water chemistry noob question

[jack_a_roe]

so just starting to make water adjustment but am missing a basic tidbit regarding water volume. do i make adjustments on just my mash water volume? or sparge water? definitely not both?..does it have to do with when im adding the adjustments? in the mash vs in the sparge water? just bought the water book that i will have soon but wanted to brew a hoppy ipa before then and just wanted to get the minimum of info first. all im going to do is add gypsum becasue my sulfates are at 4 ppm which obviously needs to b upped quite a bit

 

[MrHadack]

Add the gypsum to both mash and sparge water, because it is all water that is going into your beer.

The reason for adding gypsum or other salts to water is mainly to change the flavor profile of the beer, and to a much, much lesser extent change the pH of the water (you should rely primarily on acids for changing the pH of the mash, and not salts.)

Let's look at it this way: pretend you are doing a batch that requires 4 gallons of mash water and 4 gallons of sparge water and you're using distilled water. You add an amount of gypsum to the mash water to raise the sulfate up to 120 ppm. If you didn't add any to the sparge water, by the time all the water is in the kettle, you've potentially diluted your sulfate levels in half to 60 ppm: 4 gallons of 120 ppm + 4 gallons of 0 ppm. (For simplicity sake I am not taking grain absorption into account.)

 

[jack_a_roe]

So i should be making two additions, makes perfect sense, thats exactly what i wasnt getting why you dont use pre boil volumes to get the addition amounts. and im assuming one should be compensating for grain absorption for the first addition by that comment.

 

[MrHadack]

and im assuming one should be compensating for grain absorption for the first addition by that comment.

Well, you don't have to take grain absorption into account when figuring out how much gypsum to add if you're adding it equally to all of your source water. For example, if all your source water (sparge and mash) has 120 ppm sulfate, and some of it gets absorbed by the grain, all the water that ends up in the kettle is still going to be 120 ppm sulfate.

I suggest having a look at the Bru'n Water spreadhseet which can be downloaded HERE. You can tell it the volume of your mash water and the volume of your sparge water, and how much of any salt you want in total (120 ppm sulfate, for example) and it will outline exactly how much of each salt you need to add independently to the mash and sparge water according to how much volume it comprises related to the entire batch. It takes the guess-work out.