IF YOU think plastic corks were an innovation too far, perhaps you’d better stop reading now. Because winemakers have their eye on another technology that will leave traditionalists spluttering into their claret: genetic modification.
All over the world, molecular biologists are tinkering with DNA to find ways to improve the quality of wine. Already they can do wonders, conjuring up rare flavours and aromas, and adding body and complexity to bog-standard plonk. Gene technology can also eliminate the spoilage compounds that can make wine taste like sweaty socks, and even get rid of those nasties that give you a bad head in the morning.
Yet despite the possibilities, you won’t be drinking GM wine this Christmas, or next. “Winemakers don’t want to be associated with gene technology,” says Florian Bauer, a researcher at the Institute for Wine Biotechnology at Stellenbosch University in South Africa.
Advertisement
It is easy to see why. Wine trades heavily on its image as a traditional, artisanal product, and winemakers cling for dear life to their terroir – the alchemic blend of soil, climate and skill that gives wine its mystical qualities. No one wants genetic engineers trampling all over that. Winemakers are also scared stiff of the public. Consumers don’t like the idea of GM products, and it would be a foolish winemaker who tried to force it down their throats.
On the quiet, however, winemakers are very interested in the potential of genetic engineering. Disease-resistant vines, for example, would help in the fight against devastating infections such as Pierce’s disease. But when it comes to quality improvements, only a little attention has focused on the vines themselves. Vines are difficult to engineer and the biological processes that control grape quality are poorly understood.
No, the real star of the show is the other organism involved in winemaking – the yeast. GM yeast has dazzling potential because many of the “organoleptic” qualities of a wine – its colour, aroma and flavour – are down to chemicals spat out by yeast as it munches its way through the mush of crushed grapes. And the metabolic pathways that produce these chemicals have proved obligingly easy to manipulate.
The principal yeast used in winemaking is Saccharomyces cerevisiae, which also happens to be a standard experimental organism in genetics labs. In 1996 it became the first eukaryote to have its genome fully sequenced. Winemaking strains are slightly different from standard lab strains – they tolerate higher levels of sugar and ethanol, grow faster and produce larger amounts of the volatile organic compounds that add flavour to wine. Even so, S. cerevisiae’s long scientific pedigree has helped oenologists enormously.
Already, some research groups have carried out small-scale experimental fermentations using GM yeast. Most do not produce anything that could be described as “wine”, although Bauer for one says he has tasted the fermented grape juice to see whether the yeast is doing what it is supposed to. The results are convincing molecular biologists that they really can manipulate yeasts to take control of the fermentation process.
One success has been to use yeast to correct the balance between sugar and fruit in grapes, which has a huge influence on wine quality. The balance depends mainly on the ripeness of the grapes, which sounds straightforward. But ripeness has two components which rarely coincide: “sugar ripeness”, when the sugar-acid balance is just right, and “phenolic ripeness”, when the grapes are packed with flavour.
Years when these overlap are known as a good vintage, but the rest of the time winemakers have to make a trade-off. In hot climates such as Australia, South Africa and the Mediterranean, sugar ripeness tends to precede phenolic ripeness. And that leaves winemakers with a dilemma. If they harvest when the sugars are just right they miss out on the big fruit flavours. But allow the phenolic ripeness to develop fully and the sugars stack up, so you end up with either a sugary wine or 15 or 16 per cent ethanol. “Nobody wants to drink such heavy wines,” says Bauer. Excess sugar ripeness also causes low acidity, which makes white wines taste flat and uninteresting.
But it turns out that you can easily engineer yeast to deal with the problem. Several research groups, including one led by Sylvie Dequin at INRA, the French agricultural research organisation in Montpellier, have boosted acidity by modifying yeast to produce small amounts of lactic acid using the gene for the hydrogenase enzyme from a lactic acid bacterium. Meanwhile, Miguel de Barros Lopes, a yeast molecular biologist at the Australian Wine Research Institute in Urrbrae, South Australia, has solved the “heaviness” problem by shifting the balance of glucose metabolism away from ethanol and towards glycerol, a desirable compound that gives wine its “body” and can improve the flavour.
Colder regions such as northern France suffer the opposite problem: phenolic ripeness often precedes sugar ripeness, resulting in sour, weak wine. Traditionally, winemakers compensate by carrying out a secondary fermentation, after the alcoholic fermentation. This “malolactic” fermentation uses lactic acid bacteria to convert harsh-tasting malic acid into mild lactic acid. But malolactic fermentation is sometimes difficult to get going, so several research groups, including Dequin’s, have engineered the bacterial genes into yeast so it can carry out malolactic fermentation at the same time as the alcoholic fermentation. According to Bauer, such “malolactic yeasts” do a pretty good job.
Experimental yeasts are also helping to eliminate undesirable compounds. These are the off-flavours that make wines taste sweaty, eggy, gassy or vinegary, the nasties that give you a bad head in the morning, and the carcinogens that get you in the long run. Most off-flavours are developed by unwanted bacteria, moulds and yeasts, so a good deal of effort is going to engineering compounds into wine yeast to kill off spoilage organisms. The Stellenbosch group, for example, has expressed genes for three bactericides and two anti-fungals in yeast.
No more hangovers
That’s also good news on the morning after. “Most wine hangovers are not only due to alcohol,” says Bauer. A big culprit is neurotoxic amines produced by spoilage bacteria. Another is sulphur dioxide, a ubiquitous additive that kills bacteria but can make you feel rough as a badger’s backside in the morning. So commercial yeasts that churn out relatively harmless anti-microbials would be a boon.
