BRETT GENOME UNRAVELLED BY OZ DOCS

THE AUSTRALIAN WINE RESEARCH INSTITUTE TEAM WHICH CRACKED THE BRETT GENOME, L-R: DR PAUL CHAMBERS, DR ANTHONY BORNEMAN, PROF SAKKIE PRETORIUS, AND DR CHRIS CURTIN:

Australia Wine Research Institute
Unravels Brett DNA Architecture
Adelaide Thinks Of Chateau Neuf
by PHILIP WHITE


The Fox, it was called in Adelaide Hills breweries in the ’30s. It eventually killed them. The Wolf. The Old Wet Dog. The Boiler Stoker’s Apron.

Dekkera (Brettanomyces) bruxellensis is a common rogue yeast.

Brett lives in timber and cellar walls and ceilings. It loves the sugars of the more spongiform oaks. It is a beloved essential for the makers of sourdough bread, and some brewers, but the enemy of others, and the dreaded enemy of those winemakers who think their wines should smell like fresh grapes.

To please these, and save them lots of money, Professor Isak “Sakkie” Pretorius and his wizard boffins at the Australian Wine Research Institute, at the Waite Campus in Adelaide, South Australia, have unwound the architecture of the DNA of Brett.

This is one of the most significant wine science discoveries of our age.

While winemakers had been able in the past to keep Brett under control by using sulphur dioxide, there was increasing belief that the yeast was adapting to this natural preservative, and is developing a tolerance to it.

Amusingly, Brett is a principal flavour of many of the wines of the north-west Mediterranean and the Iberian Peninsula: France, Portugal and Spain. A flavour much beloved of the English. Oh, and maybe Yorkshire. It’s in their beer. Oh, yes, maybe the Scots. It’s in their beer and their malt whisky – most people confuse it with peat. Ireland? Well of course. And the Belgians couldn’t live without it. The very same yeast the Australian winemakers need urgently to restrain is what gives the best beers in Belgium their distinction, thus the Brussells nomenclature, bruxellensis.

While the AWRI is obliged to make such science available to the biggest Australian wineries, most of these are not owned by Australians, so this new intelligence will quickly spread: even the Belge brewers will find this brilliant information to their advantage.

Most reasonable Australian winemakers seem capable of regarding a smidge of Brett as acceptable, if not quite unfortunate. Most seem incomprehensive of its nature; some like a little; some like a lot. Some even encourage measured amounts of Brett in their wines, especially those headed for Britain. Totally Brett-free wines, like the lo-oak hi-alc cordial fruitbombs that got Australia into the UK and the USA are increasingly derided by the same markets, which are returning to Bretty Old World favourites.

On behalf of his team, Pretorious (left) is highly excited about their genetic unwinding.

“As you know,” he said, “from the late 1990s through the early 2000s, the Australian wine industry has been very successful to combat this troublesome yeast. This was largely due to an AWRI campaign supported by winemakers to focus on pH and sulfite management as well as hygiene both in barrels and the winery environment. Their hard work led to a 90% drop in Brett spoilage … the Australian wine industry saved approximately $400 million over the past 10 to 15 years.”

With their usual lack of precision, winemakers regard Brett as something that smells of a range of things that stretch from barnyard, horse sweat, mouse piss, wet animal, rancid cheese and wet leather through Band-aid and burnt plastic to medicinal and metallic. That is a wide range of smells, in anybody’s language, and hardly scientific. But, for Bacchus’ sake, they’re not far off the smells of ancient cellars!

I find moderately-affected Bretty wines generally evoke powerful dreams and memories: briquettes and coal dust; the acrid, slightly woody smell of railway stations in the days of steam, combined with the hearty barnyard homeliness of the delivery Clydesdale there in its oiled harness.

Low Brett is more comforting saddle soap to me; too much is the acrid tickle of brown coal dust; briquettes is even worse. Briquettes do not smell like food.

While there is no doubt that a little Brett can add sensual earthy allure and complexity to some red wines, in high concentration it will literally gut a wine of its fruity character and flesh, leaving an unsatisfactory tannic husk. At different times, this level of infection has caused many great Australian winemakers, from Henschke to Cape Mentelle, considerable grief. Once Brett takes control, it costs lots of money to purge a heritage cellar of it, if indeed such a thing is possible.

Having spent one or two houses worth of money on replacing barrels and purging and sanitising cellars, many winemakers regret showing so much parsimony when they refused to shout themselves a proper barrel washer five years previous.

