In India, palm wine or toddy is served as either "neera" or "pathaneer" (a sweet, non-alcoholic beverage derived from fresh sap) or "kallu" (a sour beverage made from fermented sap, but not as strong as wine). Palm sap contains natural yeasts, which perform the fermentation of glucose to alcohol, as well as acetobacter, which subsequently converts the alcohol to acetic acid (vinegar). Optimal consumption time is one day after tapping when the vinegar content is minimal; beyond this time, it becomes increasingly sour. Some palm wine drinkers prefer their beverage more sour than usual, but fermenting for too long will result in vinegar rather than wine. Refrigeration extends beverage life, as do a variety of spices, which also contribute flavor.