Involved in D-altritol catabolism. Catalyzes the oxidation of D-altritol to D-tagatose. D-altritol + NAD(+) = H(+) + keto-D-tagatose + NADH Binds 2 Zn(2+) ions per subunit. kcat is 1.9 sec(-1). Carbohydrate metabolism. Up-regulated by growth on D-altritol or galactitol. Deletion mutant cannot grow on D-altritol. Does not exhibit a growth defect when grown on D-galactitol. Belongs to the zinc-containing alcohol dehydrogenase family.