The regional timing of maize introduction in eastern North America is a long-standing topic of archaeological interest. Most recently, Morton and Schwarcz [2004. Paleodietary implications from stable isotopic analysis of residues on prehistoric Ontario ceramics. Journal of Archaeological Science 31, 503–517] investigated the timing of maize introduction in Ontario through isotope analysis of charred cooking residues adhering to the interior of prehistoric ceramic containers. They interpret their results to suggest maize was incorporated into diets after A.D. 600. We assess their approach and conclusions with stable carbon isotope assays on three sets of experimental cooking residues, evaluating the variable combustion of carbon fractions, contributions of fats and carbohydrates, and the contribution of total carbon. We also undertake multiple resource modeling of two part food mixes with green maize and maize flour. Our results suggest that systematic under representation of maize can result depending on residue composition and that some prior knowledge of C3 plant and animal contents is necessary to interpret stable carbon isotope values on cooking residues. We question the independent use of stable carbon isotope analysis of charred cooking residues as a viable technique for extracting paleodietary information.