Synthetic dipeptides of varying hydrophobicity were used as a model system to investigate the feasibility of reversed protease action as a means of improving the flavor of bitter peptides found in protein hydrolysates. The four different proteases tested were able to convert hydrophobic dipeptides into an insoluble precipitate, but with different efficiencies. Hydrophilic dipeptides did not give detectable condensation or precipitation. Solid-state and solution NMR were used to monitor peptide bond formation in 1 3 C-labelled peptides. NMR and MS analyses showed that the products consisted of higher oligomers of the original peptide. Bitterness decreased in the order starting with dipeptides > whole reaction mixtures isolated precipitates. Taste improvement correlated with peptide bond formation and the formation of insoluble material. These observations indicated that the condensation reaction was driven by precipitation of insoluble reaction products and that this process is a potential means to improve the flavor of bitter peptides extracted from protein hydrolysates.