Living tobacco leaf contains several enzymes that continue to function after the leaf has dried and died. These oxidize carbohydrates and proteins and are a primary cause of what we identify as aging in finished tobacco. The speed at which these chemical changes occur is dependent on temperature and the presence of moisture. Many different methods can be used to increase the speed of this process, though it still may require as long as several years to run to near completion. This is why an “aged” leaf usually seems “better” than a leaf with less age. Basic tobacco fermentation-aging does not depend on the action of microbes, though they may influence subtle characteristics late in the aging process.