Are the premature oxidation woes that beset white Burgundies from the mid-1990s now threatening red wines? A study now casts doubt on the longevity of super-ripe, oaky, low-acid reds. Jane Anson reports...

Exotic scents of prunes and figs, the burnt toast undertones of barrel ageing, the silky mouthfeel and unmistakable heat of high alcohol. Before you decide whether this sounds appealing or not, consider that these signs of a sunshine-filled wine from a hot vintage might just also be indications of a wine crisis hiding in plain sight.

There were plenty of rumblings about this at a recent 10-years-on tasting of Bordeaux classed growths from the 2003 vintage. Even among the biggest names there were bottles that were showing tired fruit, flabby structure and were generally past their prime; all signs of oxidative destruction that is not expected at such an early stage in the life cycle of fine red wine. Granted, 2003 was an unusual vintage – the result of a heat spike across Europe that has not (quite) been repeated since. Even at the time, some critics warned that these wines would not age well. But does the irrefutable proof of that, 10 years on, point to a bigger elephant in the room?

There are some experts who believe so. ‘We are used to identifying premature oxidation in the delicate aromas and colours of white wine, but when it was first discovered, nobody wanted to talk about it,’ says Denis Dubourdieu, professor at the Institute of Oenology (IS VV) in Bordeaux and one of the team who led a groundbreaking study into premox in white wine in the early 2000s.

‘I believe there is a similar scandal with red wine, and that in 10 years’ time it will be just as explosive as the one affecting white Burgundy has been. And it’s not limited to one region; all red wines that are expected to be aged for long periods of time – so Barolo, Napa, Bordeaux, the Rhône, Burgundy and others – are in danger of ignoring this threat.’

These wines are at the epicentre of the fine wine trade, explaining why the very idea – whisper it – that premature oxidation might not be limited to white wine is so explosive. I first wrote about the subject for Decanter.com last year and quickly realised that the findings throw into doubt not only the leading viticultural practices of the past decade, but also the work of several leading critics who have amply rewarded low acidity and super-ripe fruit; two of the leading offenders for rapid ageing.

Storing up trouble

At first, this seems like an unlikely problem. Red wines have greater natural protection against premox than whites – the tannins and phenolics in the grape skins are natural buffers against oxygen, and the composition overall of red wines makes them less fragile than whites. The issue is further complicated by the fact that premature ageing is not an issue that you discover immediately. It takes years to see how fine red wine is developing, and most bottles are left in cellars for at least a decade before consumers start opening them.

‘But I have seen issues with a number of expensive, classified wines that are potentially storing up trouble for later,’ warned Dubourdieu as I caught up with him for an update this month. ‘Unfortunately the research takes a long time and while we are finding out more and more about the potential issues, some producers are continuing to produce new vintages that are not going to age as well as they should.’

Dubourdieu points to the 2003 vintage as the most obvious example, although in that particular year there were other issues such as a lack of phenolic ripeness because some vines completely shut down in the heat.

More generally, any very warm vintages – such as 2009 in Bordeaux, or 2013 in Napa – could be at risk. And it’s not just early ageing that is a problem, but the fact that overripe grapes mask terroir, so varietal and regional characteristics are lost. The team at the ISVV has issued a research document on the problem – so is anyone taking it seriously? What should we be looking for? How has it even happened? And what can we as consumers do to protect ourselves?

‘The causes are in most cases entirely avoidable,’ says Dubourdieu’s fellow researcher Valérie Lavigne. ‘There are two principal risk factors: firstly, leaving the grapes on the vines until they are overripe; and secondly allowing too much oxygen during the winemaking process. Using low doses of sulphur dioxide (SO2), particularly when coupled with a high pH (pH is connected to acidity levels in wine, which drop as fruit ripens, and beyond a pH of 4, SO2 loses almost all of its protective effect), is another danger, as is excessive use of new oak, which is highly oxygen-hungry’.

Warning signs

The push towards riper fruit began in earnest in the 1990s – and by and large has brought about hugely positive results. Before then, green harvesting was rare, yields were higher, alcohol lower and picking earlier. Unripe flavours in the resulting wines were fairly common. But slowly, as winemakers began to look for extraction and concentration, the viticultural and vinification techniques changed – more vigorous extraction on higher-sugar grapes, leading to higher-alcohol, lower-acid wines. Similar trends were seen both in Napa Cabernets and the garagiste movement in Bordeaux, particularly with the Merlot grape, with similar results; namely high alcohol, high oak, high tannins, and a pH straying dangerously close to 4.

