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Published:  23 July, 2008

Reverse osmosis, spinning cones and micro-oxygenation are three winemaking techniques in greater use than the wine trade would like to admit. How do these practices affect wine, and is the controversy surrounding their use just another stick with which to beat interventionist winemakers? Jamie Goode investigates

Clark Smith is a controversial figure. He comes across as articulate, shrewd and at times very funny. But while to some he's an inspired innovator, to others he's the devil incarnate. Why? Because his company, Vinovation, is the leading pioneer of a technique known as reverse osmosis, which increasingly is being used worldwide as the latest high-tech tool in the winemaker's arsenal. To traditionalists, these machines represent a very real threat to the soul' of wine itself. A key concept underlying Smith's work is that a grape's phenolic maturity is independent from sugar levels. That is, while grape sugar accumulation and acid respiration are highly dependent on the climate, the colour, aroma synthesis and tannin evolution occur at more or less the same rate wherever grapes are grown. This means that in warm regions the big problem is that the rapid accumulation of sugars can impose a premature harvest, even though the grapes have not reached phenolic maturity. The traditional compromise has been that if you want to pick grapes at optimum flavour maturity then you have to tolerate alcohol levels that are often excessively high, and in many cases are to the detriment of wine quality. In cooler climates the problem is quite different: achieving phenolic ripeness often means leaving grapes to hang well into the onset of the autumn rains, risking dilution. Vinovation's reverse osmosis technology offers solutions to both problems. Too much alcohol? You can remove it from the finished wine. And if your grapes have been rained on, you can concentrate the must before fermentation. So how widespread is the use of these techniques, and are they compatible with fine wine production?

How it works You might remember the principle of osmosis from school science lessons. If pure water and wine at the same pressure are separated by a semi-permeable membrane, water will flow across the membrane from the pure water side (more concentrated in water) to the wine side (less concentrated in water). This is not what you want, of course, for the must or finished wine would become more dilute. The answer, or at least part of it, is to increase the pressure on the wine side, which then reverses the flow. It's not quite as simple as this, though. As the pore size of the filter membrane decreases to the levels needed for wine applications, dissolved molecules begin to foul it, making it unusable. The key to the success of reverse osmosis is the use of what is known as tangential, or cross-flow, filtration: instead of the flow being pushed through the filter, the process mimics the blood capillaries in the kidney by directing the flow across the filter. As a consequence, the turbulent fluid flow keeps the filter clean. Yes, a lot of energy is wasted in protecting this membrane from getting clogged up, but it works. There are currently three key uses for this technique: removing water from grape must, and removing alcohol or volatile acidity from a finished wine.

