Brewing and stewing: the effect of culturally mediated behaviour on the oxygen isotope composition of ingested fluids and the implications for human provenance studies

‘Small beer’, ‘wort drinks’ and ‘pottage’ may have been regularly consumed by children during the Medieval Period. This culturally mediated behaviour could have affected the oxygen isotope composition of their water intake beyond that which is accommodated in the current conversion equations used in archaeological studies to assess environmental origins. Experimental data shows that brewing may increase the δ18O value of ale by 1.3‰ over that of the initial water (‘liquor’) used, boiling water to make hot drinks raises the δ18O value of the fluid consumed by ∼0.4‰ and slow-cooking using a large stew pot results in an increase in the oxygen isotope composition of the ‘pottage’ by an average of 10.2‰ after 3 hours of cooking. Thus, if ingested fluids included 20% from ale, 10% from ‘teas’ and 20% from stews (the latter increased from −7.0‰ to +3.2‰ by three hours of cooking) then the overall effect on the calculated drinking water value from the tooth enamel will be +2.3‰.