AbstractThe mass spectra of methyl maltol (3‐methoxy‐2‐methyl‐4H‐pyran‐4‐one) and methylallomaltol (5‐methoxy‐2‐methyl‐4H‐pyran‐4‐one) and a number of deuterium labelled analogues have been studied in detail. The two pyrones have common fragmentation pathways, all of which can be traced back to a primary rearrangement of the molecular ion. The loss of water from the molecular ion occurs by two processes, both involving the methoxymethyl protons. The loss of methyl from the molecular ion also occurs by two routes, only one of which involves the meth