How is Wine Aroma Re-Created Using Gas Chromatography?

Deliciously Scientific - How is Wine Aroma Re-Created Using Gas Chromatography?

An average wine has at least 800 different aroma compounds present in it. The ways in which these react with each other, in which they come to the surface of the wine and in which they are interpreted by the smell receptors in our nostrils determine how a certain wine smells. Analysis of these compounds, in all of its forms, basically involves separating out the compounds for individual identification and analysis. One such technique for doing so is gas chromatography.

What is Gas Chromatography?

At its simplest level, gas chromatography is the process of separating vaporisable compounds into their distinct parts. This is achieved by observing how the various molecules react with specific solvents, and identifying them individually by their varying reactions. These reactions are defined in terms of their “retention time”, which is the time it takes for the molecule to release the solvent. Luckily, each individual molecule has a very specific and unique retention time, which is constant with that type of molecule, but distinct from all others. Using this retention time, scientists are able to identify and separate the various molecules of a compound.

As well as being used in the study of aromas present in wine, gas chromatography has a variety of functions, in fields as varied as forensics, energy analysis, food nutrition, sports testing and even national security. For a closer look at the myriad of functions of gas chromatography, please check out this article.

Gas Chromatography meets Wine

Using this process, scientists have managed to separate out the 800-ish varying compounds contained in wine aroma. Of these 800, only around 10%-20% have as yet been identified and named, but we know the rest exist because of their unique and differing retention times. In a recent study by the Australian Wine Institute, two types of shiraz wine were tested and an attempt was made to synthetically re-create their aroma, using gas chromatography.

Indeed, the process became even more sophisticated with the introduction of gas chromatography-olfactometry, which, through the inclusion of a smelling port on the apparatus, allowed scientists to sniff each compound independently. The research team found that of the 100 aroma-inducing compounds they discovered in the shiraz, only about 50 of those were detectable by the nostril. An even smaller figure, 27 or 28, had been present in the wine in large enough quantities to theoretically make a difference to the aroma. Nevertheless, when trying to reconstruct the aroma, they found that a minimum of 44 compounds were necessary to even come close to replicating the smell.

Pinpointing the Aromatic Culprits

In an attempt to identify which of the compounds affected the smell most strongly, the scientists tried sniffing different cocktails of the compounds, with a different one removed each time. The results were interesting. The team found that removing certain compounds – even ones which were not believed to be key in influencing the aroma – had a profound effect on the final aroma. What this reveals is that contrary to previous belief, not only the molecules which ‘escape’ the wine and react with our smell receptors influence the aroma. Indeed, those molecules which remain in the wine – up until now, believed to be remaining dormant – actually affect how the wine smells as well. The discovery has confused scientists, who now believe more tests are needed. And more wine.