Unaware that the AWRI was about to announce such a significant achievement as it now has, I wrote about all this a month back on DRINKSTER (click) where I pointed out the high variance in people’s ability to detect Brett. This seems directly relative to the natural parallel incidence of the fatty isovaleric acid in the wine. IVA is a powerful pheromone which appears to influence the way different humans detect Brett: the threshold variance is enormous and seems to depend on one’s genetics.

Since then, I have enjoyed the rapid recourse Prof Sakkie has afforded.

In respopnse to the IVA line he typed “… from memory, about 20 years ago, Dr Thomas Henick-Kling (now at the University of Washington), expressed the view that iso-valeric acid is the compound responsible for Brettiness. Since then, the overwhelming body of research results pointed out that 4-ethylphenol is actually the culprit that makes wines smell Bretty. Our own data confirmed that. Although IVA (and a few other fatty acids) is also produced by Brettanomyces, we are confident that 4-ethylphenol (and to some extent, 4-ethylguiacol) is the ‘barnyard compound’.”

While this avoids acknowledgement that IVA seems to be the key to the way humans smell Brett, regardless of how Brett occurs or what it smells of, there is no doubt that the AWRI success will be of great use to anybody who deals with Brett, love it or hate it.

“It wasn’t an all-out ‘win’,” Pretorius explained. “Brett is still out there and current control strategies could accelerate the evolution of a ‘super’ strain that is resistant to sulfite treatment in the same way that super bugs have developed resistance to antibiotics. To future-proof our campaign against Brett, we need to develop tools to Brettanomyces strains that are increasingly becoming SO2 tolerant.

“The bottom line is that, as an industry we don’t want to use higher sulfite dosages to combat these sulfite tolerant strains,” he continued.

“We also know, if we spike (from zero to a lot) normal commercial wines with Brett’s signature compound, 4-EP, consumers start to dislike wines as soon as they can pick 4-EP up. So, from a consumer’s point of view it is a question of ‘Brett is bad’ and ‘we don’t want to have increased levels of chemical preservatives (SO2).’

“Our mission is therefore: ‘Boot bad Brett’s butt!’ ”

The process these clever scientists used is confounding. By mid 2009, they’d isolated 1.5 million ‘sequence reads” of raw data and had attempted to reassemble these, like a giant jigsaw, into the Brett genome. It became evident they needed more grunt in the computer department. Only after serious upgrades of their bioinformatics server did they manage to squeeze their 1.5 million ‘reads’ into 27,000 ‘contigs’, or contiguous DNA sequences.

This led to two full years of screengazing to seek matching pieces of DNA and re-assemble them.

“Late in 2010 there was a ‘lightbulb moment’,” Pretorius explained.

“There was a reason why the puzzle was so hard to put together: there were more pieces than there should be. The genome of the Dekkera strain under investigation did not have two copies of each DNA region - as is the case for many genomes, including humans. There appeared to be three. This triploid structure may be important in enabling Brett to survive in wine.”

Once this tricky puzzle was understood and the re-assembly completed, the researchers used bioinformatics tools to search the DNA sequence for genes likely to make Brett resistant to sulfite, by comparing them with databases containing all the genes known to science.

“We can now learn what makes this yeast resilient and identify chinks in its armour,” Pretorius explained. “A key gene involved in sulfite tolerance has been found, so that variability in tolerance between different strains of Brett can be better understood.

“Clearer diagnostic tests are now more likely, identifying whether outbreaks of Brett are more or less tolerant to sulfite treatment. When available, these tests will give winemakers the upper hand in knowing what ‘weaponry’ to use.”

Genetic scientists at the AWRI face a tricky impasse over their discoveries. The wine marketing authorities and councils strive to keep the clean, green image of natural wine, regardless of the industrial refinery nature of the business. The recent AWRI invention by GM of a mildew-resistant vine has been clobbered by the regulations: it’s not permitted outside the greenhouse, because the Australian wine business is GM-free.

I put this problem to Pretorius, asking whether the new Brett discovery will become a GM issue.

“Good question,” he said, pausing. “No, I don’t think so. Uncovering Brett’s genetic code is like taking a biopsy to learn what treatment would be available to us when Brett becomes more SO2 resistant. A new anti-Brett combat plan will not include developing GM Brettanomyces strains. Now that we know what genes are involved in the production of 4-EP, we will have to find ways to starve Brett from the precursors for 4-EP. For example, if one can take its ‘favourite food’ away, it won’t be able to convert these forerunner molecules into bretty 4-EP. Does this make sense?”

Uncommonly good sense, thankyou Professor. Congratulations, and well done. Respect.

DR TONI CORDENTE (L) WITH DR ANTHONY BOURNEMAN AT THE AWRI

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