The nitrogenous compounds of must and wine are derived from grapes and can be augmented with yeast nutrients. They play important roles in fermentation, clarification, and potential microbial instability of wines.
The amount of ammonium ions in must influences the rapidity of fermentation start and evolution. The ammonia concentration ranges are from 24 to 209 mg/L (ppm) in grapes and from a few mg/L (ppm) to about 50 mg/L (ppm) in wine.
The content of ammonium ions will drastically decrease during the alcoholic fermentation, then increase again, especially in red wines, at the end of the malolactic fermentation becuase the lactic bacteria release ammonia nitrogen into the wine.
The pH of wine is important to determine because it will affect the quality of the product in terms of taste, color, oxidation, chemical stability and other factors. The general rule of pH in winemaking is the higher the pH reading, the lower amount of acidity in the wine. Three important factors in determining the pH of wine include the ratio of malic acid to tartaric acid, the amount of potassium and the total amount of acid present.