There are primarily two types of fermentation, natural fermentation and forced fermentation, with the duration of the process ranging from two days to two months or more. Natural fermentation, sometimes known as aging, is a chemical reaction caused by moisture and warm temperatures; it occurs when tobacco is packaged in bales or hogsheads. Natural fermentation generally gives tobacco a more uniform color and a milder taste. Forced fermentation involves placing tobacco in huge stacks so that the chemical reaction caused by the moisture and warm temperatures is intensified by the pressure the tobacco is under. Forced fermentation generally gives tobacco a more uniform color, as well as a smoother aroma and taste.