bubble test is a visual method for calculating the percentage of alcohol in a distilled spirit by shaking the solution and evaluating the size of the resulting bubbles. A distilled spirit is a combination primarily of ethanol and water. Due to their molecular structure and polarity, water molecules tend to congregate, thereby creating strong surface tension. Ethanol has similar tendencies but to a lesser degree and thus has a lesser surface tension. This allows the two substances to mix but with variable surface tension depending upon the concentration of alcohol in the solution. As the alcohol concentration rises in an ethanol/water solution, the surface tension drops. When this is agitated, larger bubbles form. Although many factors such as temperatures and additives can alter the results, an experienced analyst can determine alcohol percentage by volume through the size of the bubbles.
moonshine. American folk distillers may refer to the bubbles as frog’s eyes or goose eggs. Today, mezcal producers throughout Mexico still use the bubble test as the method for determining proof. Using a venencia, an approximately 50-centimeter-long piece of the native plant carrizo that has been dried and fashioned into a pipette, the mezcalero will pull the mezcal into the pipette using his breath. The mezcal will then stream through the narrow opening of the venencia into a dried, hollowed out gourd to create las perlas, or the pearls, on the fluid’s surface for evaluation. See mezcal.Smith, George. A Compleat Body of Distilling, Explaining the Mysteries of That Science, in a Most Easy and Familiar Manner; Containing an Exact and Accurate Method … 2 vols. London: 1738.
By: Misty Kalkofen