Another problem compound is ethyl carbamate, a carcinogen present in all fermented food. This is formed by a spontaneous reaction between ethanol and urea. The urea, in turn, is produced from arginine by the enzyme arginase. As arginine is one of the most abundant amino acids in grapes, wines occasionally exceed the authorised levels of ethyl carbamate. But now it is possible to get rid of the stuff altogether simply by deleting the arginase gene.
Yeast genetics is not just about ironing out problems. It can also optimise the levels of tasty compounds. A prime target is esters, which impart tropical fruit flavours such as melon and pineapple. “They’re very sought after in wines such as Sauvignon blanc and Chenin blanc,” says Bauer. So the Stellenbosch group has made higher than usual amounts of the banana-flavoured ester isoamyl acetate by over-expressing a yeast enzyme.
Other targets include phenolic acids such as vanillic acid and cinnamic acid, and fusel oils, which have a vile, acrid taste but are considered a good thing in small quantities. And the Australian team is looking at volatile thiols, which are produced from sulphur-containing compounds in the grapes. There are two basic types, one which tastes of passion fruit and the other of cat pee. No prizes for guessing which is more desirable – although a trace of cat pee is can actually be considered a good thing. “There’s no such thing as bad substances and good ones,” says Bauer. “Everything is good up to a certain degree.”
All very clever, but is it wanted? Bauer says there is no danger that such alterations will lead to a loss of diversity or regional character. He points out that no amount of tinkering with yeast can alter the wellspring of terroir: the grapes themselves. And altered yeast does not produce standardised results. “You still have to be a good winemaker to make good wine,” Bauer says. “What GM yeast can do is make sure wines at least correspond to certain minimum quality criteria.”
Traditionalists are not so sure. One outspoken critic is Monty Waldin, author of the Organic Wine Guide (HarperCollins, 1999). He sees GM yeast as an extension of an insidious modern craze for “ultra-clean, technically perfect wine” with big fruit, clear fresh flavours – and no character. “It’s phoney wine,” he says. By eliminating uncertainty, GM yeast can ensure a certain minimum standard. But it also leaves less scope for the occasional blend of genius and luck that creates an exceptional wine. That predictability, says Waldin, robs wine of some of its essential charm.
Consumer opposition is also virtually assured, although perhaps there are ways around it. Wine made with GM yeast should not contain any yeast DNA, so it is technically non-GM. That sounds a tendentious argument, but we already consume such products. Most cheese is now made with chymosin, a milk-coagulating enzyme that has replaced calf rennet in all but the most traditional of creameries. Chymosin originated in a fungus, but is now harvested from a bacterium genetically modified to express the fungal protein. Perhaps people don’t object because they don’t know: under European Union rules, for example, the cheese does not have to be labelled because the GM element is a “processing aid”, and no trace of it remains in the final product.
The EU rule also applies to wine. So couldn’t winemakers use GM yeast and just keep quiet about it? Yeast researchers don’t think so. “We cannot say there is no yeast in the wine.” says Dequin. A few cells, albeit dead ones, are likely to remain floating around, especially if the wine is unfiltered. De Barros Lopes believes that even if there were no trace of yeast DNA in the final wine, consumers would still see it as a GM product. In fact every researcher contacted by New Scientist was at pains to point out that no one has any plans to introduce GM products into commercial winemaking.
In any case, winemakers are determined to keep gene technology out of their industry. In June 2000, a group of traditional Burgundy growers formed an alliance called Terre et Vin de Bourgogne and called for a 10-year moratorium on the commercialisation of wine made from GM vines or yeast. Growers in Bordeaux and the Côtes du Rhône quickly threw their hats into the ring. Other regions followed, and Terre et Vin de Bourgogne has now become Terre et Vin du Monde with members across France, Germany, Italy, Spain and the US. Partly in response to their campaign, the Institut National des Appellations d’Origine in Paris has declared that wines made from GM vines will be banned from carrying the prestigious Appellation d’Origine Contrôlée label. Perhaps significantly, however, it has not done the same for wines made with GM yeasts.
But the molecular biologists have a trick up their sleeves that could deliver a genetic revolution through the back door. “Our GM yeasts are just models,” says De Barros Lopes. “Once we understand them, we’ll be able to find the same changes in wine yeasts without using genetic engineering.”
De Barros Lopes’s team of researchers have another technique that could introduce new characters to wine without relying on gene technology. They are experimenting with hybrids between S. cerevisiae and other Saccharomyces species that cannot ferment grape juice on their own but have interesting metabolic qualities. They have already made wine with hybrids between S. cerevisiae and six recently discovered species including S. cariocanus, discovered in 2000 growing on fruit flies in Brazil, and S. mikatae, which normally lives in soil and dead leaves. The outcome, according to De Barros Lopes, is a marked increase in the complexity of the wine – a highly desirable characteristic. Where standard wine yeast produced standard plonk, one hybrid contained complex flavours such as nutty, buttery, soapy, marzipan and earthy.
With such experiments going on, is genetically modifying yeast really such a big step? And in any case, once you look behind the marketing hype it becomes hard to sustain the argument that gene technology will single-handedly put an end to centuries of winemaking tradition. That battle has already been lost. Most wine is already produced in surroundings more akin to a chemical factory than an artisan’s workshop, and most big wineries have all but abandoned traditional methods. Few now rely on the wild yeasts growing on the skin of their grapes. Most buy in bags of dried S. cerevisiae and happily add industrial enzymes to improve the fermentation process, and dump sweeteners or acidifiers into the final product to cover up defects. As a result the market is flooded with identikit wines.
Yet the best wines continue to be made with painstaking care to bring the best out of the grapes. That will always be true. No one wants to see truly artisanal wine production invaded by gene technology. But if GM yeast can add flavour, body and dependability to your everyday plonk, what’s the problem?