As brewing salts age

While weighing out water salts for my last brew it appeared that the volumes were noticeably smaller than expected. I measured them out and, sure enough, they were considerably smaller than the measured dosage. I buy my salts by the pound and store them in canning jars so it may be a year or two before I use the last of a pound. They do absorb water, even here in the desert, so I can imagine more humid climates are much worse.

I have always heard/read that weighing your salts is more accurate than measuring. I would argue that weights change much more quickly than volumes do as moisture is absorbed, so that accuracy diminishes greatly over time.

I suggest comparing measured amounts to weighed amounts periodically, especially if your salts have been stored for any period of time.

Here are the dry weight grams/teaspoon amounts for your reference:
Calcium Sulfate 4.0
Calcium Chloride 3.4
Magnesium Sulfate 4.5
Sodium Bicarbonate 4.4

Most of this salts can take different amounts of water, for example Calciumsulfat can come as CaSO4, CaSO4*2H2O or even CaSO4*1/2H2O. I would argue that the longer you got your salts the more salts with higher water incorporated you get.
This should usually be no big deal, but of course if you weigh in CaSO4*2H2O you weigh in 2 molecules of water per molecule of CaSO4 thus leaving you with less CaSO4.
You could simply calculate the weight you need by following formular

m(CaSO4*2H2O)=n*CaSO4*M(CaSO4*2H2O)
m being the mass, n the amount of the substance (mol) and M the molar Mass
To know how much CaSO4 you would need just calculate
n(CaSO4)=m(CaSO4)/M(CaSO4)
If you look up CaSO4 you should find the molar Mass at no time.

Do this once for all the salts you use, and use air-tight containers and you should have no big troubles. I also would usggest already buying the hydrated salts, they are cheaper and wont hydrate any further (as long as the container is closed)

Thanks mrmarbod, but I'm no chemist. Hopefully your tip will help some who are not as old and simple minded as I am.

BOB357 said:

Thanks mrmarbod, but I'm no chemist. Hopefully your tip will help some who are not as old and simple minded as I am.

Click to expand...

+1 molar mass?!?!  woah!!

I see, I calculated it for you.
Here are the factors for the most common hydrates
Calciumsulfat: 1,26
Calciumchlorid: 1,65
Magnesiumsulfate: 2,04
Sodiumbicarbonat: 1

Simply multiply how much salt you want in your water with the factor and you get how much you should weight in. This only applys when your calculated salts would be the waterfree versions.
Hope this helps.

Thanks.

Good man, thank you!

Please consider this as theretic approach, maybe try it out once or twice, some slats have more than just one kind of hydrate etc.
It would help when you could show me the information on your salts, (like name company content etc.) Maybe we can get even better calculations going.

Thanks again, but I'm sure the problem stems from the time frame and method of storage I practice. I feel a lot more comfortable to compare weights and measured amounts rather than try to understand chemistry. Don't feel like you're hijacking this thread though. I think there are some who will read and learn from your input.