Any references as to how much of the minerals in the mash water make it to the kettle?
To a first order, ppm in = ppm out.
However, there are certain other factors involved such as the precipitation of Ca by HCO3.
Also, will the grain retain water but not minerals such that the mash water out has a higher ppm? Or is it just the opposite in that the grain retains minerals and not water making the mash water out have a lower ppm?