Alcohol reduction If you grow grapes in hot climates - as in most New World regions - usually you have to make a compromise with the time of harvest. Pick too soon and you'll have ideal sugar levels and poor phenolic ripeness. Wait for optimum phenolic ripeness (flavour maturity) and the danger is that the sugar levels will be so high that you'll end up with overly alcoholic wines. Not to worry, though. Vinovation can take some of your wine and run it through a reverse osmosis machine. This will remove a colourless, flavourless permeate that consists of water, alcohol and an undissociated form of acetic acid. The important stuff remains in what is known in the trade as the retentate. Vinovation will then distil the alcohol off and add the water back to create lower-alcohol wine that can then be used as a blending component, to mix back with the untreated wine to create a series of test wines at different alcohol levels, ideally separated by 0.1% increments. The next stage is tasting these samples to pick out the wines that taste the best. These points of balance are known as the sweet spots'. We never see a normal distribution of preference,' Smith says. It's like the tuning of a chord.' Sweet spot determination is nicely illustrated by a fascinating collaborative project between Vinovation and California State University in Fresno. In 1999 the oenology students made a wine from Central Valley Syrah grapes. A quarter of this wine, which weighed in at a heady 18% ABV, was sent to Vinovation, which reduced the alcohol level to 10.1% by reverse osmosis. Using this as a blending component, trial wines were made at 0.1% alcohol increments, from the control of 18% down to 12.8%. A panel of 22 judges assessed these wines and came up with four points of harmonious balance', at 13.35, 13.75, 14.35 and 15% alcohol. These wines were then sold commercially in a pack of five (the four sweet spot wines, plus the original 18% wine). I've not tasted them myself, but I've heard two independent reports from people who have, and who were quite impressed. In addition, I've seen a brief summary of unpublished results from a laboratory analysis of these five wines carried out by Professor Donato Lanati from the University of Turin (and of the Enosis wine consulting company), which suggests that while the wines are almost identical in terms of anthocyanins, polyphenols and acids, the reduced alcohol wines might lack some low molecular weight terpenoids that help with aroma development in bottle ageing. Clearly, more independent work is called for here, a sentiment shared by Roger Boulton, Professor of Enology and Chemical Engineering at the University of California, Davis: There are no independent published reports of the sensory effects of this treatment compared to a control,' says Boulton, only proprietary claims and selective testimonials. There is no published example of a side-by-side comparison across several wines.' An alternative technique for alcohol reduction is the spinning cone column. Quite different in principle, this separates out different volatile fractions from the wine by means of centrifugal force and vacuum, which are then blended back once the alcohol has been removed. ConeTech is the US company behind this technology, which is now being exported. While these sorts of manipulations may sound horribly interventionist and the stuff of science fiction, they are becoming quite common in California. I asked Smith how many wineries use either reverse osmosis or ConeTech's spinning cones for alcohol reduction: We each have 300 clients, with some overlap. I'm guessing about 500 wineries, which is about half the state. We're just beginning in Australia and South Africa,' he adds. Interestingly, while Smith is not in a position to name names, he says that it is mostly high-end wineries that are showing an interest. It's the only way to get consistent phenolic maturity and true harmonious balance,' he says. Must concentration Reverse osmosis (or RO) has also found a home in the classic regions of Europe. Here, the problem is that harvest often coincides with the onset of rainy autumnal weather. If it rains during harvest, you can end up with a dilute wine, and many potentially good vintages are ruined this way. Smith explains, In Bordeaux, true ripeness often means hanging into the rain, and an RO can squeeze this rain back out, so we can obtain flavour concentration and alcohol balance.' He points out that the widely used traditional' technique of chaptalisation ignores this dilution and corrects just the alcohol imbalance with added sugar. One problem with using RO for must concentration is that it requires clarified juice, so the smaller the amount to be concentrated the better. A modern RO machine operating at 1,500 pounds per square inch (psi) can concentrate a portion of the must to 42 brix (higher than would be required for German TBA), which can then be used for blending. An alternative method of removing water from the must is by means of vacuum distillation. These concentrators heat the must to temperatures of around 25-30C under vacuum, and can treat from 10-80 hectolitres (hl) of must per hour, with an evaporation capacity of 150-1,200 litres per hour. These machines have been popular in the past, and their use preceded that of reverse osmosis. However, they have drawbacks. The heating of the must can introduce aroma losses and a butterscotch character to the fruit, and they are much more expensive than today's reverse osmosis machines. In principle, the use of reverse osmosis or vacuum distillation to remove excess water from the must is simply a correction of a vintage anomaly, with the winemaker removing only the rainwater that otherwise would have caused a diluted wine. But the problem is that in a market dominated by critics who award high scores to super-concentrated wines, the temptation to do a little more than remove just the rainwater is very strong. Too strong, in fact, for the cellarmasters of many of the leading Bordeaux properties to resist. Must concentration by reverse osmosis or vacuum distillation is allowed within the EU, but the regulations limit its use to a 20% maximum volume decrease and a 2% volume maximum potential alcohol increase. It's illegal to chaptalise and concentrate the same batch of wine. Still, even within these limits, it is possible to make a super-concentrated wine that some critics may have trouble differentiating from one produced by the more traditional formula of low yields, good vineyard sites and careful fruit selection. How widespread is must concentration? It's hard to get an accurate picture, because companies who supply these services are unwilling to name names, and most properties who own machines don't tend to boast about it. I've spoken to quite a few people, and the only clear answer I can get is more than you might think'. James Lawther MW, an expert commentator on the Bordeaux scene, believes there are over 60 reverse osmosis machines in operation in the region, and about as many vacuum concentrators again. Then there are a number of contract companies who offer RO, all of whom are pretty busy at harvest time. Must concentration is also being practised in Burgundy, but on a much smaller scale. Elsewhere in Europe, the picture is one of a technical revolution in the offing. In Germany, more than one hundred wineries have experimented with must concentration, mainly in Baden and the southern areas. In Italy there are reverse osmosis machines in Piedmont, Tuscany and Alto-Adige. It seems that things are just underway in Spain, although reverse osmosis doesn't appear to have reached Portugal.

