How important is Mg in my brewing water?

My (limited!) understanding of magnesium in the brewing process is that Mg is required for certain yeast enzymes to function efficiently, and that 10-20 ppm is a good target for my water.

My water report gives me 1 ppm Mg, so I've been adding a few grams of MgSO4 to bring my brewing water up to 10 ppm. This obviously ups my SO4 from about 18 ppm to 55 ppm. I'd like to have the ability to keep the sulfates as low as possible, so my question is whether I can skip the MgSO4 addition or if the Mg contribution is more important than keeping the sulfate level down.

Thanks for the input!

Malt generally contains sufficient magnesium to keep yeast happy so I'd say just don't worry about it. Skip the epsom salts and you should be fine.

ajdelange said:

Malt generally contains sufficient magnesium to keep yeast happy so I'd say just don't worry about it. Skip the epsom salts and you should be fine.

Click to expand...

AJ, can you (or anyone else) expand on this assertion? The conventional wisdom on water adjustment is that you want at least 10ppm of Mg; I have to infer from this that there isn't enough (generally) in the malt alone. Is that not true?

So, is there any bare minimum amount of Mg or Ca you need in your water for optimal yeast performance?

Thanks,

TD

According to Briggs in Malts and Malting malt is typically .13% magnesium. So if you put 454 grams (a pound) of malt in 3.78 L (a gallon) of water you would have 454*(.13/100)/3.78 = 0.156 grams per liter of liquor i.e. about 150 mg. Not all of this would be available nor is 0.13% the exact content of all malts but it's clear that it's plenty relative to a 10 ppm requirement.

As anecdotal evidence I offer that I brew with almost completely magnesium free water and my ferments are fine. That's not to say that you can't add a bit of magnesium to low Mg water if you want to. Magnesium does not generally have positive flavor effects (bitter) and as the common salt is the sulfate that means additional sulfate as well. To add 10 mg/L Mg++ you'd also add 42.3 mg/L sulfate if you use epsom salts. That's way more sulfate than I want in my beers (but other brewers like lots more).

AJ, thanks for the clarification.