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WSU’s Voice of the Vine- What’s That Smell, Leafroll, Wine Center

Posted by | January 30, 2014

What’s that smell?

It’s a Monday morning inside the WSU sensory science lab where volunteers meticulously and anonymously sample everything from baked trout to french fries to wine, helping scientists glean information about the human senses.

With the push of a blue button, a stainless steel panel lifts and a pair of hands slide forward a cup of water and three glasses of today’s fare: merlot.

During a red wine aroma study, panelists were asked, "Which one of these is not like the others?"
During a red wine aroma study, panelists were asked, “Which one of these is not like the others?”

But, like the dozens of other panelists in the lab today, I won’t taste the wines—we’ve all come to sniff.

We start with the glass on the left and work to the right, pinpointing which one is not like the others, and sniffing water between sets to clear our senses. At first, it’s difficult to identify which one is different (perhaps, it’s my novice nose), but as the third of four sets of wine is presented, a potent, “chemical” aroma dramatically reveals the odd glass out.

The culprit? The researchers have added a chemical solution to the wine that causes a musty, plastic, barnyard smell. It’s called 4-ethonyl catechol (4EC). It comes from a yeast called Brettanomyces that affects red wines and sometimes builds up in wine barrels. It releases an unpleasant aroma that winemakers want to avoid in their final product.

Dr. Carolyn Ross’ team designed this particular test panel to find out what concentration of the aroma is noticeable to people.

While it’s a tiny concentration, it can make the difference between whether or not someone decides to take that first sip. With more than 10 million receptors in the olfactory system that controls our ability to smell, aroma is a big influencer on taste.

Ross said about half of the panelist sniffers could identify the compound when it was present in a very small amount: 823 parts per billion. To put that in perspective, Ross explains that one part per trillion can be compared to one drop of water diluted into 20 Olympic-size swimming pools.

Alison Baker, a food science/viticulture and enology graduate student, passes wine samples to a volunteer panelist in the WSU Sensory Evaluation Lab.
Alison Baker, a food science/viticulture and enology graduate student, passes wine samples to a volunteer panelist in the WSU Sensory Evaluation Lab.

They then decided to take the wine samples one step further and see what the new electronic tongue would reveal. Ross found it interesting that the e-tongue could distinguish components of aroma at all, and that its senses were even a little more sensitive than the average panelist when it came to identifying the 4EC.

“It’s a compound we associate with aroma, but the e-tongue is telling us that it can distinguish different components (of sweetness, sourness, bitterness and other attributes),” she said.

Of course, there are some aspects of aroma the e-tongue can’t identify and must be left to the unique experience of human beings. In the right amounts, some people say 4EC gives the wine complexity. But personal associations with the smell can also influence whether someone finds the smell tolerable or even pleasant.

There are differences in people’s sensitivity when it comes to smells and scientists have even explored how genetic differences impact the way a person perceives an aroma.

“Our sense of smell is also tightly tied to our memory and our sense of emotion,” Ross said.

So, while many of us left the sensory test lab with the experience of a new smell (and a participatory gift certificate to the university creamery and Ferdinand’s), it’s one that consumers will hopefully not have to sense in their wines any time soon, thanks to the work of sensory scientists and citizen scientists discovering more about what our noses know.

If you’d like to participate in sensory panels, you can “Give Your Input” at http://sfs.wsu.edu/sensory/. Ross, her fellow colleagues, and WSU graduate students will be presenting their work from sensory lab panels at the Washington Association of Wine Grape Growers Feb. 5-7 in Kennewick, Wash. http://www.wawgg.org/index.php?page_id=38.

-Rachel Webber

‘Blended Learning’ a success in early reviews

 

WineBottlesGreat Northwest Wine, an online platform covering wine reviews and news, stamped WSU’s student-made wine, a dry riesling, with an “Excellent” this month. The riesling is the first in a series of student-made wines planned from the WSU viticulture and enology program. The new tradition of blended learning is bringing together students, alumni, winemakers, growers and wine enthusiasts to uncork the possibilities.

“A product of Lonesome Spring Vineyard and Olsen Vineyard, its aromatic profile focuses on Key lime, Granny Smith apple and pineapple,” Great Northwest Wine writes. “Inside, it’s bright and nicely crispy with more lime and apple, backed by an undertone of orange with a salty texture.” Read more from the review, here.

The next wine from the ‘Blended Learning’ series, a red blend, was bottled in early January. Learn more about wine science at http://wine.wsu.edu/campaign/.

