Sweet corn (Zea mays var. rugosa), also called sweetcorn, sugar corn, or simply corn, is a variety of maize with a high sugar content. Sweet corn is the result of a naturally-occurring recessive mutation in the genes which control conversion of sugar to starch inside the endosperm of the corn kernel. Unlike field corn varieties, which are harvested when the kernels are dry and fully mature, sweet corn is picked when immature and eaten as a vegetable, rather than a grain. Since the process of maturation involves converting sugar into starch, sweet corn stores poorly and must be eaten, canned, or frozen before the kernels become tough and starchy.