My understanding of acid malt being used at that quantity is that it's often used to help with the mash pH, moreso than necessarily trying to add an acidic quality to the beer's flavor profile. That's my understanding of where acid malt originated; German brewers needed a way to adjust mash pH without adding any chemicals directly (Reinheitsgebot). That's how I've used it; I have crappy efficiency, I *think* because of pH so I've played around with adding a little acid malt.
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