Beer color, alkalinity and mash pH

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Mash pH is the result of the balance between acidity of the grist and alkalinity of the water. The acidity of the grist is determined 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. This formula has been implemented in the water calculator (Kaiser_water_calculator.xls) to predict the mash pH from beer color, mash thickness and water composition.

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.

In aforementioned mash pH experiments the following formula was developed for calculating the distilled water pH of a given grist.

Formula pH distilled water mash.gif

Where: pHDI water mash: the mash pH of the grist in distilled water pHbi: the distilled water mash pH that particular base malt i gbi: the contribution of base malt i to the weight of the grist (between 0 and 1) gsj: the contribution of the specialty malt j to the weight of the grist (between 0 and 1) asj: the acidity of the specialty malt j in mEq/kg Rmash: the mash thickness in l/kg

Along with the measured values for the distilled water pH of select base malts and acidity select select specialty malts 210 recipes were simulated. The recipes were thrown together randomly with the following constraints:

Beer color to DI pH.gif
SRM to DI pH for different mash thickness.gif