Undissolved vs. dissolved chalk in the brewing water

This was the first time that I compared
dissolved chalk against undissolved chalk in a 5-gal “production”
batch of beer. Up to this point I have only done small scale
experiments. Those experiments suggested that chalk dissolved with
CO2 would be twice as potent in raising the mash pH as undissolved
chalk is. As a result I new that I should cut the amount of chalk
needed in half when it will be dissolved with CO2.

To brew the Schwarzbier I used the
following grist. This is my standard recipe for a Schwarzbier:

  • 53% Pilsner malt

  • 40% Munich Type II malt

  • 4% CaraMunich III malt

  • 3% Carafa I special

The water was prepared from reverse
osmosis water by adding the following salts. Version A uses
undissolved (i.e. suspended chalk) while version B used dissolved

salt beer A beer B
Table salt (NaCl) 25 ppm 25 ppm
Epsom salt (MgSO4*7H2O) 40 ppm 40 ppm
Magnesium chloride (MgCl2*6H2O) 50 ppm 50 ppm
Baking soda (NaHCO3) 40 ppm 40 ppm
Chalk (CaCO3) 200 ppm 100 ppm

The resulting profile was calculated as
follows. Note that I do have an old analysis of the reverse osmosis
water which I included in the calculated mineral profile:

ion beer A beer B
calcium 85 ppm *) 45 ppm
magnesium 11 ppm 11 ppm
sodium 26 ppm 26 ppm
sulfate 17 ppm 17 ppm
chloride 38 ppm 38 ppm
alkalinity as CaCO3 144 ppm 144 ppm
residual alkalinity as CaCO3 77 ppm 105 ppm
residual alkalinity in dH 4.3 5.9

*) There is some ambiguity as to how
much calcium is actually contributed by undissololved chalk since it
contributes only half its alkalinity potential, it may also
contribute only half its calcium. These results assume that the chalk
contributed all its calcium. The result is a lower residual
alkalinity compared to the water with only half the chalk but

The salts were then weighed. For beer
A, they were mixed into the strike and sparge water. Since the chalk
was not dissolved the water remained cloudy. Water treatment for the
strike water was done in the mash kettle.

For beer B the salts were added to 2
liter soda bottles and reverse osmosis water was added. Then the
bottles were carbonated with a carbonator cap. Once sufficiently
carbonated the water cleared overnight which was a sign that the
chalk got dissolved. This water was then added to the remaining
reverse osmosis water for mashing and sparging. The mash water was
prepared the night before to allow residual CO2 to escape. No chalk
precipitated during that time, There was also no precipitation of
chalk during the heating of the strike water or the sparge water.

The resulting pH values during the
brewing process are shown in the following table. All pH values were
measured with a sample cooled or heated to 25 C

process step beer A beer B
initial mash pH (63 C) 5.6 5.68
dextrinization rest (72 C) 5.51 5.61
mash out (76 C) 5.5 5.54
kettle full (pre-boil) 5.62 5.62
cast out wort (post boil) 5.66 5.56
after 7 days of fermentation 4.41 4.45

For both beers the pH dropped during
mashing which I contribute to the continued release of acidic
compounds from the dark specialty malts. One oddity is that for batch
A, which used undissolved chalk, the kettle full pH is lower than the
cast out pH. Generally the pH falls during boiling. This is something
worth paying attention to in future batches although it may also have
been a measurement error. The initial mash pH of batch B is greater,
which supports the fact that the residual alkalinity of its water
should have been higher. This is the case if all the calcium added by
the chalk is considered for undissolved chalk as it was done in the
aforementioned water analysis.

I have not yet done a final tasting
with these two beers. But preliminary tasting of both batches during
their fermentation and conditioning did not show any significant


To achieve roughly the same mash pH,
only half the chalk is needed when it is dissolved with CO2.