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What makes wine dry? It's easy to taste, but much harder to measure

Time:2019-12-10 07:49wine - Red wine life health Click:

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When you take a sip of wine at a family meal or celebration, what do you notice?

First, you probably note the visual characteristics: the color is generally red, rosé or white. Next, you smell the aromatic compounds wafting up from your glass.

And then there’s the sensation in your mouth when you taste it. White wine and rosé are usually described as refreshing, because they have brisk acidity and little to moderate sweetness. Those low levels of sugar may lead you to perceive these wines as “dry.”

People also describe wines as dry when alcohol levels are high, usually over about 13%, mostly because the ethanol leads to hot or burning sensations that cover up other sensations, especially sweetness. People also perceive red wines as dry or astringent because they contain a class of molecules called polyphenols.

As an enologist – a wine scientist – I’m interested in how all the chemistry in a glass of wine adds up to this perception of dryness. People are good at evaluating a wine’s dryness with their senses. Can we eventually come up with a way to automatically assess this dryness or astringency without relying on human tasters?

What makes wine dry? It's easy to taste, but much harder to measure

Molecules in grapes give them their various properties. barmalini/Shutterstock.com The chemistry at the vineyard

Everything starts with the grapes. If you taste a mature grape skin or seed at harvest, it will seem dry or astringent to you, thanks to a number of chemical compounds it contains.

Large molecules called condensed tannins are mostly responsible for the astringency perception. These compounds are made up of varying types and numbers of smaller chemical units called flavanols. Tannins are in the same family of molecules, the polyphenols, that give grapes their red or black color. They tend to be larger in grape skins than in grape seeds, and consequently the skins tend to be more astringent, while the seeds are more bitter.

Grape varieties differ in how much of each of these compounds they contain. In Vitis vinifera cultivars, like Pinot noir and Cabernet sauvignon, the tannin concentration varies from a relatively high 1 to 1.5 mg/berry. In cold-hardy hybrid grapes found in the Midwestern United States, like Frontenac and Marquette, the concentrations are much lower, ranging from 0.3 to 0.7 mg/berry.

Factors in the vineyard – including site, soil qualities and amount of sun – affect the final concentration of tannins in the fruit.

What makes wine dry? It's easy to taste, but much harder to measure

Extracting tannins from red wines in the lab to characterize their chemical structure. Aude Watrelot, CC BY-ND The chemistry in your mouth

Basically, the more tannin there is in a wine, the more astringent it will be.

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