Acids in wine ripened grapes. While concentration varies among grape varieties, it is usually found in higher levels with red wine grapes. The acid is created as a byproduct of the metabolization of nitrogen by yeast cells during fermentation. The combination of succinic acid with one molecule of ethanol will create the ester mono-ethyl succinate responsible for a mild, fruit aroma in wines. Acidity is highest in wine grapes just before the start of "veraison", which ushers in the ripening period of the annual cycle of grape vines. As the grapes ripen, their sugar levels increase and their acidity levels decrease. Through the
Late harvest wine Late harvest wine Late harvest wine is wine made from grapes left on the vine longer than usual. "Late harvest" is usually an indication of a sweet dessert wine, such as late harvest Riesling. Late harvest grapes are often more similar to raisins, but have been naturally dehydrated while on the vine. Botrytis cinerea, or "noble rot", is a mold that causes grapes to lose nearly all of their water content. Wines made from botrytis-affected grapes are generally very sweet. Botrytis cinerea is a fungus that affects many wine grapes and causes them to shrivel into moldy raisins. The fungus