ABSTRACTMethods for detecting corn syrup in barley (Hordeum vulgare L.) malt extract were evaluated. Twelve samples representative of commercially available 2‐rowed and 6‐rowed malting barleys were malted. Extracts prepared from the finely ground malts were analyzed for 13C/12C ratios, expressed as δ13C, and concentrations of protein and sugars. The 13C/12C ratios were sufficiently different to distinguish corn syrup from malt extract. By calculating the mean values for the barleys, it was determined that a δ13C > ‐24.3‰ indicated that the malt extract had been adulterated with corn syrup (99% confidence). Protein concentrations <4.5% (2‐rowed malt) or <5.0% (6‐rowed malt) of the extracts also indicated probable adulteration with corn syrup, which is devoid of protein. Because of differences in sugar concentrations between the malt extracts and corn syrup, carbohydrate analysis also indicated probable mixtures. These findings were confirmed by analysis of extracts from composite 2‐rowed and 6‐rowed barley malts that had been mixed with known quantities of corn syrup. The regressions for δ13C, protein concentration, and most sugar concentrations against percent dilution with corn syrup in the mixtures were significant.