For Kirsten Skogerson at the University of California, Davis, wondering about how chemical composition affects the flavour and body of a wine took her from a degree in viticulture and enology into metabolomics research. When Skogerson arrived in Oliver Fiehn's lab as a postgrad she looked for a project that would marry Fiehn's expertise in metabolomics and her interest in wine.

“There are so many questions in wine science that you could start to answer by doing a global analysis,” she says. A deeper understanding of the biochemistry of grape-juice fermentation could help the winemaking industry by complementing the arts of the traditional wine taster. So Skogerson and Fiehn set out to survey wine 'metabolomes', in search of key chemical components contributing to body.

Credit: G. WOHLGEMUTH

Using proton nuclear magnetic resonance (NMR) and gas chromatography–mass spectrometry (GC–MS), they looked at 17 different white wines with a wide range of body. For GC–MS analysis, they first removed the alcohol under reduced pressure and then ran samples on a LECO Pegasus IV GC TOF MS system and analysed the spectra using the BinBase program developed in Fiehn's lab. Each wine was also directly analysed on a Bruker Daltonics 600 mHZ NMR instrument with the resulting peaks being compared to the commercially available Chenomx NMR database for metabolite identification. “When you think about it, you have the grape metabolome being acted on by the yeast, plus the added complexity from the yeast metabolome, so the metabolite profile of a wine is very complex,” says Skogerson.

They found a total of 413 metabolites among the wines — probably only a small fraction of the wine metabolome — of which 108 could be positively identified. And in both data sets, the amino acid proline showed a positive correlation with body as assessed by trained wine tasters. How proline relates to body is not yet clear, however. “That is the hard part of being in metabolomics — you get clues, but the follow-up is the real challenge,” says Skogerson. Still, she thinks proline could be used as marker for a wine's viscosity.

Red-wine drinkers have not been forgotten. Bruker Daltonics in Billerica, Maryland, has profiled red wines for important polyphenolic secondary metabolites such as tannins, flavonoids and anthocyanins. This demonstration used the Acquity ultra-performance liquid chromatography system from Waters to separate red wine metabolites for analysis by Bruker's LC-ESI QTOF MS instrument as well as analysis by NMR coupled with Bruker's BioSpin Spectral Base analysis package.

Does knowing the chemistry behind that wonderful bottle of wine take away from the pleasure? Not according to Skogerson. “Science has the potential to bring the art of winemaking to a higher level.”

N.B.