Chalk None Up For Chalk
It is less common, but some water supplies have LESS alkalinity than needed for brewing beer styles with a lot of crystal and/or roast malts. The popularity of RO water use in brewing has increased the number of brewers that need to increase the alkalinity of their mashing water for some brews. Brewers have tried using chalk to add alkalinity to their mashing water in the past. This discussion will present why chalk is not a good resource for brewing.
Chalk will dissolve (eventually) and contribute its alkalinity. However, the problem is that it is a very time-dependent dissolution...and its time scale is FAR longer than we have in the typical mash. Dissolution is on the order of hours to days and a mash is only about an hour long. So chalk does not end up contributing much alkalinity for a mash.
Kai Troester presented some excellent work on pH in brewing in his 2009 paper posted on Braukaiser.com. Reviewing that paper, you will find that his data shows that chalk does increase mash pH by about 0.1 to 0.2 units. That effect quickly plateaus and adding even more chalk will not increase the mash pH. This response suggests that there is a small quantity of strong acids in the mash that will quickly dissolve chalk, but the phytic acid created from malt is not strong enough to quickly dissolve and react with the chalk. So, chalk is not a good fit for brewing.
There are numerous cases in which brewers have used chalk and found that they could not effectively increase their low mash pH. There is also a hypothesis that chalk can only deliver half of its calculated alkalinity when it has not been fully dissolved into water. While assuming that half-strength response helps, it does not correctly or fully describe the alkalinity contribution of chalk. The plateauing pH response cannot be modeled properly with the half-strength response.
Bru'n Water users should note that chalk is assumed to be FULLY-DISSOLVED in water prior to use in brewing and 100% of its alkalinity is delivered to the mash. To get chalk into solution, it takes time and CO2. If that sounds like a PITA, it is. For that reason, I recommend that brewers utilize other minerals like pickling lime or baking soda when their mash requires more alkalinity.
Forget chalk!