I can now report that the correlation between RA and SRM that is shown in the How to Brew nomograph is inappropriate
I'd be curious on getting your opinion on the "New and Improved Residual Alkalinity Spreadsheets" that Palmer has posted on his site
dated September 2009. Spreadsheet using U.S. UnitsSpreadsheet using Metric Units
In these spreadsheets, the input is SRM and the output is a range of RA. In the instructions he states:
Darker malts have more natural acidity, and therefore require more residual alkalinity to balance them to arrive at the optimum pH. However, the relationship is a general one – different malts of the same Lovibond color value can have different amounts of acidity. You can use the calculated color of a beer recipe as a guide, but don’t rely on it as gospel to determine the appropriate amount of residual alkalinity; it is a general relationship, like cloud color and rain.
He goes on to say:
Remember, roastier grain bills will have a higher acidity than grain bills composed of caramel and toasted malts. Look at the range of RA present and choose a number that you feel is appropriate to the style of beer you want to brew.
Right or wrong (feel free to comment) this is the way I've been using the spreadsheet. For a desired SRM, use the spreadsheet to calculate a range of RA. Choose an RA target based on the roast level of the malts, then tweak salt additions to accomplish three things simultaneously:
- Hit the target RA which should help get close to the appropriate mash pH
- Stay within appropriate limits for the important ions
- Target a level for the "flavor ions" (Na, Cl, SO4) based on what flavor profile I'm trying to achieve
Palmer also gives the following guidelines (from How to Brew
) for the "brewing range" for each ion:
Ca = 50-150
Mg = 10-30
HCO3 = 0-50 for pale, base malt only
= 50-150 for amber-colored, toasted malt beers
= 150-250 for dark, roasted malt beers
Na = 0-150 (sweetness, round smoothness)
Cl = 0-250 (fullness)
SO4 = 50-150 normally bitter
= 150-350 very bitter
For my water (Ca/Mg/HCO3/Na/Cl/SO4 ~= 35/16/120/34/21/18) I find that when making a light beer (e.g. SRM=5) I often can't achieve the target RA using salt additions without exceeding the "brewing range". In those cases, I add acidulated malt as a source of lactic acid to drive the pH lower. (The spreadsheet allows one to enter mL of Lactic Acid, and one can calculate the amount of acid malt to use assuming it has 2.5% lactic acid by weight.)
Finally, Palmer also notes that
"[T]he chloride to sulfate ratio is known to be a strong factor for the taste of the beer. A beer with a ratio of chloride to sulfate of 1-2 will have a maltier balance, while a beer with a chloride to sulfate ratio of 0,5-1 will have a drier, more bitter balance."
Too bad he doesn't provide a reference, but I'm not inclined to dismiss it out of hand, either. For now, I treat it as a interesting data point, but haven't been using it to target RA or salt additions.