Spirit Distillation: Monitoring Methanol Formation with a Hand-Held Device

Methanol occurs naturally in most alcoholic distillates. Yet, suitable detectors to check liquor adherence to legal limits and, most importantly, monitor in situ methanol content during distillation are not available. Usually, distillers rely on error-prone human olfaction while "gold standard" liquid or gas chromatography (GC) are rarely used being off-line, time-consuming, and expensive. Here, we explore monitoring the methanol concentration during industrial distillation of cherry, apple, plum, and herb liquor (196 samples) with a low-cost and hand-held detector combining a Pd-doped SnO2 sensor with a packed bed separation column of Tenax TA. Therein, individual methanol concentrations (0.1-1.25 vol % or 153-3266 g methanol per hectoliter of pure ethanol) are quantified rapidly (within 2 min), bias-free and with high precision (i.e., 0.082 vol %) by headspace analysis, as confirmed by GC. Most importantly, methanol levels above E.U. and U.S. legal limits were recognized reliably without interference by much higher ethanol contents (5-90 vol %) and aromas. Also, the detector worked well even with viscous and inhomogeneous mash samples containing fruit pulp. As a result, this device can help consumers, legal authorities, and distillers to check product safety, guide distillation, and monitor even fermentation to possibly prevent occupational methanol exposure.