Mash pH is the result of the balance between acidity of the grist and alkalinity of the water. The acidity of the grist is determines by the malts used and darker malts are generally more acidic than lighter colored ones. The color of the malts used in the grist also determine the beer color to a large extend. On the other hand, the water alkalinity, to be correct its residual alkalinity, is determined by its mineral composition. It therefore stands to reason that beer color and water composition, necessary for a proper mash pH, are related.
This article uses results from mash pH experiments to shed light on the relationship between beer color, mash pH and water composition. It also develops a formula that can be used to make a crude prediction of the mash pH or the alkalinity necessary for a given mash pH based on the color and mash thickness of the beer.
Malt color, type and acidity
Brewers know that darker malts are more acidic. But what does it mean for a malt to be more acidic? They for sure don't taste sour.
Malt acidity is the ability to lower the mash pH and it can be measured via 2 means. One is the pH of a distilled water mash. Because of the absence of pH affecting ions the pH of that mash is determined only by the malt acidity and the mash thickness. Another approach is to take a sample from such a mash and add a strong base (e.g sodium hydroxide) to it until a predetermined pH (e.g pH 5.7) is reached. The amount of base added per unit of malt is a direct measure of that malts acidity. Testing the distilled water mash pH works well for base malts. Specialty malts, however, are generally much more acidic than base malts and testing their acidity through titration works better.