Eric Falde, Julia Wang, and Mark Grinstaff* 
*Boston University, 590 Commonwealth Avenue, Boston, MA 02215
(mgrin@bu.edu)

Quantification of alcohol by volume (ABV) in alcoholic beverages is required for commercial sales and is of significant interest for home winemakers. However, the process usually requires large sample volumes, multiple measurements over time, skilled personnel, and/or expensive instruments. Despite the wide variety of compounds in wine (including large differences in Brix between dry and dessert wines), there is a strong correlation between alcohol content and surface tension (R2 = 0.974). Therefore, we report an alternative, instrument-free method of alcohol quantification in wine based on surface tension. A droplet of wine (3 µL) is placed onto the mesh sensor and will remain “beaded up” (>5 min) if the alcohol content is below the rated ABV, but will rapidly (<30 sec) wet into the mesh, causing a color change, if the alcohol content is above the rated ABV. These meshes can resolve down to 0.5% ABV differences in wine, ranging from 12.5 to 16% ABV. The sensors are composed of two layers: a top “responsive” layer and a bottom “indicator” layer. Both layers are fabricated by electrospinning, a well-controlled, robust commercialized manufacturing process. The lower indicator layer, composed of 5% bromocresol purple, 5% poly(glycerol-co-ε-caprolactone), and 90% poly(caprolactone), facilitates wetting and the color change, while the upper responsive layer, composed of 3 to 50% poly(glycerol monostearate-co-ε-caprolactone), selectively allows wetting below a specified surface tension and rated ABV. This facile, affordable, and portable method of accurately determining up to 0.5% differences in ABV within 1 min is sufficient to meet United States labeling standards using only µL samples. 

Funding Support: NSF (DMR-1507081), Mark Grinstaff