlled temperature and humidity. This process is also called fermentation, though no fermentation takes place. The level of oxidation determines the quality of the tea. Since oxidation begins at the rolling stage itself, the time between these stages is also a crucial factor in the quality of the tea. The leaves are then dried to arrest the oxidation process, and then finally, the leaves are sorted into grades according to their sizes (whole leaf, brokens, fannings and dust), usually with the use of sieves. The tea could be further sub-graded according to other criteria. After sorting, tea is ready for packaging.