Tod Mostero, winemaker at the Moueix-owned (and classically farmed) Dominus Estate in Napa, has witnessed the problem. ‘Many compounds contribute to the oxidation (premature or otherwise) of wine. Procyanidins, one of the many types of phenolic compound, are well-known for ‘protecting’ anthocyanins, the colour in wine. Since the concentration of phenolic compounds generally increases during the first part of ripening, then decreases during the last part, overripe fruit can lack certain protective compounds, leading to more rapid oxidation. A high concentration of sugar (and therefore potential alcohol) in overripe fruit may also be a factor that influences oxidation’.

‘But overripe fruit is not the only factor involved,’ says Mostero. ‘I have noticed that many of those who prefer very ripe fruit also prefer to use a lot of oxygen during vinification to make the wine fruity and approachable early on, but it may tend to tire out earlier as well.’

The warning signs of premox in reds are in the appearance of certain aroma markers, even in very young wines, such as prunes, stewed fruits and dried figs, and this is often linked to a rapid evolution in colour. Dubourdieu, and Lavigne have found two specific molecules – ZO1 giving the prune aroma and ZO2 giving a stewed fruit smell – that develop rapidly in the presence of oxygen.

Ripe for discussion

Not everyone agrees that this is a widespread issue. Dany Rolland, the wife and laboratory partner of wine consultant Michel Rolland, has been a vocal campaigner for riper fruit, and says that any issues are easily manageable with correct winemaking.

‘We have seen premox in whites, certainly, but have not found issues with reds. We are used to working with very ripe fruit in Pomerol, St-Emilion, Argentina and California, but we simply protect the fruit and ensure stable conditions throughout the winemaking process. For Christmas 2012, we drank a double magnum of the 1989 vintage from one of the first Argentinian wines we ever made. It had 16% alcohol and a pH of around 4, but it was drinking perfectly and was young and fresh.

‘Perhaps certain organic wines that work with very low doses of sulphur have the potential of developing unwanted issues such as brettonamyces, but not necessarily early oxidation. And even here if you work carefully with inert gas it is perfectly possible to allow them to age without worrying about the risks.’

Michel Rolland himself points to the influence of acidity.‘Great reds tend to stay at below 3.8pH. This will always help with their ability to age. Even on Bordeaux’s Right Bank, the best soils and terroirs have that ability to retain acidity even with very ripe fruit and in very hot vintages. But ensuring a good pH is open to everyone, and can be achieved by ensuring the vineyards are well looked after, with no over-fertilising and a good root system.

Proving this point, I recently attended a vertical of Pomerol’s Eglise-Clinet with Michel and Dany Rolland, where the levels of alcohol ran from 12.5% in the 1990s to 14.5% in 2009 and 2010. There was no hint of oxidation in any of them – but what was remarkable was that the pH was nearly always the same (between 3.6 and 3.75) regardless of the alcohol level. Owner Denis Durantou ascribed this to the work he did in the field, and the ‘old vines, with deep roots, along with the cool clay soils’.

‘The problem is that many of us have become intolerant of acidity in wine,’ says Lavigne. ‘So winemakers do all they can to ensure soft, supple and fruity tastes. All of these potential issues come from things that winemakers are doing with the best intentions. Ripe grapes, new oak, low sulphur use – these are all things intended to improve the wine and to benefit the consumer. But it’s important to warn that it’s possible to go too far.

‘So far we have had very little response from the winemaking community to our study, but it took almost a decade for the work we did on premox in whites to be taken up widely, so I am not giving up hope,’ she says.

‘And if consumers start opening bottles that disappoint them, as they did with the whites, then more producers will start to pay attention.’

What is premature oxidation?

Premature oxidation was first discovered in white wines that lost their fruit aromas more quickly than anticipated, developing instead heavier smells such as honey and beeswax, while their colour faded quickly to russet and brown.

Signs of ageing occur in all wines over time, but the accelerated version seen with premox is detrimental when it affects wines that are sold as having great ageing potential – hence the focus on white Burgundy initially, as the expectation for ageing is so high for those wines, so the corresponding disappointment was inevitably acute.

In red wines, the warning signs come with prune, fig and other dried fruit aromas – these are positively sought in specific types of wines such as Amarone or Port, but would be a likely indication in a young dry red that the wine will not age as it should. Some styles of dry reds – such as still Douro reds and some Languedoc wines – naturally have dried fruit aromas when young, and are made from grapes with high natural acidity and resistance to heat. But the danger comes with other grape varieties that are more susceptible to fluctuations in temperature.

The focus of the Bordeaux research so far has been Merlot, as that is the most widely planted variety in Bordeaux, and it suffers in very hot years, but any heat-sensitive grapes are at risk.

Written by Jane Anson