[tschmidlin]

I found this paper that determined that calcium is required, but only at a rate of "one atom of Ca2+/molecule of enzyme"     They also found that the enzymes were "irreversibly inactivated by incubation in low Ca2+"  So plenty should be carried over from the malt, even if there's not that much to start with.  It's interesting though, that they found a 10-fold difference in binding affinity between the different isoforms of the enzyme.

I also found this one that shows it is much more important for malting (activity on insoluble starch) than mashing (activity on soluble starch), but even then only one of the enzymes showed a significant benefit on insoluble starch from higher levels of calcium, and both were inhibited by very high levels.  For soluble starch, there isn't much difference between either enzyme over the range of calcium concentrations tested.

Here's a nice figure from the paper, panel A is insoluble starch, panel B is soluble starch.  And for anyone reading this who doesn't know, you can convert mM calcium to ppm calcium by multiplying by 40.



<edit> I see you found the same paper

[mabrungard]

I'll agree with Kai that excess Ca is not needed for conversion and enzme activity.  But, there are reasons to have a moderate Ca concentration in the water.  The primary reason is to provide a medium to precipitate undesirable components from the wort in the mash and the boil. 

Last month, I polled a number of brewers that had indicated that they sometimes suffer from beerstone in their systems.  In all cases, low calcium concentration in their brewing water was confirmed.  Calcium is an important complexing medium for precipitating oxalate from wort.  The same thing applies to other hop and protein complexs that also drop out in the mash and boil. 

I'm not sure that a minimum calcium concentration of 50 ppm is really the "minimum" that we should strive for in our brewing water, but I am in agreement that having a lot more calcium in the brewing water does not appear to be needed. 

Good work by Kai and Tom.  I learned something from them.

[Thirsty_Monk]

I want to have enough calcium in my beer that I do not have to drink milk   

I apologize for this comment up front.

[hopfenundmalz]

Martin - Any advice as to what I should be targeting for the Ca addition to RO water?  100 to 150 ppm?

[mabrungard]

I don't see a need to have a high calcium content in brewing water, except as needed to balance elevated sulfate, chloride, bicarbonate content.  I do not know what the minimum calcium should be, but I know that one of the major American brewers that I have consulted with uses a nearly Pilsen-like calcium content of around 13 ppm.  I'm sure they would have beerstone problems if they didn't have a very active cleaning protocol.  With regard to a minimum that I would use...I suggest that 40 to 50 ppm calcium would be safe and provide adequate calcium for the precipitation reactions. 

With regard to the upper calcium limit, it will depend upon the other ions that you desire in your water.  For instance, Burton water has huge sulfate, chloride, and bicarbonate concentrations that would be difficult to balance if you didn't allow high calcium concentration.  Increasing the magnesium or sodium concentrations to balance the high anion concentrations would quickly produce undesirable flavor in the finished beer.  Many of the water profiles from world brewing centers have calcium concentrations approaching 100 ppm and Burton and Dortmund are over 200 ppm.  Big numbers, but still suitable for brewing.

Another thing that I've recognized for water profiles, the cation content has to increase as the bicarbonate content is increased for darker beer styles (increased RA for darker beer).  Again, you should try to keep the magnesium or sodium content relatively low and increase the calcium content as needed to balance the increased bicarbonate concentration that is needed to buffer the effect of the dark grain acidity.  So, the bottom line is that water for darker styles should have higher calcium content than needed for pale styles.