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Old 10-04-2011, 06:58 AM   #1
400d's Avatar
Aug 2009
Posts: 583
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ok guys, just a quick question for all you chemists here. I got three different bags of MgSo4 with different labels:

1. Magnesii Sulfas a.
2. Magnesii Sulfas h.
3. Magnesii Sulfas crystal

Since they're all labeled differently I wonder which one is ok for brewing (water adjustments)?

Appreciate your answers. cheers
Brew me a river...

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Old 10-04-2011, 12:45 PM   #2
Aug 2010
McLean/Ogden, Virginia/Quebec
Posts: 9,661
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They all are.

Number 1. is probably the anhydrous MgSO4.
Number 2. is probably a hydrated form, MgSO4.n, but the question is which one. n can be 1,2,6,7,or 8. Far and away the most common is the heptahydrate (n = 7), Epsom salts. This is the form brewers usually use.
3. The anhydride is a powder and Epsom salts are certainly crystaline but I don't know for sure.

The difficulty comes when weighing them out. The anhydride will quickly absorb moisture from the air making it difficult to weigh accurately. Uncertainty in the value of n makes it hard to figure out how much to use. The heptahydrate is half water i.e. its molecular weight is twice that of the anhydride and for a given level of sulfate or magnesium you would need to use twice as much (by weight).

It is probably safe to assume that the crystals are heptahydrate (Epsom salts) as I believe that is the most common mineral form.

There are few brewing applications where magensium sulfate is necessary as the malt itself contains more than enough magnesium for enzyme co-factor duty.

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