The simplest, oldest, and slowest method was perfected in the Middle Ages in the French city of Orléans, where spoiled barrels of Bordeaux and Burgundy wine on their way to Paris were identified and salvaged as vinegar. In the Orléans process, wood barrels are partly filled with diluted wine, inoculated with a mother from a previous batch, and allowed to ferment. Periodically, some vinegar is drawn off and replaced by new wine. This method is slow, because the transformation of alcohol to acetic acid is limited to the wine surface exposed to the air. But the slow fermentation leaves time for reactions among the alcohol, acetic acid, and other molecules, and produces the finest flavor. When optimized, this process can yield a barrel full of vinegar in two months.