Sour Mash Ph Equation

[zandrsn]

Hi all, I'm making a foreign export stout soon. My plan is to sour mash 5% of the base grist in order to lower my mash ph to 5.2-5.3. I'm wondering if anyone knows of a calculator or equation that will help me figure out how much a specific volume of sour mash (at a specific ph, let's say 3.8-4) added to my mash will lower the ph of the entire mash. I will test it with my ph meter after adding some of the sour mash back to the main mash, but have been wondering for a while if there was an easier way to figure this out.

Something like: X Liters at ph Y = decrease of mash ph by Z % or Z ph points

Thanks for you thoughts!

 

[erikpete18]

Yeah, there's not really a way to consistently do that, since its impossible to know what the buffering capability of the main mash is. Someone may have tried out a bunch of different additions and calculated a rough equation based on their system, but there's no saying what that will do in your system with your malt and water. You'll probably just have to add some, take a measurement, add some more, etc etc until you hit your point. If you take good notes that would give you a place to start in the future if you're trying to do this again, but I'd probably still plan on aiming lower than expected and slowly adding more until I got where I was going.

 

[kingwood-kid]

Just curious, why do you want to use soured beer (instead of acid or acidulated malt) to adjust the pH? I ran a test stout recipe through http://www.brewersfriend.com/mash-chemistry-and-brewing-water-calculator/ I used RO water as the default, but a sufficiently roasty stout (1.75lbs 450L malt) would have a mash pH of 5.3 all by itself. A few drops of acid or a few ounces of acidulated malt can also have a pretty large effect.

 

[pdxal]

Doesn't 1% sourmalz reduce the mash ph by 0.1? Perhaps that would be easier, or at least provide you with an idea of how much you'll lower it by with a sour mash.