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Thursday 23 October 2014

Fermentation key to premox battle

26th September, 2013 by Gabriel Stone

International consultant Professor Denis Dubourdieu detailed the fight against oxidation as he joined Julian Chivite to show nearly two decades of the Navarra producer’s Chardonnay.

(l-r) Valérie Lavigne, Denis Dubourdieu and Julian Chivite

(l-r) Valérie Lavigne, Denis Dubourdieu and Julian Chivite

Although this variety accounts for just 3% of the Spanish region’s total vineyard plantings, Dubourdieu maintained Chardonnay’s superiority over Navarra’s Viura, Garnacha Blanc or Malvasia for the production of age worthy wines.

“If you want white wine to age, then your options are very limited,” he argued, dismissing Viura as “an everyday wine.” As for some of Spain’s most famous mature white wines such as Lopez de Heredia Viña Gravonia or Marqués de Murrieta, Dubourdieu simply remarked: “They are oxidised.”

Instead he outlined his own approach at Chivite, where the Chardonnay grapes are pressed at a low temperature and fermentation “is fast and complete within two weeks.”

This emphasis on ensuring quick fermentation was raised again by Dubourdieu’s colleague Dr Valérie Lavigne from the Faculty of Oenology at the Bordeaux Institute of Vineyard and Wine Sciences. She attributed this factor in particular to the premature oxidation issues faced in recent years by white Burgundy.

Summarising her own detailed research into the causes of “premox,” Lavigne listed seven key moments in the winemaking process when grapes can become especially susceptible to oxidation.

In the vineyard, she noted how a lack of nitrogen diminishes plant vigour and therefore the levels of glutathione in grapes, a compound which protects against oxidation.

Once grapes have been picked, Lavigne recommended limiting the extraction of phenolic compounds during pressing on the ground that excessive levels will also lower the amount of glutathione – a highly reactive compound – in the juice.

Thirdly, she noted: “It is very important to protect the wine with inert gas and sulphur dioxide,” insisting: “it is not possible to produce wines that will age without sulphur dioxide.”

During fermentation, Lavigne stressed: “the must should not be too clean or fermentation will be too slow or incomplete and if so it will lose its reductive qualities and the evolution will be too quick.”

Likewise, she emphasised the importance of ensuring only a short period elapses between alcoholic and malolactic fermentation, noting: “at this time the wine is not protected against oxidation” as there is not yet the protection offered by sulphur dioxide.

Highlighting a particular link between white Burgundy’s problems and the fermentation stage, Lavigne noted the region’s widespread introduction of pneumatic presses during the mid-1990s. By failing to adapt their pressing to this more efficient technology, she argued: “the juice was too clear and the fermentation too slow – but most people don’t want to recognise that.”

While battonage has taken some of the blame in certain quarters of Burgundy for encouraging oxidation, Lavigne argued that, by contrast, this technique helps to create a more reductive atmosphere. “In Burgundy they don’t stir the lees so the wine has no protection at a stage when it is very sensitive,” she observed.

Moving on to the final stages of production, Lavigne highlighted the importance of limiting the wine’s exposure to oxygen during bottling. As for the extent to which closures are responsible for premox, she remarked: “It is easy to blame but it is only a small part of the problem.”

Summing up this detailed understanding of the causes of oxidation, Dubourdieu remarked: “Nowadays this knowledge is easy to get but surprisingly people do the same things and try to ignore the solution that has been proposed – but that’s very common in human nature. Many people complain about the effects but like the causes.”

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