Hygroscopic Brewing Salts

[corax]

I'm a fan of the "Measuring Calcium Chloride" thread, but I'm wondering what other common salts we should take similar care to measure out?

I note that Calcium Sulfate is sold by chemical suppliers as either anhydrous or dihydrate. Which do we typically get when we buy "Gypsum" from the homebrew suppliers? Is it as unstable and thirsty as Calcium Chloride?

 

[mabrungard]

Magnesium chloride is also hygroscopic.

 

[cire]

Gypsum is calcium sulfate dihydrate and does not absorb water as quickly as calcium chloride, but should be kept sealed and in a dry location.

 

[ajdelange]

I'm a fan of the "Measuring Calcium Chloride" thread, but I'm wondering what other common salts we should take similar care to measure out?

The other 'salt' that will turn soupy is lye but I don't think that many brewers use it.

I general all salts take up some water to the extent that fine (analytical) work requires drying of them in an oven followed by cooling in a dessicator. Such precusion is not generally necessary in brewing where you can really think in log units rather than absolute (IOW doubling of an ion concentration, at whatever level, is likely needed for a clearly perceptible change in effect.

I note that Calcium Sulfate is sold by chemical suppliers as either anhydrous or dihydrate. Which do we typically get when we buy "Gypsum" from the homebrew suppliers? Is it as unstable and thirsty as Calcium Chloride?

Depends on the form. The gamma anhydrite (CaSO4.nH2O n < 0.05) is sold as a dessicant (Drierite). The hemihydrate (CaSO4.0.5H2O = Plaster of Paris) obviously takes up water on its path to becoming Gypsum (CaSO4.2H2O) but is not deliquescent. The stuff we buy from the LHBS is gypsum and it is quite stable being what sheet rock is made of.