The idea that the perception of vodka could be influenced by molecular structures within the beverage has been challenged and defended

’Tis the season for the office drinks party, so perhaps an appropriate time for a row to have broken out over the science behind the taste of vodka.

Last May, Chemistry World reported on a paper published in the Journal of Agricultural and Food Chemistry in which a group led by Dale Schaefer of the University of Cincinnati in the US demonstrated that a particular hydrate of ethanol occurred in different concentrations in different vodka brands.1 This hydrate consists of around five molecules of water associated with one of ethanol. The relative amount of hydrate could give different vodka brands a different ’structurability’, the authors suggested, and this in turn could account for people’s preference for one brand over another.

Dirk Lachenmeier, head of the alcohol laboratory at the Chemical and Veterinary Investigation Laboratory in Karlsruhe, Germany, and colleagues Fotis Kanteres and J?rgen Rehm, however, remained far from convinced, and have published a comment on the original paper.2

The authors say that in their work as an ’alcohol control authority’, which involves among other things authenticating brands, it has proved difficult to distinguish between one brand and another purely on taste. ’Even when using advanced approaches combining spectroscopy and chemometrics, it is not often possible to correctly assign the origin of vodka (e.g. between Russia and the rest of Europe),’ they write.

’Probably there are differences in these structures but in my opinion this has nothing to do with the taste,’ Lachenmeier tells Chemistry World. ’I do not think that very small difference would have an influence. I think there is more influence from labelling and branding.’

The team recently carried out tests to see if people could distinguish between vodkas of different alcoholic strength, ranging from 30 per cent to 60 per cent. Only 11 of 24 subjects could discriminate and rank the samples correctly. ’We do not believe there is currently sufficient significant evidence for a taste differentiation of vodka due to structurability or any other effect,’ they conclude.

Schaefer and his coworkers Naiping Hu and Svetlana Patsaeva responded to the attack robustly in a rebuttal published in the journal.3 ’First, we need to clarify our conclusions,’ they say. ’We conclude that vodkas differ in structurability. We hypothesise that structurability is related to perception. Because this is a new idea, ipso facto there is no evidence for taste differentiation due to structurability.’

The blind tasting by Lachenmeier’s group on the perception of alcohol content was ’ill conceived.’ The rebuttal adds, ’To first approximation, structurability is independent of alcohol content, so alcohol-content perception is an inappropriate way to test whether subjects can distinguish structurability.The validity of this hypothesis is still an open question that should not be closed by preconceived ideas or ill-designed experiments.’

Simon Hadlington