Thu Mar 10, 2011 7:32 am
The relative strength of the two acids depends on the pH. In taking water from pH 7-8 to pH around 6 citric is, on a weight basis, about 6% stronger than lactic so that if you used 1 gram of lactic you'd get the same effect with 0.94 grams of citrtic. OTOH in lowering mash pH (where you are going from pH around 5.7 to 5.3 or 5.4 citric is about 2% weaker so that if you had used 1 gram of lactic you would have to use 1.02 grams of citric. IOW, they are approximately the same in strength in either case.
That aside, I'd follow the advice to do a test with some of the water. I would think that pH strips would be accurate enough in this case. Do you really care about setting the pH of the sparge water accurately? But I do think every brewer should own a pH meter.