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
Quinta classification of Port vineyards in the Douro the permitted production level of the vineyard and what price the grower can receive for the wine they produce from the grapes. Quintas are given numerical ratings in several categories – age of the vines, altitude, aspect, vine density, gradient, granite content of the soil, schist content of the soil, types of grape varieties planted, overall location of the vineyard, microclimate, mixture, vineyard soil type, vine productivity, and vineyard maintenance. Vineyards that have favorable attributes in a particular category (such as being planted with an optimal low density of vines) are award points while negative attribute (such as having too