AlcoLab: a method for methanol screening using density and syringe-flow measurements, implemented as an open-source application

Methanol adulteration in alcoholic beverages remains a recurrent public health problem. Instrumental methods for detecting methanol are not always available in field settings, while colorimetric methods often require toxic or hazardous reagents. Here we present AlcoLab, a proof-of-concept method for semiquantitative methanol screening in hydroalcoholic mixtures using a balance readable to 0.1 g and a 20-mL disposable syringe fitted with a 22-gauge needle. A ternary viscosity grid was fitted and selected using literature data (46-point model-selection benchmark: MAE ≈ 0.043 mPa·s; MAPE ≈ 2.47%), together with an empirical model linking syringe-flow response to viscosity. Under conditional blocked evaluation over 54 eligible replicates - including 30 measurements in commercial distilled spirits and commercial ethanol, 14 of which were methanol-spiked - the model yielded a MAE of 0.026 for the methanol mass fraction and flagged all 26 methanol-containing replicates, at a 26% false-positive rate over 84 negative predictions. Because the inversion was constrained to a ±2 percentage-point window around the nominal total alcohol content, these figures characterize the flow and inversion stages; all positives contained more than 16% methanol by mass, so performance at low methanol fractions remains to be established. The method is distributed as an open-source progressive web app (alcolab.org; AGPL-3.0) for methanol screening in suspected samples of distilled spirits and commercial ethanol solutions.•Reagent-free methanol screening by density, syringe-flow measurements, and ternary inversion.•Open-source AlcoLab application, with statistical interpretation and traffic-light classification.•Reproducible workflow with a ternary grid, rerunnable scripts, and supplementary videos.