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May 30, 2022 View:

French researchers reveal source of wine bitterness

A study has revealed that a compound in oak barrels may be responsible for some of the less desirable flavors in wine.

Image from: Wine Click

Lovers of full-bodied reds and Chardonnay wines know they have the oak barrels to thank for the toasty, nutty vanilla flavors and the silky texture they love in their wines. But does the wood add bitterness to the spirits? It makes sense: oak contains tannins, and tannins have an astringent effect.

In a recently published study, researchers from the University of Bordeaux focused their attention on a phenolic compound they believe is the main culprit in barrel bitterness: coumarin.

Many plants, including oaks, contain coumarins, compounds that are corrosive and deter predators, explains Dr. Delphine Winstel, who formed the basis for the study, published last month in the Journal of Agricultural and Food Chemistry, entitled "The Role of Oak Coumarins in Wine and Spirits Flavor: Identification, Quantification, and Sensory Contribution through Perceptual Interactions.

But Dr. Winstel and her colleagues wanted to find out which coumarins were getting into the barrels. They took some samples from Seguin-Moreau and succeeded in identifying five coumarins known to be present in oak and one previously undiscovered coumarin, says Dr. Winstel: It is always very satisfying to find a compound that has never been identified in wine. It is called fraxetin and has a very bitter taste.

How much of the work can coumarin actually be contained in the glass and at what level can it be detected?

To find out, the research team held a blind tasting of a spicier than usual sample of coumarin-containing wine and alcohol for 22 trained tasters. To block out the noxious smell of coumarin, the research team covered their noses and dutifully tasted the coumarin. I'm not sure tasting bitterness in a watery alcohol solution in the morning is the greatest pleasure in life, says Dr. Winstel, but every team member was diligent!

Dr. Winstel also analyzed the coumarin content of 90 commercial wines, as well as some spirits: red wines from Bordeaux and Burgundy, white wines from the Loire and Alsace, cognacs from the 1970s, and so on. They found that red wines had higher coumarin levels than white wines, but otherwise no specific region or appellation had higher coumarin levels than white wines.

While the team has determined whether coumarin levels are too high and is closer to knowing how coumarin levels vary from tree to tree and even from barrel to barrel, there is still much work to be done These new findings could still have a real impact on the wine industry. Winemakers may one day be involved in limiting the amount of coumarin in their wines.

And any discovery will make the world of wine science a little sweeter.