Catalyzes the 3-beta-hydroxylation of 2S-flavanones to 2R,3R-dihydroflavonols which are intermediates in the biosynthesis of flavonols, anthocyanidins, catechins and proanthocyanidins in plants. 2-oxoglutarate + a (2S)-flavan-4-one + O2 = a (2R,3R)-dihydroflavonol + CO2 + succinate Binds 1 Fe(2+) ion per subunit. Secondary metabolite biosynthesis; flavonoid biosynthesis. Belongs to the iron/ascorbate-dependent oxidoreductase family.