Originally Posted by ThreeGnomes
Well, unfortunately.. my question starts from a competition we are in on Sunday.. It's called Iron Brew.. We only know two things. The batch size (5 G) and the Yeast (WLP001) We have no idea what the grains are and we don't know the hops. We can weigh the grain.. Be nice to know more
It doesn't matter what the grains are in terms of the rule of thumb. Of course in actuality it does but the rule of thumb assumes that the buffering capacity of most grists is about the same. The fact that it varies somewhat is why the rule of thumb is a rule of thumb and not much more. The amount you need also depends on the pH of the mash
without the addition of lactic acid/sauermalz. If it is 5.7 and you want 5.4 then you would add 3% sauermalz or the equivalent amount of lactic acid. If it is 5.2 then you would add -2% i.e. alkali with the equivalent strength of the lactic acid in 2% sauermalz.
I didn't work out the equivalent acid for a pound of sauermalz because I try to force people to do a little thinking for themselves but the rest of the story is that pound of sauermalz weighs 454 grams and at 2% lactic acid that implies each pound contains 0.02*454 = 9.08 grams. Thus if your mash pH comes in at 5.65 without acid and you want 5.4 that would require 2.5% sauermalz. Assuming 10 pounds of grain you would need 0.25 lbs sauermalz equivalent to 0.25*9.08 = 2.27 grams of lactic acid. If you are using 88% lactic acid solution you would need 2.27/0.88 = 2.58 grams of the solution. As the density of an 88% solution is 1.206 grams/mL that's 2.58/1.206= 2.14 mL. Putting it all together in one formula
mL_88%Lactic = ((pH_w/o_acid - desired_pH)*10/100))*weight_of_grain*454*.02/.88/1.206
mL_88%Lactic = 0.86*(pH_w/o_acid - desired_pH)*weight_of_grain
Obviously it would be best to use a good pH meter to measure the pH w/o the lactic acid and then make the adjustment based on what you measure. Barring that then you would have to WAG based on what you know about the beer and the water. Given that you are using WLP001 we can assume it is an ale. For a pale ale 2% sauermalz is a good guess if the water is of moderate carbonate level. If the water is low in carbonate you might want to decrease that and if the water is higher increase it. As the amount of crystal malt increases the amount of sauermalz/lactic acid should decrease. For stouts don't use any.