Determining the pH of wine during fermentation is an operation of fundamental importance: the pH affects the organoleptic characteristics of the wine (starting with the aroma), and provides an indication of the degree of ripeness of the grapes, the colour the liquid will have, the microbial and chemical composition of the must and the wine itself. Only by taking this measurement can the development of superfluous microorganisms be prevented, and the effectiveness of sulphur dioxide (used as a preservative) and the efficiency of the conversion from malic acid to lactic acid by the action of the yeast be increased.In fact, it is the acids that determine the freshness a wine offers on tasting: fixed acids (tartaric acid, malic acid, lactic acid and their salts) balance the warmth and softness of the alcohol and sugars, conveying a sensation of freshness of taste. And they thus make it possible to distinguish between flat wines (weakly acidic), fairly fresh wines and acidic wines (very acidic).