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 chalk


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 dissolved.


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 A 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 differences


Conclusion:

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