Calcium and Magnesium’s effect on mash pH

I have evaluated the effect of calcium and magnesium on the mash pH before when I investigated the pH effects of various waters (The effect of brewing water and grist composition on the pH of the mash). This time I repeated these experiments but didn’t add the calcium and magnesium salts before dough-in but after dough-in. I was wondering if there is a difference or if I could repeat my observations.

The experiment set-up was fairly simple. 7 glasses were filled with 160 ml distilled water and heated in a ~75C water bath. 7 40 g samples of Rahr 2-row were weighed and milled separately with a ~0.75 mm mill gap resulting in a mash thickness of 4 l/kg. Strong calcium chloride and Magnesium sulfate solutions were prepared. The mash samples were doughed-in 3 min apart from each other. Each of the mashes had an initial mash pH of 63-64 C. 5 min after dough in different amounts of either the calcium brine or the magnesium brine were added. One mash remained unchanged. 15 min after the salt addition a sample of the mash was removed, cooled and its pH was recorded. Another sample was taken 60 min after the salt addition.

The results, along with data from previous mash experiments, are plotted in the chart below:

The first observation is that the distilled water pH for the Rahr 2-row is surprisingly low for a pale malt. I also observed this when I used this malt before. The earlieexperiment used pilsner malt which had a more typical distilled water mash pH of 5.7 and 5.8 respectively. Another observation is that magnesium is less effective than calcium in lowering the mash pH. A fact that is already known from the residual alkalinity equation where magnesium hardness is seen as half as effective in neutralizing alkalinity compared to calcium hardness.

As the calcium content increases the achieved pH drop gets smaller which suggests that the curve is approaching a saturation. However, this matters little to practical brewing since the amounts of calcium needed to drop the pH that low by far exceed the recommended amounts. At 42 mEq/kg, for example, the calcium content of the water in a 4 l/kg mash is already 212 mg/l. 50-150 mg/l is the recommended range for brewing water. In case of magnesium 40 mEq/kg mean ~110 mg/l magnesium in the mash water. This is way more than the magnesium levels commonly found in brewing water. Since magnesium is not as effective as calcium anyway it would not be a good choice for lowering the mash pH anyway. If the salts are only added to the mash water, their “flavor active” concentration can be spread over the total water volume used to brew that beer which will reduce the overall impact.

To put this in perspective ~2.1 g of gypsum (calcium sulfate) needs to be added for every kg of malt in order to drop the mash pH by 0.1 units. If we assume that for the average 12 Plato beer ~7.5 l water are needed for every kg of malt, this gypsum addition is equivalent to a water calcium increase by 65 mg/l and a sulfate increase of 155 mg/l.

For calcium chloride only 1.8 g are needed. The calcium content gets bumped by 65 mg/l (when spread over all the water even though the calcium is only added to the mash) and the chloride content gets bumped by 115 mg/l.

There is little change in between the 15 min and the 60 min pH measurement.

2 thoughts on “Calcium and Magnesium’s effect on mash pH

  1. Do you think 1.8g CaCl per kg of malt to lower pH by 0.1 units is true for this Rahr 2-row malt only, or would you expect it to be generally true for all lightly kilned malts? Or all malts?

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