Why Ca and Mg Are Not Substitutes For Acid in Sparging Water

An interesting question came up recently. "Why can't we consider the acidifying effect of calcium and magnesium salts in the sparging water when we calculate its acid dose?"

As you should know, calcium and magnesium ions react with phytin compounds from malt to help acidify the mash and reduce its pH. In addition, we know that sparging water should have low alkalinity to reduce the possibility of tannin and silicate extraction during sparging. So it could make sense that we should include the acidifying effect of calcium and magnesium when figuring out how much acid we need to neutralize water alkalinity.

However there is an important factor to recognize from the sparging process: that is that the amount of phytins is substantially reduced during the sparging process and that acidifying effect is also reduced. For brewers that continuously (or 'fly') sparge their grist, the amount of phytins in the mash fall to near zero and that acidifying effect disappears at the end of the runoff. That is precisely the time when the mash needs low alkalinity sparging water to avoid tannin and silicate extraction and those calcium and magnesium ions would not produce an acidifying effect. So, we do need to calculate our sparging water acidification without considering the benefit of the water's calcium and magnesium content.

Batch spargers should also follow this approach since a significant quantity of the mash phytins will have been drained away with the initial wort runoff and there may not be enough phytin left to create the acidification effect in the subsequent mashing water addition.

In brewing, acid is your friend. Enjoy!