Brun'n water Gypsum Calculations (dihydrate vs hemihydrate)

[dttk0009]

Hey folks,

Pretty much all of the gypsum available to me from the home improvement stores here is the hemihydrate variation (CaSO4 x 0.5H2O). Before I resort to ordering the dihydrate variety from the internet, I thought I'd ask if there is any significant difference to using hemihydrate in place of dihydrate in respect to calculations that I got from Bru'n Water.

If so, what adjustments do I need to make to get the amounts of hemihydrate needed in place of dihydrate? Are any readjustements even needed? Is it safer to just order the 2H2O variety off the net?

Thanks!

 

[mabrungard]

So, is that gypsum at the home improvement store saying it's food-safe? If not, I would seek a better and safer supply.

You also need to be aware that if that gypsum was dehydrated at too high a temperature, it can become partially-insoluble. That isn't of much use in brewing in that case.

 

[MaxStout]

Gypsum? Home center store? I hope you're not getting drywall compound.

If you can't get food-grade gypsum from your brew store, you can order it from Amazon.

 

[dttk0009]

Haha, I assumed 'food grade' wouldn't make much of a difference here since it's the same chemical compound in the end...but yes, it's basically drywall compound (called Gips here) and other German speaking forums discussed using this variety.

I hadn't found any cheap source or availability of gypsum as food grade here other than online, and in those cases, vastly more expensive (due to shipping costs), but I might just bite the bullet and order it, just a couple of bucks in the end.

Would this particular brand work?
https://www.amazon.de/dp/B076FB8P4P/?tag=skimlinks_replacement-20

 

[ajdelange]

The English translation of "Gips" is "Plaster of Paris" which is the hemihydrate of calcium sulfate. Add water to it and you get gypsum, the stuff of dry wall or gyprock. Calcium sulfate is calcium sulfate but I think we can feel a little more secure in consuming food grade gypsum as opposed to Plaster of Paris. My LHBS was out of gypsum at one point so I went to the hardware store and bought some Plaster of Paris. When I got home with it I couldn't quite bring myself to put it into my beer.

The stuff linked in #4 is food grade and would be suitable.

FYI: The molecular weight of CaSO4.2H2O is 172.2 of which 36 belongs to the water leaving 136.2 for the CaSO4. Plaster of Paris only has half a water molecule so its molecular weight is 136.2 + 9 = 145.2. Thus if one gram of gypsum is called for 145.2/172.2 gram of Plaster of Paris will give you as much CaSO4.