Micro-oxygenation Another high-tech manipulation that is currently the focus of much attention is micro-oxygenation (or microbullage, as it is sometimes known). The principle behind it is quite simple: it's a winemaking technique for adding very low levels of oxygen to a developing wine over an extended period. The idea is that it allows winemakers to simulate the slow, controlled oxidation that occurs during barrel ageing for wines that are kept in stainless steel tanks. The apparatus involved was developed by a Madiran winemaker, Patrick Ducournau, in the early 1990s. His company, Oenodev, now leads the way in this field. It's a near-miraculous technique, if its proponents are to be believed. Among other things, micro-oxygenation is supposed to build structure, reduce herbaceous or vegetal characters, provide colour stability, stabilise reductive qualities and increase the suppleness or roundedness of the wine. Robert Paul, of Wine Network Consulting in Australia, a company providing micro-oxygenation facilities to around 30 wineries, claims that treated wines can gain a more savoury, structured palate'. Randall Grahm, of Bonny Doon in California, is an enthusiastic supporter of micro-oxygenation. He asserts that microbullage, if practised appropriately, is the most useful tool for the mastery of levage'. However, there are conflicting ideas about what micro-oxygenation actually achieves. A popular notion is that it makes red wines drink well earlier. This is based largely on the huge commercial success of the branded wines from Rosemount, which has been attributed in part to micro-oxygenation allowing them to come to market in the same year as production. Paul says that, The technique is very successful, but the hardest part is convincing people that it is not about softening wines to make them drinkable earlier'. Apparently, it's a bit of a paradox. According to Paul, The treated wines are more apparently rounded: I would argue that this is because they are better wines fundamentally - they have better balance, stability and structure and are cleaner, with more apparent fruit.' On a recent trip to Portugal I mentioned to winemaker David Baverstock that I was writing about micro-oxygenation. He suddenly became quite animated; he's clearly excited by this technology. We're doing quite a bit of micro-oxygenation in the Alentejo, particularly with Monte Velho,' he said. Baverstock claims that it gets rid of a lot of the green tannins and softens up the wines. He tends to use this technique with the more commercial wines, and has employed it at Quinta de la Rosa in the Douro, with the estate's second wine. There's always some fruit that is never quite as good as the top stuff, perhaps from younger vineyards or from less well-controlled growers.' He uses micro-oxygenation in conjunction with different sorts of oak chips, matched to the type of the wine. There seem to be two common motivations for the use of micro-oxygenation. First, it is a useful remedial technique for removing unwanted green characters or sulphides from red wines. Second, there's a cost saving: instead of using expensive barrels for mid-range wines, it's possible to produce the same effects with micro-oxygenation, in combination with barrel staves or oak chips in tank. But for all the scientific claims made by its proponents, micro-oxygenation is still a bit of a black art, based on trial and error rather than precise knowledge of the underlying mechanisms. Boulton expresses some reservations in this regard. The chemical effects are likely to be numerous, but there are no independent scientific measurements of the changes - mostly supplier claims and selected satisfied testimonials.' He continues, There is little indication that the proponents of this treatment have developed a strong understanding of the changes occurring and there are both short-term and longer-term results that cannot be predicted. In terms of science, treatments that are shrouded in secrecy, selective results and "proprietary" methods will have little scientific acceptance until they can be independently reproduced and validated. There is little evidence that "micro-oxygenation" has come close to a scientific method and it seems that some people prefer it that way. Please note,' he adds, that in terms of oxygen consumed and acetaldehyde produced, it is multiples of what most wines ever see during barrel ageing, even when racked frequently, so the term "micro-oxygenation" is something of a misnomer.'

Is it a sin? Let's get philosophical. A crucial question regarding these three winemaking interventions - alcohol reduction, must concentration and micro-oxygenation - is whether they are appropriate or honest manipulations for making quality wines. In other words, is it cheating? As Smith puts it, The central debate about reverse osmosis and other high-tech wine production innovations is no longer about whether they work; it is about whether we will go to hell if we use them. That they work is taken more or less for granted,' he says, in the same way that procreative ability is a side issue in assessing one's daughter's suitors.' Grahm makes an important point here. He thinks it's a question of context: If a producer produces a vin d'appellation, there is an implicit contract that he enters into, whereby he effectively promises a wine of some degree of typicity, which I suppose would include the characteristics of the vintage. If he utilises certain techniques in the winemaking process to wipe out vintage characteristics, even though he is perhaps producing a wine that most punters would prefer, I believe that he is acting in bad faith. If he is producing a vin de table, vino da tavola or a wine in the New World,' adds Grahm, I think that a different set of criteria apply. His contract is simply with the consumer to make the best wine that he can and that will offer the consumer vinous jouissance.' I tend to agree, in that I'm much more comfortable with the idea of alcohol reduction in New World wines than the use of must concentration in wines from the classic European regions. As Grahm puts it, There are some great old vine vineyards in the New World that were planted in areas that are perhaps too warm for the grapes to arrive at optimal flavour/alcohol balance. One makes a better wine picking them riper and taking a little alcohol out of them than by picking them earlier.' Others are less accepting. When I quizzed Ernst Loosen of the Mosel about the increased use of must concentrators in European wine regions, he was quite clear: In my opinion it's an awful development. How far can we go before wine becomes artificial?' Increasingly, he says, as machines are taking over, wines are losing their individuality. It's already getting boring, with all these over-extracted wines that lack any edges.' Perhaps more important than the issue of technological innovation is the ethos and motivation of the winemakers themselves. If they are passionate people whose goal is to produce the very best wine their terroir permits, then there's little danger that, should they choose to employ them, they will use techniques such as these irresponsibly. In the meantime, open discussion of these technical issues can only be a good thing. Consumers need to be kept informed, so they can participate in the debate about how much intervention' they would like in the wines that they are purchasing. And Smith is quite critical of wine writers, who he thinks have failed to educate consumers properly about the role technology has to play in winemaking. There's a major disconnect between what's being done to improve wine quality and what wine writers choose to let consumers look at. The idea is that they are protecting the notion of wine: they feel it is so fragile that if we tell people what is really going on, then the mystery will go away.'