The problem is that, contrary to popular belief, Sauermalz (Acid Malt) doesn’t behave or have the same characteristics as Lactic Acid.
In fact, AFAIK, Sauermalz is actually treated with Sauergut (Biological Acid), which also can’t be modeled as xx% Lactic Acid.
A Quote from A.J. deLange:
“The fit was done over the region pH 4.6 to 6 and, as the graph shows, the match is perfect at about 5.45. In other words, 31.3 grams of lactic acid are equivalent in acidity to 1 kG of Weyermann’s Sauermalz at pH 5.45. At any other pH this equivalent does not hold. Thus at pH 5.45 Weyermann’s Sauermalz has an effective lactic acid content of 3.13%.”