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Residual Alkalinity prediction from recipe

PostPosted: Fri Mar 05, 2010 6:10 pm
by slothrob
I don't think I've asked for this feature before, but some recent work by Kai Troester has re-stimulated my interest in it, so excuse me if I'm repeating myself here.

I use separate spreadsheets and graphs to predict the Residual Alkalinity (RA) requirement for my water to hit the correct mash pH. Then I use BTP to determine the salt additions needed to hit that RA. I'd find it very much simpler to have that RA prediction made within BTP.

This page shows the formulas Kai derived from his experiments and has a pair of tables at the end that show results from these equations. Essentially he has expanded on the material that John Palmer has been promoting by including the differential effects of roasted and crystal malts on the SRM effect on pH. There is a spreadsheet that includes these calculations here.

It would be great if somewhere on the recipe or schedule page or in the water chemistry window there was a note saying "Suggested RA = X".

PostPosted: Fri Mar 05, 2010 7:54 pm
by jawbox
I would love this feature too. My city water is terrible for brewing and I always build my water from scratch using RO or Distilled.
I'm do the same thing using Kai's spreadsheet then entering the info into BTP. If they could include all this in BTP i think it would make an already good program great.


PostPosted: Sat Mar 06, 2010 10:20 am
by slothrob
Yeah, my tap water is nearly as mineral free as distilled, which is a great place to start from but also means I have to build water for every recipe.

There are some other nice features of these and other water calculators. One is signals, like numbers turning red, that tell you when you drift out of the normal brewing range for the minerals. Also, a flag to denote a Cl-:SO4-- balance that promotes Malty, Balanced or Bitter flavor, is useful. Some of the calculators even allow you to choose a base water and a target water and then tells you how much of which minerals to add to hit that target.

edit: All those features could be nice, but a very simple way to add this feature to start would be to add a SRM range recommendation next to the RA listing in the water calculator. This is relatively easy, knowing that an RA of 0 is ideal for a 7.5 SRM beer, that this relationship changes by 30 RA for every 2.5 SRM change, positive or negative, and that there is a ±30 RA range for any given SRM.

I have a simple equation I use for getting a ballpark RA for an SRM:
(SRM - 7.5) ÷ 2.5 x 30 = RA (±30)

Palmer calculates the two extremes, instead, with:
SRM x 12.2 - 122.4 = Low RA estimate
(SRM-5.2) x 12.2 = High RA estimate

Edit: Kai Troester's equations are much more sophisticated than this simple estimate, taking into account mash thickness and the percent of Roasted Malt. His work is based on actual measurements using modern malts. They also show that Palmer's ideal RA is reasonably predictive for thick mashes and low percentages of Roasted Malt, though the high and lows are off. Palmer's equations seem to fall apart in thinner mashes.