making the hole, watering it, guiding the plant in — all in one motion. Tobacco is cultivated annually, and can be harvested in several ways. In the oldest method, still used today, the entire plant is harvested at once by cutting off the stalk at the ground with a tobacco knife; it is then speared onto sticks, four to six plants a stick, and hung in a curing barn. In the 19th century, bright tobacco began to be harvested by pulling individual leaves off the stalk as they ripened. The leaves ripen from the ground upwards, so a field of tobacco harvested in this manner entails the serial harvest of a number of "primings", beginning with the volado leaves near the ground, working to the seco leaves in the middle of the plant, and finishing with the potent ligero leaves at the top. Before harvesting, the crop must be topped when the pink flowers develop. Topping always refers to the removal of the tobacco flower before the leaves are systematically harvested. As the industrial revolution took hold, the harvesting wagons which were used to transport leaves were equipped with man-powered stringers, an apparatus that used twine to attach leaves to a pole. In modern times, large fields are harvested mechanically, although topping the flower and in some cases the plucking of immature leaves is still done by hand. In the U.S., North Carolina and Kentucky are the leaders in tobacco production, followed by Tennessee, Virginia, Georgia, South Carolina and Pennsylvania. Curing Curing and subsequent aging allow for the slow oxidation and degradation of carotenoids in tobacco leaf. This produces certain compounds in the tobacco leaves and gives a sweet hay, tea, rose oil, or fruity aromatic flavor that contributes to the "smoothness" of the smoke. Starch is converted to sugar, which glycates protein, which is oxidized into advanced glycation endproducts (AGEs), a caramelization process that also adds flavor. Inhalation of these AGEs in tobacco smoke contributes to atherosclerosis and cancer. Levels of AGEs are dependent on the curing method used. Tobacco can be cured through several methods, including: Air-cured tobacco is hung in well-ventilated barns and allowed to dry over a period of four to eight weeks. Air-cured tobacco is low in sugar, which gives the tobacco smoke a light, mild flavor, and high in nicotine. Cigar and burley tobaccos are 'dark' air-cured. Fire-cured tobacco is hung in large barns