Iso-a-acids (IAA) and reduced IAA can be used as beer-specific ingredient congeners to confirm beer consumption when detected in blood and other specimens using a UHPLC?MS/MS method. Recent analysis of postmortem casework demonstrated a high prevalence of beer consumption and the possibility of providing the source of alcohol in forensic casework. Research outlined in this manuscript has examined the degree to which the interval after death and quality of blood affects the concentration of IAA in postmortem cases. Postmortem whole blood and serum were analyzed in cases where natural or reduced IAA groups were detected. The trans-IAA, cis-IAA, and tetrahydro-IAA (TIAA) groups were subject to postmortem redistribution, although only weakly associated with the length of time from death to collection of specimens. Serum had threefold higher concentrations than blood for trans-IAA, cis-IAA, and TIAA. These studies confirm that although postmortem concentrations cannot be easily compared to concentrations found in living persons the presented findings do provide some understanding to assist in interpretation where the confirmation of beer consumption is required in forensic casework.