pH and Acidity

The pH and acidity are very important characteristics of wine, but the beginner may not be equipped to measure them.

The pH is the concentration of positive hydrogen ions in solution. The more H+ ions, the more acid the solution. The pH scale goes from 1 to 14, where 7 is neutral, above 7 is basic and below 7 is acidic. The pH of juice for wines should be between 3.2 and 3.5. pH is difficult to change and it is best if you begin with a juice with a pH in the desired range. pH is important in maintaining microbial stability, so the wine doesn’t spoil. pH is measured on a meter at room temperature or at the temperature specified on the equipment. The pH meter must be calibrated using buffer solutions of pH 4 and pH 7 (or as specified by the manufacturer).

The acidity level is the amount of tartaric, malic, lactic and citric acids in the wine. Acidity is expressed as grams per liter of tartaric acid since tartaric is the major acid in wine. Juice for wine should have acid levels between 0.6 - 0.9 grams/100 ml tartaric (0.6 - 0.9% Total Acidity). Acidity is important since it balances sweetness in the wine. A wine will be flat with too low an acid level or sour with too high an acid level. Acidity in wines is measured by performing an acid-base titration. A known amount of juice is diluted in distilled water and a known concentration of base (sodium hydroxide) is used to titrate (measured amounts mixed into the sample at intervals) to an end point, shown by a phenolphthalein indicator or a pH meter. Once the endpoint is reached, the amount of base used to reach the endpoint can be inserted into a formula that will calculate the amount of acid based on tartaric acid.  See determination of total acidity.