Magnesium Sulfate

[Jimmy]

I've noticed some comments online suggesting to be careful with Magnesium Sulfate (Epsom Salt) when brewing. I'm going to be using RO water for my first brew and when calculating my water treatments it's suggesting I add 13g of magnesium sulfate to my water for 22.9ppm magnesium. Should I be concerned with this/does it seem like a lot, or should I only be concerned if the ppm starts creeping higher?

[GuingesRock]

Good water link here: https://sites.google.com/site/brunwater/water-knowledge" onclick="window.open(this.href);return false;

Magnesium is typically the secondary ion creating hardness in water. It accentuates flavor with a sour bitterness when present at low concentration, but it is astringent at high concentration. Magnesium is a yeast nutrient and an important co-factor for certain enzymes. Like calcium, magnesium reacts with the malt to lower the mash pH, but with a reduced effect compared to calcium. The preferred range for magnesium concentration is 0 to 30 ppm. Exceeding 40 ppm is not recommended. A minimum of 5 ppm magnesium is known to be desirable for good yeast flocculation. A typical barley or wheat mash grist will contribute more than 5 ppm magnesium to the wort for proper yeast flocculation so it is not necessary to add magnesium to brewing water unless it is desired for its flavor effects. Increasing the magnesium content of mash water is not a useful tool for reducing the pH of the mash water since the allowable concentration range for this ion is small.

[CiderBeerWine]

ppm is the same as miligram per litre (mg/L).

So

22.9mg/L x (1L) =22.9mg (assume you have 1 litre of water)

22.9mg x (1g/1000mg) = 0.0229g

That is how many grams of Mg you'd need in the water, but you have MgSO4 so you need to account for the weight of the SO4 so you need to find the moles of Mg in 0.0229g, and then find the mass of MgSO4 this corresponds to noticing each MgSO4 has 1 Mg in it so it is a 1:1 ratio

So

0.0229g / (24.3g/mol) = 0.000942 moles of Mg, and it is a 1:1 ratio so also 0.000942 mol of MgSO4

So the mass of 0.000942 mol of MgSO4 is:

0.000942mol x (120.366g/mol) = 0.113 g

So for every litre of water you need 0.113 g of MgSO4

[CiderBeerWine]

For a 23 L batch that would be

0.113g/L x (23L) = 2.6 g of MgSO4

[kberry]

epsom salt is heptahydrate - MgSO4-7H2O

all the math you did was correct up until the end, so:

0.000942 mol x (246.47 g/mol) = 0.232 g for every litre

0.232 g/L x 23L = 5.34 g of epsom salt (MgSO4-7H2O)

[CiderBeerWine]

Whoops, I didn't know the epsom salts were hydrates, although its very hydroscopic so that makes sense.