The bloom on the skin of most grapes and apples is yeast; there is no need to add extra yeast. For cheap and easy cider, crushed apples were not pressed; they were simply mixed with water and fermented. However, apple pomace is commonly exposed to the air for 12 hours to increase the sugar content. If so, the cider should be pasteurized to kill vinegar bacteria, and yeast must then be added. Also, adding a little malt breaks apart the pectin in fruit and changes starch to sugar in grain and potatoes; fermentation is faster, and the alcohol content is higher.