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


  • 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

In English the weighted avarega of the distilled water mash pH for all the base malts and the titration point for specialty malts (5.7) is determined. This pH is then lowered by the acidity of the specialty malts. The more acidic they are, the higher their grist percentage and the thicker the mash is the more the lower the mash pH of the grist will be.

Random recipe creation and pH and color calculations

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:

  • 15 recipes mixed only base malts
  • 45 recipes mixed base malts with up to 15% crystal malts. 50 of these recipes used only 2-row as base malt. The other 15 used a random mix of different base malts. The percentage of crystal malts in these grists was randomly chosen between 1 and 15%. In addition to that the types and and percentages of different crystal malts were also chosen randomly
  • 45 recipes mixed base malts with up to 8% crystal malts and up to 8% roasted malts. 50 of these recipes used only 2 row as base malt while the other 15 used a mix of base malts. Similar to the recipes that used only crystal malts as specialty malts these recipes here had their actual crystal and roasted malt percentages determined randomly. The same applied to the types of malts that were chosen
  • 45 recipes used only roasted malts. Those roasted malts recipes were created similar to the crystal only recipes mentioned earlier

Crystal and roasted malts were treated as distinct groups since they also formed distinct clusters when their acidity was plotted over their color.

For all these random recipes the distilled water mash pH of the grist and the color of the beer was calculated. The DI water mash pH was determined for 4 different mash thicknesses 2, 3, 4, and 5 l/kg. For the color calculation it was assumed that the total grist weighed 10 pound and the cast out volume was 5 gallon.

Beer color formulae.gif

The result were 4 sets of 210 data points that represent realistic combinations of beer color (SRM) and the distilled water mash pH of their grists. One set for every evaluated masch thickness (2, 3, 4 and 5 l/kg). The data for 3 l/kg is shown in Figure 1.

Figure 1 - distilled water mash pH over beer color for 210 randomly generated recipes

Based on this chart we can make a few observations:

  • There is no simple curve that can estimate the grist pH from the beer color.
  • a wide range of beer colors can yield an grist pH in the desired pH range and an even larger color range can yield an acceptable mash pH (Note that this does not yet take the residual alkalinity of water into account)
  • "Crystal only" and "Roasted only" recipes cluster form clusters which can be respresented reasonably well with linear functions.
  • The more roasted malt is used to achieve the desired beer color the less pH drop can be expected per unit of color. This stems from the fact that roasted malts have less acidity per unit of color compared to crystal malts
Figure 2 - Grist pH over SRM simulation of 210 different Random recipe for 4 different mash thicknesses

Figure 2 shows how the SRM to pH relationship changes for different water to grist ratios: the grouping remains the same, only the parameter for the linear functions change.

With these observations the idea was born to estimate the grist pH from the color, mash thickness and the percentage of roasted malts in the specialty malt portion of the grist. I.e.if there are no specialty malts the linar function for "cara only" is used and if all specialty malts are roasted malts the linear function of "roasted only" is used. If there is a mix of the two a function that lies berween the two is used.

Using the standard notation of a linear function the pH estimation from beer color and mash thicknes can be written as

Linear mash pH function.gif

Where the new variable are:

  • m(R_mash,p_roasted) - slope of the function which itself is a function of mash thickness and roasted malt percentage
  • b(R_mash,p_roasted) - y-intercept of the function which itself is a function of mash thickness and roasted malt percentage
  • p_roasted - the percentage of roasted malts in the specialty malt portion of the grist (0 - 100%)

As mentioned earlier the slope and y intercept of the linear function are determined by simple interpolation between the slope and y-intercept for "cara only" and "roasted only" recipes:

SRM to RA slope and intercept.gif

Now for some more regression analysis. If the slopes and y-intercepts for "cara only" and "roasted only" recipes are plotted for the 4 different mash thicknesses (Figure 3) it is apperent that they can be fit with a logarithmic regression. The paramaters the were found led to the following formulas:

SRM to RA parameters.gif

These formulas have been implemented in []. It should be noted that the approach outlined here only provides for a crude estimation of the mash pH and that there are cases where this prediction will not be correct. In particular when the distilled water mash pH of the base malts differ significantly from the pH values used in the simulation. Another limitation is the range of mash thicknesses. But it is assumed that the range of 2-5 l/kg should cover most practical mashes.