Calcium sulfate (hydrated) aka gypsum is used to correct mineral deficiencies in water which is to be used for brewing. It is used in de-mineralized or soft to medium hard water to increase permanent hardness. Calcium Sulfate is effective in eliminating the variations in composition often encountered in water from surface sources. It will help establish proper pH of the mash and the wort and provide sufficient calcium ions essential for enzyme function, kettle protein coagulation and yeast metabolism.
17 gm/hl (0.9 oz/bbl) will increase calcium content by 50 mg/liter.