Residual Alkalinity Calculations

[Nosybear]

One feature I'd like to see is to have the recipe builder calculate and display recommended residual alkalinity values (high, low, and midrange) based on the color of the beer being brewed. The formulas are (for American units):

Low: SRM *12.2 - 122.4
High: (SRM - 5.2) * 12.2
Midrange: Low + (High - Low)/2

These formulas are taken from "How to Brew" by John Palmer. His current spreadsheet has taken the SRM-based calculations out and relies on the style to give the values. I prefer to use the values from the actual SRM.

 

[jeffpn]

Is that midrange formula right? It looks to me that your formula simplifies to High/2. I would think it should be (High+Low)/2

 

[Nosybear]

It's the formula that works in my edited spreadsheet.... I think you're taking out the parenthesis when you shouldn't - order of operations, you have to do the division term first. Think of it this way: I'm starting with the low value, then adding half the distance to the high value to get the midrange.

 

[jeffpn]

Yeah, I see that now. I've never seen a formula to calculate an average written that way. But it works. Essentially, you're saying add half of the value of the difference between the high and the low to the low, where I'm used to seeing add the value of the high to the low, and divide that sum by two. Either way produces the same answer, but I don't like your new math!! :lol:

 

[Nosybear]

...and you're right - easier way. I never bothered to simplify that equation. Can I have a beer with that crow....

 

[Josh (Brewer's Friend)]

Hi guys, thanks for the suggestion. I've added this calculation to the recipe builder now, so you should see a target RA range under the "More..." dropdown in the builder:


Hope that helps - let me know if you see any issues with it.

Cheers!

 

[Myers]

Added to the recipe builder is Recommened Residual Alkalinity, with John Palmer listed as the source. In your posting you refer to it as a target RA. The range shown relates to the color of the style selected. If you would, please explain how this should/would be considered a recommended or target RA for recipe building purposes?
In his book, Palmer refers to it as "suggested beer color/style guide for RA mash pH for a 100% base malt mash based on the water profile." In other words, for a recommended or target RA range to make any sense, it must be considered relative to the recipe builder's water profile and the RA/pH it would produce from a 100% base malt mash. But the recipe builder's Recommended RA does not put it in any such context and seems to imply that the Recommened RA range is some kind of result to target and achieve.

So what is important for achieving good mash results for each and every beer style: realizing a mash within a specific RA range, or realizing a mash within a specific pH range? Palmer states in his HTB book (page 158), "Let me state the goal right up front: for best results, the mash should be 5.4 to 5.8 when measured at room temperature."

I have found that using BF's brewing water calculator I am able through the salt additions section to achieve a selected water target (depending on my desired beer style) for my source water -- which fortunately is very low in minerals and corbohydrates -- and an acceptable mash pH. My point is, I'm very pleased with BF and specifically its water calculator section; I'm just not clear on the usefulness of its listed Recommended RA range.