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
History of the wine press Terentius Varro, Pliny the Elder and others described wooden wine presses that utilized large beams, capstans and windlasses to exert pressure on the pomace. The wines produced by these presses were usually darker, with more color extracted from the skins but could also be more harsh with bitter tannins also extracted. That style of wine press would eventually evolve into the basket press used in the Middle Ages by wine estates of the nobility and Catholic Church leading to the modern tank batch and continuous presses used in wineries today. The exact origins of winemaking (and, thus, of pressing grapes)