A bio-based binder system for use in preparing foundry molds. In a preferred embodiment, the system includes the use of a) a polyermizable hydroxyl -containing component comprising a saccharide, b) an isocyanate component, and c) a catalyst, and preferably amine catalyst, component adapted to catalyze the polymerization of a) and b), in the presence of a foundry aggregate such as sand. The system can be used in any suitable manner, including in either a cold box process or no bake process as described herein.