Acids in wine responsible for the sour taste of vinegar. During fermentation, activity by yeast cells naturally produces a small amount of acetic acid. If the wine is exposed to oxygen, "Acetobacter" bacteria will convert the ethanol into acetic acid. This process is known as the “acetification” of wine and is the primary process behind wine degradation into vinegar. An excessive amount of acetic acid is also considered a wine fault. A taster's sensitivity to acetic acid will vary, but most people can detect excessive amounts at around 600 mg/l. Ascorbic acid, also known as vitamin C, is found in young wine grapes
French wine spreading Christianity and planting vineyards. During the Middle Ages, monks maintained vineyards and, more importantly, conserved wine-making knowledge and skills during that often turbulent period. Monasteries had the resources, security, and motivation to produce a steady supply of wine both for celebrating mass and generating income. During this time, the best vineyards were owned by the monasteries and their wine was considered to be superior. Over time the nobility developed extensive vineyards. However, the French Revolution led to the confiscation of many of the vineyards owned by the Church and others. The advance of the French wine industry stopped abruptly