Magnesium in Brewing Water

An old brewer's adage warns brewers to NEVER add magnesium to their brewing liquor. In some respects, this can be taken as truth since brewing malt adds significant magnesium content to the wort and it is sufficient for yeast health. However, there are cases where the brewer may want to increase the magnesium content of the brewing water for flavor.

One note on adding magnesium to your brewing water. It is critically important that you know what the starting magnesium content of the water supply is before adding additional magnesium. The story below is a case in point.

While I was assisting with the Water book, co-author Colin Kaminski commented that he often adds magnesium to his brewing liquor for hoppy beers. In talking with his fellow professional brewers, some warned that they had tried adding magnesium and it totally ruined their beers. With a bit more investigation, Colin found that their water already had high magnesium content and there was no need to add more. The recommended upper limit for magnesium in brewing water is around 40 ppm and above that the beer flavor is severely affected. Apparently those brewers had exceeded that level with their magnesium additions.

I recommend staying well below that 40 ppm limit for magnesium to avoid problems with beer flavor. There are virtually no waters from historic brewing cities that have magnesium that high. Only Burton water can be found at that level and it is typically diluted to reduce the level somewhat. I suggest that around 20 ppm magnesium may be a safe level to add to brewing water in order to enhance the perceptions of bitterness in the beer. While that would be counterproductive in a malt focused beer, it could be welcome in a bitter or hoppy beer.

If you are having difficulty achieving the bitter edge you want in your beers, possibly boosting the magnesium concentration in your brewing water will be something you should try. Enjoy!