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harvey steiman at large

News from the Laboratory

Science marches on, one sip of wine at a time
Photo by: David Yellen

Posted: Aug 21, 2013 4:22pm ET

I love science. I grew up reading Isaac Asimov essays, and I lap up the latest scientific papers about wine. I came across a few nuggets in recent weeks; they both got me thinking. Maybe they will for you too.

Buried in a report on how to detect brettanomyces in wine was one revelation that helps explain why some bottles taste great when you buy them but can reek of brett after a few years of cellaring. Though physically harmless, brett yeasts can multiply and an individual wine can end up picking up (depending on concentration and the type of the responsible cells) leather, spoiled meat, barnyard, Band-Aid, garbage or fecal aromas. Some people love it. I don't.

I have more than a few bottles of big-name Bordeaux from the 1980s and 1990s that were delicious when released, but opening them now is a roll of the dice. Some are fine, many reek. Now at least I have an explanation for how this can happen.

Winemakers routinely add sulphur dioxide to wines to ward off bacterial contaminations, including brett. The organisms can't grow while there's plenty of SO2 in the wine, but as the SO2 dissipates, they can proliferate. Responsible winemakers routinely test for the presence of brett before bottling, and can respond to its presence by filtering or other treatments. But the little beasts could still be lurking, undetected, waiting to awaken from their slumber.

A new method for brett detection developed by scientists in Italy, detailed in a study published in the Journal of Food Science, uses quantitative polymerase chain reactions to detect brettanomyces DNA. The new process, using the same technology that doctors use to quickly confirm the presence of an infectious disease, can reveal the presence of brett even while lying dormant under a blanket of sulphur dioxide. I lift a glass of (brett-free) wine to those who developed this testing method and to those who can use it to bring me yummier wine.

Micro-oxygenation is a winemaking technique in which trickles of oxygen are released into fermenting wine. It's long been known that this stabilizes color, softens texture and, in general, makes a wine more drinkable sooner. A study from Australia, published in the Journal of the Science of Food and Agriculture, tested preferences for Mornington Peninsula Cabernet Sauvignon made with two levels of micro-ox (25ml of oxygen per liter and 50ml oxygen per liter) and a control sample with no micro-ox.

Lab tests showed that the micro-ox samples had deeper color and less tannins to roughen up the texture. Although the control wine was deemed fruitier by a panel of 30 enology students, four professional winemakers and one critic, they found the micro-ox samples to be more complex and round. Most interesting, to me, was that almost half of the expert tasters liked the control sample best, while 71 percent of consumers (a group of 51 winery visitors and non-expert staff members) preferred some level of micro-ox, with 40 percent preferring the mid-range 25ml sample.

These results fall in line with the notion that consumers love softer, rounder, more approachable textures. So do I, usually.

Don Rauba
Schaumburg, IL —  August 22, 2013 1:14am ET
Very intriguing, on both counts. Thanks for sharing this Harvey.
Scott Politte
Des Moines IA —  August 22, 2013 11:38am ET
I recently ordered an 88 Ducru at a wonderful restaurant I have been going to for 20 years. It was extremely ripe with brett, and when they brought out a second bottle, it was equally tainted. We settled on an 06 Montrose. I was eagerly anticipating a wonderfully aged Bordeaux. How disappointing. I am glad it can be tested for now.
Troy Peterson
Burbank, CA —  August 26, 2013 3:05pm ET
Will they ever be able to perform such a test without breaching the bottle? I know some tests can be done externally to determine if a wine has already turned to acetic acid. Just curious.
Adam Lee
Sonoma County, CA —  August 27, 2013 10:27am ET
Harvey,

There was a fascinating study entitled, "Who Invented Brett" by Adrian Coulter of the Australian Wine Research Institute that was published in Practical Winery and Vineyard in January of 2012 with regard to brett and its variability from bottle to bottle. Some of the key points were:

1) A wine that was stored in Austraila showed 812 ug/l (don't have the right symbol) of brett compared to 1470 for the same wine (different bottle...but a small lot, so bottled at the same time) for a botle shiped to the EU and returned.

2) Variation from bottle to bottle of brett....from 34ug to 1401ug (other variations from 117 to 2550, 675 to 1204, and 812 to 1470). Each set of numbers are from different bottles of the same wine.

3) The differences in brett were seen and largely blamed on oxygen ingress from cork (especially if stored upright), while bottles under twistoffs didn't show the same amount of brett variability.

Yet another reason to favor twist off closures.

Adam Lee
Siduri Wines

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