onkeltuka wrote:I calculate the mineral amounts based on the TWN, but once I'm done boiling I might have only 60% liquid of that left, so won't I end up with hugely concentrated amount of minerals in that smaller volume of wort?
Look
here at these Brew Strong episodes for more info on water. The 4-part series from 2009 is a great overall course in water (although there is a small amount of incorrect info); I just finished listening to it. In either part 3 or 4 of that series, JZ specifically says that the water should be adjusted pre-boil. Realize that if you're trying to replicate Pilsen or Dortmund water, that is the water characteristic you start with. If a brewer were using water of a certain mineral characteristic, all of the water (mash and sparge) would have the same mineral content.
Obviously, evaporation is the big variable, since higher levels of evaporation will result in higher mineral concentrations in the finished beer. You may just have to learn to make those adjustments based on experience. Then report back here with your findings.
Bru'n Water identifies the same mineral adjustments for both mash and sparge (for the non-BIAB traditionalists who have both). I expect that experienced brewers may adjust their sparge additions or they may just back off on both the mash and sparge additions as you have.
I personally set my TWN as the mash volume in BW, 0 as sparge, and treat the whole TWN. For something like an IPA with high sulfate/chloride ratio, you can always back off on the total ppm while maintaining an approximate target ratio. The only thing that scares me about BIAB is that we are treating so much more water for the mash, so the total amount of minerals is pretty high.
I brewed 29L VIF of Tasty McDole's Janet's Brown Ale yesterday. He posted on the BN forum "FWIW, I raise RO water to Ca-110ppm, Mg-18ppm, Na-17ppm, SO4-350ppm, Cl-50ppm when I make JBA."
According to BW, my adjustments should have resulted in the following: Ca-66ppm, Mg-15ppm, Na-12ppm, SO4-153ppm, Cl-51ppm. I had to add 8g of gypsum, 6.6g of epsom salt & 4.5g of CaCl2 to 13.2 gallons (50L). This was a lot of additions, so I'd rather come up short rather than over-doing it, not to mention that Tasty is a bit more of a hop-head than I am. This is already a very hoppy beer, so I'm scared of overdoing the sulfate and over-accentuating. In essence, you and I are achieving the same result, whether by reducing the minerals based on volume or reducing the target ppm. I'd say that personal experience and perhaps info from other forums (and then sharing here) may be the key to learning more.
my chemistry teacher (I'm at school again now at 38-years of age) recently praised me for asking aloud all the idiotic questions that I do 
