Why so much calcium in some brewing waters?

As pointed out in articles published in The New Brewer and Zymurgy, high calcium content is not always desirable. For ale brewing, 50 ppm Ca is typically adequate to promote adequate flocculation and clearing. But the calcium content can be much lower when brewing lagers. So why do some profiles in Bru'n Water have much more than 50 ppm Ca???

The Pale Ale profile has very high calcium content due to our desire to also have a lot of sulfate in that water. Sulfate is an important component for helping the beer finish dry and allowing the bittering and hops to stand out. That sulfate anion has to be paired with some cation. You generally have the choice of calcium, magnesium, or sodium cations. Since sodium and sulfate don't taste very good together at high concentration, your choices are functionally limited to Ca and Mg. This is a reason that the magnesium content of the Pale Ale profile is somewhat high. Epsom salt (MgSO4) use in the Pale Ale profile enables the brewer to avoid adding too much calcium while still boosting the sulfate content to the high levels that are often desired in a Pale Ale. You just have to be careful to avoid adding too much Mg with the Epsom salt addition since it can have negative taste effects as its concentration in water exceeds 40 ppm Mg.

Adding magnesium to brewing water is typically not necessary since malt provides all the Mg that the yeast need. But in the case of highly mineralized water profiles such as Pale Ale profile, the use of Epsom salt helps avoid excessive calcium content in the brewing water which can prematurely flocculate some yeasts. It is a worthwhile trade-off if you want plenty of sulfate in your brewing water.