Grapevine leafroll: diagnosing the unseen

Grapevine leafroll is one of the most economically important virus diseases affecting productivity of vineyards around the world, and it’s kind of like a person affected with the flu, said WSU plant pathologist Naidu Rayapati.

A few years ago, while testing leaf samples from Washington vineyards for virus diseases, Rayapati unexpectedly found Sangiovese vines in one vineyard tested positive for grapevine leafroll-associated virus 2 (GLRaV-2) — but virus-positive vines weren’t showing any symptoms of leafroll disease.

A Sangiovese leaf showing leafroll disease symptoms. It tested positive for Grapevine leafroll-associated virus 3. Photos courtesy Naidu Rayapati.
A Sangiovese leaf showing leafroll disease symptoms. It tested positive for Grapevine leafroll-associated virus 3. Photos courtesy Naidu Rayapati.

Symptoms of leafroll disease in red grape cultivars typically include blotchy shades of purple and red colors on leaves and grapes of affected vines showing delayed and uneven ripening. When left unmanaged, the disease can easily spread throughout the vineyard, leading to serious problems for vineyard production. Rayapati said it usually results in 20 to 25 percent yield loss.

So how can you tell if a plant is sick, if it doesn’t appear sick?

The proof is in the plant

“Our findings of asymptomatic infections underscore the need for using specific diagnostic techniques for virus infections instead of just (looking),” Rayapati said. “By focusing on visual symptoms alone you may miss viruses causing asymptomatic infections.”

At the WSU Irrigated Research and Extension Center in Prosser, Rayapati and his colleagues recently sequenced the complete genome of one GLRaV-2 isolate from many different virus isolates in the grapevine leafroll virus family. The team published the details on the genetic make-up of this isolate that causes asymptomatic infections in cv. Sangiovese in Virology Journal. This article was designated as “highly accessed” by the journal, indicating broader interest and impact of this research publication.

A Sangiovese leaf showing no leafroll disease disease symptoms, but tested positive for Grapevine leafroll-associated virus 2. Such asymptomatic infections make it difficult to spot virus infections in a vineyard.
A Sangiovese leaf showing no leafroll disease disease symptoms, but tested positive for Grapevine leafroll-associated virus 2. Such asymptomatic infections make it difficult to spot virus infections in a vineyard.

“We can use this (genetic) information to (clarify and describe) the biological features of virus strains causing asymptomatic infections in wine grape cultivars. For example, we can study whether a virus strain can cause asymptomatic infections in different wine grape cultivars or determine if this phenotype is cultivar-dependent. Addressing these practical questions will advance our efforts in managing diseases in vineyards,” he said.

They can also use this genetic information as a basis to explore future incidences of leafroll virus strains causing asymptomatic infections in Washington vineyards.

Preventing grapevine leafroll

Naidu and his team’s work is part of an even larger effort to ensure virus-free, clean plants. Impact of viruses on plant health and wine quality is one of the priority areas of concern for the Washington wine industry as well, he said. While a plant with the asymptomatic virus may not appear sick at first, it is a matter of time–even a few seasons–before the plant starts to visually express the symptoms.

And, just as some people get a flu shot in the winter to manage that virus, growers can take preventative steps to stop grapevine leafroll viruses from spreading, too. The first line of defense is prevention, Rayapati said, which is why it’s important for cuttings to be tested for viruses before planting. Because grapevines are perennial crops, once they are planted they won’t be removed for thirty to forty years or even longer, and neither will any virus, if vines are infected at the time of planting.

“That’s why we encourage growers to think carefully and plant high quality planting material,” he said, “so they can have a good crop in the future.”

This article is based on the article “Molecular characterization and impacts of a strain of Grapevine leafroll-associated virus 2 causing asymptomatic infection in a wine grape cultivar” in Virology Journal (http://www.virologyj.com/content/10/1/324).

-Rachel Webber

Wine Science Center “Hard Hat” Tour on Feb. 4

Leaders in the development of the WSU Wine Science Center gathered at the groundbreaking last November.
Leaders in the development of the WSU Wine Science Center gathered at the groundbreaking last November.

Join WSU on an exclusive tour of the Wine Science Center construction site at the WSU Tri-Cities campus, Tuesday, Feb. 4 at 2:30 p.m.

Participants can meet in the Consolidated Information Center in the Art Center at 2770 Crimson Way, Richland, WA. Closed-toe shoes are required and hard hats will be provided. WSU representatives will escort visitors to the construction site and the tour will end around 3:30 p.m. You can RSVP here.

Keep up-to-date with construction on the Wine Science Center at WSU Facebook page: https://www.facebook.com/winesciencecenter.