Rapid and mobile determination of alcoholic strength in wine, beer and spirits using a flow-through infrared sensor

During method validation, the precision of the infrared sensor was found to be equal to or better than densimetric or FTIR methods. For example, the average repeatability, as determined in 6 different wine samples, was 0.05% vol and the relative standard deviation was below 0.2%. Accuracy was ensured by analyzing 260 different alcoholic beverages in comparison to densimetric or FTIR results. The correlation was linear over the entire range from alcohol-free beers up to high-proof spirits, and the results were in substantial agreement (R = 0.99981, p < 0.0001, RMSE = 0.279% vol). The applicability of the device was further proven for the analysis of wines during fermentation, and for the determination of unrecorded alcohol (i.e. non-commercial or illicit products).The flow-through infrared device is much easier to handle than typical reference procedures, while time-consuming sample preparation steps such as distillation are not necessary. Therefore, the alcoholic strength can be economically and quickly controlled (requiring less than 60 s per sample). The device also gives the opportunity for mobile on-site control in the context of labelling control of wine, beer and spirits, the process monitoring of fermentations, or the evaluation of unrecorded alcohols.The alcoholic strength expressed in percent by volume (% vol) is one of the oldest parameters for which quantitative analytical methods have been developed, and is still determined in businesses and laboratories around the world. The foundations for the determination of alcoholic strength were laid by Gay-Lussac by inventing not only a simple-to-use centesimal alcoholometer (i.e. a hydrometer with a '% vol' scale) but also by providing the theoretical background in his 1824 monograph 'l'alcoomètre centésimal' [1]. For this reason, the percentage by volume is also called the French or Gay-Lussac system. (American proof is equal to twice the percentage of volume (i.e. spirits that contain 50% vol are 100 proof) [2