Analysis of Distillate Fractions Collected from a Small Commercial Pot Still Using NMR and GC-MS

In an effort to evaluate the performance of a 5-gallon pot still in separating yeast-derived congeners during the distillation of a grain-based distiller’s beer, the distillates of a fermented mash of cracked corn, malted barley, and wheat were characterized using 1H NMR spectroscopy and GC-MS. A quantitative comparison using these two techniques is uncommon. Results revealed significant variation in congener concentrations across runs, with a notable discrepancy in the third run possibly due to bacterial contamination, as indicated by high 1-propanol levels. Key congeners, such as acetaldehyde, ethyl acetate, furfural, phenylethanol, and 1,1-diethoxyethane, showed expected distillation behavior across ten fractions, based on their respective boiling points. However, methanol and 1-propanol showed a fairly flat concentration profile across all ten fractions, while those for ethyl octanoate and ethyl hexanoate decreased rapidly and were undetected at fraction 5. White dog (unaged whiskey) fractions from column and combination stills were also analyzed, and the results demonstrate that the small 5-gallon still separates congeners as well as these stills. Finally, a comparison of congener concentrations demonstrates that NMR and GC-MS do not yield identical concentrations of congeners, despite exhibiting similar trends in congener concentrations in the fractions from the still, with GC-MS suggesting higher levels.