**2. Wine acidity**

Types of acidity in wine: wine acidity is due to the organic acids from grapes, mainly tartaric, malic, and citric acids. There are also other acids that are formed during alcoholic and malolactic fermentations (e.g., acetic, fumaric, succinic, and lactic acids) [1]. Among the grape acids, the most stable and with higher repercussion in pH is the tartaric acid. Malic acid is metabolized by lactic acid bacteria (LAB) during malolactic fermentation (MLF), and its influence in pH is not too relevant. Moreover, potassium contents in soil affect the levels of tartaric acid in grape and must, forming potassium tartrates that are highly insoluble, especially in a polar condition. The precipitation of these salts, especially when ethanol level increases during the alcoholic fermentation, produces the reduction of tartaric acid contents with a subsequent pH augmentation.

Harvesting time is another strongly influential parameter; the sooner the grape is harvested, the higher the acidity. However, acidity decreases significantly when the collection is retarded beyond the normal harvesting conditions because the enologist looks out for the optimum skin phenolic ripeness and also a good seed maturity especially in red varieties. Some alternatives have been proposed to keep acidity using non-matured grapes; one interesting proposal is the use of unripe bunches coming from cluster thinning. These grapes are pressed obtaining a highacidity must which later is cleaned of astringency and excessive vegetal taints by using adsorbents, such as activated charcoal or other products. The juice is mixed with the matured and well-balanced grape to both reduce the pH and improve the acidity [2].
