GAVIN SACKS: One of the things that makes wine remarkable as a consumer product is the sheer variety. Which means if you went to every wine store in the United States, looked at all the different vintages, you could probably find a half million, maybe even close to a million different wines available for sale.
There is remarkable tolerance, not just tolerance, but appreciation for variation in wine that you don't get with other products. And these wines are made using different grape varieties. So grape variety, for example, Merlot is a grape variety. Chardonnay is a grape variety.
Almost all of these grape varieties that we use come from a single species of grape native to Western Asia. And these grapes are very well adapted to a Mediterranean climate, but not to the East Coast of the United States.
And if you're going to try to grow these European wine grapes on the East Coast, or almost any region that has cold winter temperatures and disease pressure, you expect to have to do a lot of work in the vineyard to make that possible.
But there are wild grapes native to this area. These are the grapes that you would see climbing up the sides of telephone poles, or sprawled out next to a river bank. These grapes evolved in our local climate, around our local pests. They have figured out a way to survive. They have sufficient disease resistance that they don't need to be sprayed. They have sufficient cold hardiness that they survive each year.
What if we could take advantage of those properties and make wine from those grapes, and not need to put all these inputs in when making wine? There's a problem, though. Consumers have a pretty wide tolerance for what they like in a wine, but they usually can agree pretty well about what they don't like in a wine. And these wild grapes are often very poorly suited to consumers' preferences for flavor.
Many of these wild grapes have excessive amounts of acidity, and it's that acidity that leads to a perception of sourness. So a Cabernet Sauvignon or a Chardonnay that you get in a wine store, typically it's going to be about 0.5% acid by weight.
The amount of acid that you expect to find in one of these wild grapes can be five six times that amount, maybe 2% or 3% acid by weight. That's closer to the amount you expect to find in a cranberry or in some lemons.
Many of these grapes produce wines that have excessive herbaceous or vegetal green type aromas. That's fine if you're having a salad. It's not so fine if it's at really high concentrations in your wine.
Many of these wild grapes, they will produce wines with very low concentrations of tannins. And tannins are one of the most critical compounds for the mouthfeel of red wines.
So tannins are compounds with the ability to react with proteins. When you take a sip of a red wine, or a sip of green tea, or some raw cacao or unsweetened chocolate, take a little bite or a sip, and what you notice is it feels like your tongue doesn't move very easily over your lips or over the roof of your mouth. It feels a little sticky and grippy.
And while that might sound a little unappetising, the way I described it, having a little bit of this grippiness is critical for the quality of red wine. Wines that have too little tannin are described as being thin or having poor body.
So these are the some of the challenges, then, that a grape breeder has. If they want to take advantage of these wild grape varieties, how do you extract out only the genetic parts of these wild species that provide good growing properties, but leave behind the parts that give you undesirable flavor?
And that's where I as a chemist come in. So how do we help the grape breeders? The grape breeders develop populations. That is, they'll take two grapes-- maybe one's a European wine grape, and the other's a wild grape with very different properties.
Let's consider the case of methoxypyrazine, those vegetal, green pepper aroma compounds. The wild grape often will have very high concentrations of these compounds, and the European wine grape might have very low concentrations. If they get crossed and they have lots of offspring, those grapes that come from the parents are going to have a range of methoxypyrazines in the fruit.
So how do we measure these? The device that we use is called a GCMS, which stands for gas chromatography mass spectrometer. And the way a GC is, for lack of a better term, it's an overpriced convection oven. You can use these to make an amazing mini pizza, if you so chose. Or you can use these to do a small scale distillation.
So you inject an extract from your wine with lots and lots and lots of volatiles in it. But they'll differ at the temperature where they boil. And as they come off of the gas chromatograph, they get directed to a mass spectrometer, an MS.
I think of an MS as sort of a molecular scale. It weighs molecules. And different molecules have different molecular weights. And we can measure how much methoxypyrazine is in each one of those offspring, and then compare it to the genomes of those offspring, and figure out what genes are responsible for making high concentrations of the methoxypyrazines.
And then eventually, the breeders can use that information so that early on they can select against those crosses that have unacceptably high amounts of methoxypyrazine.
BRUCE REISCH: When I first started in this position 35 years ago, we would plant everything out to the field and evaluate every seedling and eliminate the worst and save the best, hoping to combine the best features of each parent. But there was no genetic selection involved.
So if Gavin and his team can tell me some of the molecular markers that influence methoxypyrazine levels, I can do a DNA test shortly after I germinate seedlings, and eliminate the ones with high methoxypyrazine within two months of germination.
Normally, it would take us three to five years before we saw fruit, and before we could even test for methoxypyrazines. But if we get fruit traits that we can select based on the DNA test early on in the process, we gain a great deal of efficiency in the work that we're doing.
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Gavin Sacks, associate professor of food science, explains how his research on wine flavor is contributing to the work of the USDA-funded VitisGen project. To learn more visit
www.VitisGen.org. Support provided by USDA National Institute of Food and Agriculture Specialty Crop Research Initiative Award No. 2011-51181-30635.