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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.
Sensation - Mouth - White - Wine - Rosé
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.
Enologist - Wine - Scientist—I - Chemistry - Glass
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?
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.
Molecules - Tannins - Astringency - Perception - Compounds
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...
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