WINE COMPOSITION, RESEARCH INTO

Bacchus to the future’, The Economist Technology Quarterly Nov 30th 2013, p20

‘Another avenue of research involves analysing the thousands of different chemical compounds found in red wine, to determine how its composition affects the way humans perceive it. These compounds can be separated and analysed using a technique called gas chromatography-mass spectrometry. Many of the compounds in wine have never been catalogued, and even among those that have, subtle differences in structure can lead to big differences in humans’ sensory reactions. Characterising them fully requires nuclear-magnetic resonance spectroscopy, a technique in which the isolated substances are placed in a magnetic field, and their absorption of radiation is measured at different points. “It’s like a puzzle,” says Axel Marchal of the Institute of Vine and Wine Sciences (ISVV) in Bordeaux. The ISVV’s spectrometers are custom-built, with slots carved out for researchers’ noses so they can smell each compound separately. This technique has led to successes in the past: it was used to identify thiols as the source of the signature passion fruit aroma in sauvignon blanc, and methoxypyrazines as the cause of bell-pepper smells in cabernet sauvignon. Further research showed that pruning leaves at the bottom of the vine sharply reduces methoxypyrazine concentration, one reason why Bordeaux reds taste far less “green” than they once did. Unfortunately, most aromas are not that simple. They are often produced not by individual compounds but by combinations of chemicals, including some that are odourless but modify the effect of others on nerve receptors. “The human nose is a very powerful detector,” says Mr Marchal. “It’s much more powerful than mass spectrometry.” The grape genome was sequenced in 2007, and scientists are optimistic that they will begin to unmask the relationships between terroir, vine, wine and perception in the coming years.’