Making black tea is more complex and time consuming. The freshly plucked leaves are brought to the tea factory, which is most often located on the estate, or very near to a collection of small farms. Once it arrives, the tea is laid out on screens fitted to long wooden boxes call withering troughs. Here the tea is allowed to wither. This process allows air passing through and over the intact leaves begins to remove moisture. The withered tea reduced to about 60% moisture content, is then rolled. This rolling disrupts the cellular structure of the tea leaves, releasing enzymes present in the leaf that will combine with polyphenols and other constituents in the leaf to form the unique molecular structures which gives black tea its distinctive flavor and aroma. The leaves are now moved on to the fermentation stage. Fermentation is actually the oxidation of the tea constituents. Chemical interaction between the various components of the tea leaf in the presence of oxygen will cause the tea to turn from green to coppery red to deep brown and, finally, a near black color. After fermentation, the tea is dried, or fired, using air that has been heated to between 210 to 250 degrees Fahrenheit. The moisture content is reduced to around 3%.