The issue is you lose Ca throughout the whole process so basing starting Ca amounts off a ward labs report of a finished beer can be rather misleading. Also everyone raves about the soft mouthfeel of Hill Farmstead... their beers have a decent amount more Ca in them than Tree House beers.... it’s not just Ca content...
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CALCIUM LOST IN THE MASH:
NOW IT GETS A LITTLE COMPLICATED. Any calcium added to the mash is reduced by two processes:
a) Removal of bicarbonates resulting in acidification of wort and lowered pH: “Note that it takes a single calcium ion to remove two bicarbonate ions, and remember that you want to have 50-100 ppm calcium remaining in your water for mash activity.”
…[to precipitate bicarbonate with calcium] and its removal will encourage the reaction to continue until either the bicarbonate or the calcium is consumed."Zymurgy article, special GRAIN issue, 1995, p. 35 - by Ginger Wotring – author of the BJCB Water section to prep for the BJCB exam)
So whatever your bicarbonate level is, it begins getting precipitated in the mash by calcium mixing with phosphates from the mash at about 158*F. This doesn't take very long and could be accomplished in 10-15 minutes. So, if you have 100 ppm bicarbonate you will 'consume' 50 ppm calcium while precipitating out the bicarbonate.
In addition, you lose 50-60% of the calcium in the spent grains when you sparge. "Because of the precipitation of CA in these pH control reactions, there is a considerable reduction in the calcium ion concentration during wort production; about 50-60% of the CA ions present during mashing (either present in mashing liquor, or as added salts, or derived from grist materials) will be lost with spent grains and trub." Priest, p. 116
So say you started with 100 ppm calcium in the mash (35 from the malt and 65 by salt additions (calcium sulfate or calcium chloride, e.g.). You then subtract 1/2 of whatever your bicarbonate level is, say 50, leaving you with a residual of 75 ppm calcium. Then you lose say 55% of that in the spent grains. Now you have 34 ppm surviving into the boil kettle.
CALCIUM NEEDS IN THE BOIL KETTLE/FERMENTER
"It has been estimated that a minimum level of 100 mg/l CA ions is required for good quality protein break formation." Priest, p. 113
"Yeast flocculation is improved by calcium; most yeast strains require at least 50 mg/l for good flocculation..." Priest, p. 113.
SO, you need 75-80 in the mash; and a net of 100 in the boil which also addresses the yeast needs in fermentation.
"Another recommendation is that calcium should be in the range of 20-150 ml/l depending on the beer that is being made." Briggs, p. 65