Plasmonic excitations in pristine and air-exposed graphene–Ru and graphene–Pt contacts have been investigated by using high-resolution electron energy loss spectroscopy. Loss measurements show that the effects of air exposure are very different in these two systems. While in graphene–Ru contacts, plasmons are completely quenched, plasmons in the graphene–Pt interface show only a frequency shift together with an overall intensity attenuation. These results pose significant questions as regards the stability in an ambient air atmosphere of graphene-based plasmonic devices and indicate a suitable choice of graphene–metal contacts.