Sauvignon blanc 2011: Oxydation in white wines, waging war on sotolons

Oxidation in white wines – waging war on sotolons

In addition to two mornings of tastings, the event delivered valuable additional content to participants. As an introduction to the competition itself, Concours Mondial du Sauvignon patron Professor Denis Dubourdieu moderated a conference devoted to ageing problems and oxidation in white wines. Premature oxidation is by no means inevitable and Professor Dubordieu’s team have been studying the issue for several years. Outlining the key role played by glutathiones – tripeptides with well-known redox properties – Dubordieu described in detail their highly protective action against premature ageing faults in wines. These range from what Dubordieu describes as loss of fruit, to honeyed or even mothball aromas, wine colour evolution and the absence of reductive bouquet.

Which options are available to safeguard the effect of glutathiones and delay the inevitable onset of oxidation and sotolons, the lactones which promote the development of oxidised aromas in wines such as Sherry ? Research by Professor Dubordieu and his team has shown that ageing on the lees can be highly effective, provided two elementary rules are followed, namely avoiding new oak and keeping the lees in the wine. “In new barrels without lees, the wine is premox (prematurely oxidised, Ed.) before it leaves the barrel,” summarises Dubordieu.

Keeping the lees is essential because they release glutathiones, are highly reductive and fix oxygen for wine, protecting it from oxidation and the faults it causes. The presence and incorporation of oxygen into wine is vital. Experiments clearly show a correlation between dissolved oxygen and premox characteristics in wine. There is a similar correlation between oxygen levels and wine colour evolution as well as high sotolon content.

Dubordieu’s research work allows him to formulate a number of recommendations that begin in the vineyard. One is that white vines need to be sufficiently robust. Unlike red vines, weaknesses in white vines – caused by water stress or under-nourishment -  reduce aroma precursors. Phenol extractions must also be restricted and short fermentations preferred as fermentation causes loss of glutathione, or what Dubordieu has dubbed “the elixir of life”. Ageing methods also hold the key – large oak containers are preferable to new barrels and the wine should be kept on the lees. The risk of oxidation during bottling should similarly be kept to a minimum and choice of closure carefully thought through. The issue of closures is a hot potato and one which Professor Dubordieu chose not to dwell upon, preferring instead to simply stress the basic precept that wine is about balance between oxidation and reduction.