Phosphoric Acid conversions?

[BeverleyBrews]

Hey friends,
I'm trying out a recipe that calls for phosphoric acid, but I'm going to use citric instead based on availability at my local HBS. Do I use the same amount that the recipe calls for? I'm not feeling confident in what I've found online.

 

[VikeMan]

I'm trying out a recipe that calls for phosphoric acid, but I'm going to use citric instead based on availability at my local HBS. Do I use the same amount that the recipe calls for? I'm not feeling confident in what I've found online.

I think several of the mash pH programs out there support citric acid. And the amount to use would definitely be different between those two acids.

But are you saying the recipe called for a specific amount of phosphoric acid? If so, that's a bad recipe, unless it also specifies the water profile. Acids are added to the mash to adjust mash pH. How much is needed (if any) depends on the minerals in the water, as well as the grain bill, and the target pH.

 

[Silver_Is_Money]

I've recently concluded via a series of water Alkalinity neutralization tests (to measured pH's) that citric acid is well more acidic than the mash and sparge water adjustment assistant spreadsheets and online calculators have to date presumed for it. I've modified my software accordingly. I initially suspected this potential after a mash I did of a Kolsch using 2 grams of anhydrous citric acid for acidification and targeting 5.40 pH wound up mashing at 5.10 pH.

I have a (~14 Plato) Dortmunder Export on deck that is expected to yield 64-65 x 12 ounce bottles, and will receive 2 grams of anhydrous citric acid crystals in the mash plus an additional 3 grams of anhydrous citric acid crystals in the boil, for a total of 5 grams. I'm doing this specifically to see if I can taste the added citric acid in this beer at this level of addition. If I can't taste its presence, I will begin to use it more regularly.

Due to dissociation related matters there is technically no 'easy' means to equate one weak acid to another without mentioning a pH target, but for a target of 5.4 pH the ballpark grams to mL's equivalence of anhydrous citric acid crystals to 10% phosphoric acid should (based upon my mentioned recent tests) be on the order of ~0.08 grams of anhydrous citric acid to 1 mL of 10% phosphoric acid.