Ever since James Bond, the film secret agent 007, announced that he would like his cocktail martini shaken and not stirred, he started a cult among the young upwardly mobile. Does it make any difference whether you shake the contents with ice or stir them?
Likewise is the debate about single malt whisky. Do you drink it neat, add ice and do so, or can you add water? Is a single malt aged in a casket for 12 years better, or 18 years, or 32 years? A whole field of connoisseurie has emerged out of this. Does it make a difference? Scientists have gotten into this debate and have decided to analyze the solution to find answers.
Unlike whisky, which has other components besides alcohol in it (based on the contents of the wooden caskets in which it is stored), gin or vodka are better choices for the scientific study. This is because they are essentially mixture of ethyl alcohol and water. Even here, it is better to choose vodka for the study, since it has no additives (such as juniper berries used in making gin), and is obtained after four or even five repeated distillations. Vodka is thus essentially an ethanol: water mixture in the proportion of 40:60 (by volume, hence called 80 proof).
Surely there are tiny amounts of other material, contaminants, which stay in the vodka even after all the distillation. But they, namely some oils, salts and such, perhaps make the difference in the “taste” that drinkers seem to detect between brands.
Keeping these in mind, a group of chemists (led by Dr. Dale W. Schafer) in Cincinnati, Ohio, U.S., decided to analyse the properties of as many as five different brands of vodka using spectroscopic techniques. Their results appear in a recent issue of the Journal of Agricultural and Food Chemistry (N.Hu et al. DOI: 10.1021/jf100609c. Structurability: A collective measure of the structural differences in vodkas).
Predictably, the report was covered in the popular magazine The Scientist, and the blogs that followed are worth a read http://blog.the-scientist.com/2010/05/28/one-bourbon-one-scotch/ .
Being essentially a 40/60 mixture of alcohol and water, and Russian in origin, the properties of vodka attracted the attention of Dmitri Mendeleev, the father of the periodic table. He found that the density of alcohol: water mixtures did not vary smoothly as the concentrations changed, but showed bumps at several points; he attributed these to the formation of “hydrate clusters”.
What are hydrate clusters? These are cage-like or multisided box structures made when alcohol and water molecules join hands in a loose manner. The interaction is not through high-energy covalent bonds, but hydrogen bonds which are so weak that heating would make the cluster fall apart.
Not just alcohol, but many other molecules — even inert gases like methane or hydrogen form such hydrate clusters with water, thanks to the ability of water to link with itself, or with other molecules, through hydrogen bonds.
While other polar molecules (such as ethanol) form part of the architecture of the cage, inert ones such as methane or hydrogen are simply boxed inside the hydrate cluster.
Schafer and colleagues decided to study whether vodkas too contain such hydrate structures (also called clathrates), and whether various brands of vodka differ in their clathrate contents. To do so, they used the technique of FT-IR spectroscopy, and compared the FTIR spectra of five different vodkas with those of standard alcohol-water mixtures of known composition. Invariably, all vodkas were seen to answer to the presence of the clathrate (ethanol: 5.3 water). This is a typical clathrate where each ethanol molecule is surrounded by a little more than 5 waters.
These results offered them a method to describe what they term as the structurability parameter or SP. Among the 5 brands of popular vodka, the brand named Stolichnaya had the smallest SP value, while Skyy, Grey Goose, Belvedere and Oval had progressively higher values.
Schaffer asks: “how do vodka drinkers develop brand preference? Our answer is structure. Beverages with low SP are likely to be perceived as watery, because the fraction of water clusters is higher than in brands with high structurability”.
This would mean Stolichnaya would taste watery and Oval robust. Not being an expert, I turned to the web to look up the ratings of various vodka brands, given by those who know. I found that four of the above brands were rated equal by the experts. So, is structurability the only factor? Do the trace ‘contaminants' add to the taste?
And does shaking change the SP differently from stirring the drink? It is hard to say, since the mode of preparation of a material is known, in other instances, to affect its properties. Was James Bond right or just putting you on? I leave it to the readers to judge and let us know.