Analytical methods - using GC-MS to assess wine quality
By Geoff Taylor – 21 September 2016
Since I began working in the UK wine industry in 1976, I have tested and advised on tens of thousands of wine samples. The world wine industry is currently going through a very innovative phase at virtually all stages, from grape through to the consumer. This includes using different fermentation techniques and yeast strains as well as different approaches to ageing, wood treatment, transport and storage. All of these factors impact on the flavour and quality of the wine.
We frequently help our clients in the wine industry to identify why a problem has arisen (e.g. a taint, flavour or aroma defect, sediment or haze). Sensory assessments are a valuable tool, but answering questions such as ‘who is responsible’ for an issue requires state-of-the-art science.
Ensuring that wines are at their optimum quality at the point of sale is crucial, especially for those being sold at a higher price or being widely exported. One of the techniques used in the analysis of wines at Campden BRI is Gas Chromatography/Mass Spectrometry (GC/MS).
How does it work?
GC/MS is a powerful technique which separates and identifies key components within the wine down to the nanogram per litre level. Both aroma and flavour compounds are separated and identified in a mass spectrometer with reference to the international mass spectral library. Then, by overlaying chromatographic profiles, changes within a wine can be monitored.
There is also the option of using gas chromatography tandem mass spectrometry (GC/MS/MS), which splits the individual molecules in order to achieve even greater sensitivity and specificity. Time of flight GC/MS (TOF/GC/MS) enables us to detect and identify unknown or unexpected compounds without the need to know what we are looking for in advance.
GC-MS has a range of uses, including identifying taints, looking for migration compounds, investigating different yeast strains, harvest times and fermentation conditions and optimising treatments. The method has proven successful in a number of areas and examples include:
a) A Sauvignon Blanc blended with a cheaper variety. One batch/delivery was much less aromatic and shown to have less Sauvignon Blanc in the blend.
b) An imported wine was tasted on receipt and found to taste tired/old. GC-MS profiles were compared (buying sample verses imported stock) and different compounds, which were markers of heat damage, were detected in the suspect stock.
c) We compared a major branded varietal against its competitors in order to try and identify points of difference. Variables were minimised by using freshly bottled wines from the same vintage at the same point in time.
The potential of profiling wines using GC-MS is significant and, if used correctly, it should be a considerable asset to our developing industry.
To find out more about Campden BRI’s wine quality and troubleshooting services, please contact us.