When shiitake mushrooms (Lentinula edodes) are stewed together with beef, the heat and shared cooking environment generate five unique umami peptides that don’t appear when the ingredients are cooked separately. These peptides originate from shiitake proteins and significantly heighten savory intensity by enhancing both umami and saltiness, which is why co-stewed shiitake and beef tasted noticeably richer despite having similar glutamate- and nucleotide-based EUC values. Molecular modeling showed the peptides bind stably to the T1R3 taste receptor, explaining the final depth of flavor.