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
Straw wine scale. Grapes should originate in a single wine sub-region and reach at least 6% of alcohol. De Trafford created the first Vin de Paille to be released under the new appellation "Wine from Naturally Dried Grapes" in 1997. They use 100% Chenin blanc. A number of wineries produce straw wine, known in Spanish as "vino de pasas", including Bodegas Oliveros and Bodegas Gonzalez Palacios. Most involve a blend of two grapes, the first one usually a Muscat. Pedro Ximénez grapes are dried in the sun before being vinified, fortified and matured in a solera system like other sherries. Another straw