The evolution of homochirality from a prebiotic environment has long intrigued scientists. Here we report how highly enantioenriched solutions may be produced by manipulation of amino acid phase behavior, a concept that has far-reaching implications for prebiotic chemistry. We demonstrate that the eutectic composition of aqueous mixtures of L and D amino acids may be tuned by the addition of achiral dicarboxylic acids that cocrystallize with chiral amino acids. We find that, in several cases, these systems yield new eutectic compositions of 98% ee or higher. This work suggests a forerunner of modern crystal engineering that provides a general and facile mechanism for the evolution of homochirality as well as a conceptual advance for the separation of enantiomers of molecules forming racemic compounds.