RIS - Water/Bicarbonate level

[Braufessor]

Brewing a RIS this weekend. Planning on using about 70% tap water and 30% RO water - my tap water is High in bicarbonate. In general, I have found good success keeping high bicarbonate in my dark beers. This beer is bigger and darker than your average porter or stout though. My big question is in regard to Bicarbonate.... does this look ok for this type of beer.

12.5% Dark grains (chocolate, roast barley, midnight wheat)

70% Tap/30% RO

.1gram/gallon gypsum
.3 gram/gallon CaCl

Ca = 72
Mg = 16
Na = 7
Sulfate = 42
Chloride = 42
Bicarbonate =212

B'run water projected mash pH = 5.50

Also, if I did the same to sparge water.... would I have problems with alkalinity..... I want to get the benefit of the bicarbonate vs. the acidity of the roast grain. I don't want to worry about astringency/tannin/pH problems from the bicarbonate..... but, I know the roast grains are going to potentially cause a problem with my acidity in the collected wort too.

Thoughts on what the profile looks like right now? Thanks!

 

[ajdelange]

As we're finding in another thread mash pH estimation is pretty much a WAG but given a typical ale malt such as Maris Otter (pHDI 5.7, buffering -46 mEq/kg) and typical black malts (pHDI 4.6 - 4.7; buffering averaging about -50 mEq/kg) you could expect a DI water only (no alkalinity, no calcium) mash pH of about 5.53. Adding calcium at 72 mg/L might drop that to 5.50. Add 3.5 mEq of alkalinity (about 213 mg/L bicarbonate) and the pH goes up to 5.67. At that pH the MO has a proton deficit of only 4.2 mEq (assuming you are mashing 10 pounds of grain in 3.5 gal water), the dark malts a proton deficit of -35 and the bicarbonate + 37. IOW your apparent goal of having the 'benefit' of the bicarbonate cancelling out the dark grains is realized. But the mash pH is too high because after the dark malts and alkalinity have cancelled each other you are essentially stuck with the DI pH of the base malt which is 5.68.
You would be better off without this 'benefit'. Let the dark grains do what they are intended to do and that is lower the mash pH to 5.5. Zero out the alkalinity if you can (and you can by enough dilution with RO (essentially 100%) or neutralization with acid. The base malt proton deficit to pH 5.5 is about 35 mEq and the dark malts have a proton deficit of -28. The calcium provides an additional deficit of -7 so calcium related protons and base malts cancel the base malt at pH 5.5.

Common sense says that you don't want to brew with water with 3.5 mVal alkalinity. It's response to sparge water is even stronger. The alkalinity of the sparge water should be very low.

Given the caveats (I'm guessing that the malts you choose will be like the malts I've measured) you should really do a test mash to see where your pH falls given the particular malts you are actually going to brew with.