All numbers are parts per million. Calcium is the principal mineral of hardness, having come from the water's passage over limestone, dolomite, gypsum or calcified gypsiferous shale. Calcium increases mash acidity and inverts malt phosphate. In appropriate amounts, calcium is advantageous to the brew. It stimulates enzyme activity and improves protein digestion, stablizes the alpha amylase, helps gelatinize starch and improves lauter runoff.
Calcium also extracts fine bittering principles of the hop and reduces wort color.
A calcium precipitate formed with potassium phosphate improves hot-break flocculation. During aging, it improves clarification, stability, and flavor of the finished beer. In excess, however, calcium precipitation with organic phosphates interferes with runoff filtering and robs the wort of phosphate, a necessary yeast nutrient. Magnesium is the secondary mineral of hardness. It is essential as a co-factor for some enzymes and as a yeast nutrient.