ANNA KATHARINE MANSFIELD: When we think about wine quality, the components that really are most important are those that give us aroma and flavor, so everything that we smell or that we taste when we swirl the wine and sniff it, or put the wine in our mouths. But humans are inherently visual creatures. We tend to experience the world through our eyes more than with our noses.
We don't usually walk around smelling things, unless there's something that smells really good or really bad. So when we interact with the wine, even though the components that give it color aren't very important, as far as aroma and flavor are concerned, our perception and our pleasure of the wine is impacted quite a bit by the color that we see, especially in red wine.
The color in red wine is predicated by different anthocyanin. They're the same color compounds that you find in other plants like flowers. Even the things that turn delphinium blue are also in other fruits and vegetables. Like the tannins that we find in wine, anthocyanins are found primarily in the skin and the layer of tough cells right under the skin of a grape.
So in order to get a really nice, deep color in our red wines, we've got to extract all of those tannins and those anthocyanins from a really-- it's a pretty small and pretty tough layer. So when we look at the individuals that make up the populations in the VitisGen experiment, what we are looking at are actually those anthocyanins.
So what we're finding in Vitis vinifera-- most of the anthocyanins are monoglucosides, which means that they are pretty readily available to bind with components that help make them stable. However, in hybrids we're seeing many more of the diglucosides, which aren't as amenable to binding and stabilizing themselves.
So the colors that we see in hybrid wines can be from bright pink to very, very dark with a black or deep blue or even a deep purple undertone. And that generally just looks a little weird to people who are used to drinking Cabernet Sauvignon and Merlot.
There's a visual disconnect. Whether they're aware of it or not, it can impair their impression of the quality of the wine, because it just doesn't look quite right. So the way that we look at these anthocyanins is actually through a method called HPLC, or High Performance Liquid Chromatography. So what we're then able to do is quantify the amount of each of the anthocyanins that we find by sort of breaking them into individual pieces.
What we're finding then is that in any population that we get, there's a variation in the amount of these monoglucosides that we want to have vinifera-like color. And we can look at the concentration in each one and make pretty much a graph, where we go from the ones with the highest amount of this vinifera-like pigment, all the way to the ones that have the lowest amount.
So that can help us select the color, especially if some of those individuals also are showing favorable traits for-- say, level of acidity, aroma, and flavor, and things like that. So it's just another way to help us make a decision about how vinifera-like or how amenable for traditional wine production these hybrids are.
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Anna Katharine Mansfield, associate professor of enology at Cornell's NYSAES in Geneva, NY, discusses her work to identify the traits that give wine its color, part of the USDA-funded VitisGen project. To learn more visit
www.VitisGen.org. Support provided by USDA National Institute of Food and Agriculture Speciality Crop Research Initiative Award No. 2011-51181-30635.