brianl wrote:We can definitely help you build coffee water but the topic on hand deals with the gcw.
Yes. Last time it came up on HB was here: Water formula
I think a lot was discussed there but never arrived at a simple formula for adding pickle crisp and baking soda to distilled in order to hit SCAA standards. Even though it's a bit off topic, I'll bite and provide what I think is a formula below.
brianl wrote:The only thing I struggle with is calculating pH.
Same here. I did Henderson-Hasselbach calculations for blood chemistry ages ago in biochemistry classes, but not even sure they apply here. Dang CO2 enters into the equation, which affects the bicarbonate/alkalinity as well as the pH.
Off Topic stuff follows:
What would I add to distilled in order to get close to the SCAA target
Calcium hardness - 68 mg/l (as CaCO3) (= 27 mg/l Ca++)
Alkalinity - 40 mg/l (as CaCO3) ( = 49 mg/l HCO3-)
Sodium - 10 mg/l (OK if less than 30 mg/l)
TDS - 150 mg/l (75 - 250 mg/l OK)
pH - 6.5 - 7.5
So doing a crude calculation, and using just calcium chloride* and baking soda, I came up with the following, using yet another of our beer-brewing brother's handy calculators:
From calculator at http://www.brewersfriend.com/water-chemistry/
Note that we are talking 10 gallons here, juts half a teaspoon of baking soda does 10 gallons!
Alas, this calculator also doesn't try to do the pH calculation. I'm guessing it might come out on the basic (high side) of the SCAA ideal. That's OK, since we have a chloride level of 47 mg/l and we don't want to worry about corrosion. The TDS should come out in the ballbark since we are adding 6.3 grams of stuff to 10 gallons, which would be about 165 mg/l, and in practice would be a smidgen less because of some HCO3 converting to CO2/H2O.
If I were doing this (making coffee water out of minerals and distilled) I think I might go with a bit less Ca++ and add some Mg++. SCAA water spec doesn't say anything about Mg, but some believe it to enhance the extraction better than Ca++.
I did try out the nice speadsheet that Fred (MerlinWorkd) provided but couldnt get it to behave on my Mac's Numbers
*Note: The calculator app doesn't specify what form of CaCl2 it expects, but the Ca++ concentration comes out right if you assume that it is pure dihydrate, i.e. 2 H20 molecules are associated with each CaCl2. Pickle Crisp I believe is dihydrate CaCl2.