Structurability: A collective measure of the structural differences in vodkas

Although vodka is a reasonably pure mixture of alcohol and water, beverage drinks typically show differences in appeal among brands. The question immediately arises as to the molecular basis, if any, of vodka taste perception. This study shows that commercial vodkas differ measurably from ethanol-water solutions. Specifically, differences in hydrogen-bonding strength among vodkas are observed by ¹H NMR, FT-IR, and Raman spectroscopy. Component analysis of the FT-IR and Raman data reveals a water-rich hydrate of composition Ė(5.3 ± 0.1)H₂O prevalent in both vodka and water-ethanol solutions. This composition is close to that of a clathrate-hydrate observed at low temperature, implying a cage-like morphology. A structurability parameter (SP) is defined by the concentration of the Ė(5.3 ± 0.1)H₂O hydrate compared to pure ethanol-water at the same alcohol content. SP thus measures the deviation of vodka from "clean" ethanol-water solutions. SP quantifies the effect of a variety of trace compounds present in vodka. It is argued that the hydrate structure Ė (5.3 ± 0.1)H₂O and its content are related to the perception of vodka.