Droplets form and slide down the si

Droplets form and slide down the sides of the glass after swirling(Fig. 2.11). These have been variously termed tears," legs," or rivulets.'They form when alcohol evaporates from the film of wine coating the inner surfaces of the glass. Because ethanol volatilizes more rapidly than water, the surface tension of the film increases. This induces water molecules in the film to pull together more tightly, resulting in droplet formation. As their mass increases, the droplets start to sag, producing arches. Finally, the drops slide down, forming the tears. On reaching the surface of the wine, fluidis lost and the drop may pull back. Without repeated swirling, the rim of the film slowly descends, eventually reaching the level of the meniscus around the sides of the glass.
After swirling, the increased surface tension of the film,created by alcohol evaporation, may induce wine to flow upthe sides of the glass (Neogi, 1985). In addition, cooling produced by alcohol evaporation activates the generation of convection currents that facilitate this flow. The duration of tears formation depends on factors affecting the rateof evaporation, such as temperature, alcohol content, andthe liquid/air interface. Movement of wine up the sides ofthe glass can be demonstrated by adding a drop of food coloring, or nonwettable powder such as Lycopodium powder,to wine after tears have begun to form. Contrary to com-mon belief, glycerol neither significantly affects nor is required for formation of tears.