Water of life
Cheminformatics can be used to process data from headspace mass-spectrometry (HS-MS), mid-infrared (MIR) and UV–Vis spectroscopy and so ascertain the authenticity and origin of Irish, Spanish, Bourbon, Tennessee Whisky and Scotch, according to a study published by researchers from Poland and Spain. Their approach is quick and simple and requires no pre-preparation of samples.
Paulina Wiśniewska, Waldemar Wardencki, Jacek Namieśnik, and Tomasz Dymerski of Gdansk University of Technology and Ricard Boqué, Eva Borràs, and Olga Busto of the Universitat Rovira i Virgili in Tarragona, used collected spectra from five groups of different types of whisky and processed the data with partial least-squares discriminant analysis (PLS-DA) to build a classification model. All groups of whisky could be distinguished from each other but the most obvious differences were seen with the HS-MS, which implies that aroma is perhaps the most important factor in differentiating between whiskies. Nevertheless, differences within groups were also seen which suggests that raw materials used and differences in the actual whisky production process is important too.
Whisky, or whiskey if it is of Irish ancestry, is an alcoholic spirit distilled from grain malted or unmalted. The spirit must be matured for at least three years to qualify as whisky and old water or caramel as a colouring might be added to the authentic product. Of course, there are further subtleties to the nature of this “water of life”: In Europe, for instance, whisky is made from barley malt, water and additive cereals such as wheat or rye and there are different production methods. Scottish and Irish whiskies are produced from similar cereals but Irish whiskey is triple distilled. Spanish whisky, by contrast contains a distillate of maize, like American whisky , which is known as bourbon in some cases.
Given the wide range of whisky types and the value of this spirit, adulteration and fraud are common. Authentication of botanical and geographical origin is paramount in sustaining a legal market in the various products. Conventional one-dimensional gas chromatography and mass spectrometric coupled techniques have usually been the standard when it comes to testing whiskies. But spectroscopy has not, according to Dymerski and colleagues been widely reported in this context in the scientific literature. This is despite the fact that many of those techniques can be seen as analogous to human senses and perhaps more closely associated with the properties of whiskies that we experience, aroma and taste specifically. Spectroscopic techniques are often referred to as artificial noses and artificial tongues when discussing the analysis of food and drink, after all.
The team investigated four analytical techniques (UV–Vis, IR-ATR (infrared-attenuated total reﬂectance), IR-T (infrared-transmission) and HS-MS) combined with partial least-squares discriminant analysis (PLS-DA) to establish a quick and easy method without sample pre-processing to distinguish selected whiskies originating from Scotland, Ireland, Spain and the USA. The team obtained eleven samples of whisky produced in Ireland, Scotland, Spain, Kentucky, and Tennessee from local shops in Gdańsk (Poland) and Tarragona (Spain) to demonstrate their approach and tested each with all four analytical techniques. HS-MS proved itself the most effective in distinguishing between the various products.
The team points out that, “Consumers are increasingly demanding higher requirements for alcoholic products, buying those that appreciate most because of the taste and aroma. Producers trying to meet these requirements create unique recipes designed to attract consumers.” Because of this and the high price afforded higher quality products counterfeit versions abound on the black and grey markets. The team suggests that they must now obtain more samples of different whiskies, and presumably some counterfeit samples too, so that they further validate the technique and define a simple way for quality control and legal authorities to quickly identify counterfeit products with little fuss.