High Friction Makes the Wine Dry?

dry wine tasting
Chemistry and physics are behind the wine taste. Credit: GANNA MARTYSHEVA/Shutterstock.com

Wine tasting has been elevated to an art form. The experts describe wine tasting as involving four sensory characteristics. The first sense (and most obvious) is taste. When tasting wine, you pay attention to the sweetness, acidity, bitterness, and saltiness. The second sense is touch, which includes the body (perceived weight), heat (related to the amount of alcohol), astringency (drying sensation in the mouth), texture, and persistence. Persistence deals with length (how long the sensations last in the mouth) and the finish (the sensation immediately after swallowing the wine). The next sense is smell. The aromas of wine are all the result of the grape variety, pressing, fermentation, and maturation. Finally, the sense of sight. Sight deals with the more complex ideas of complexity and structure but it also is as simple as the color of wine.

Some enologists (wine scientists) are particularly interested in the quality of dryness in wine. While people are good at judging the level of dryness with their senses, there is, to date, no objective measure of dryness.

People perceive wines as being dry for several different reasons. Wines that are not sweet or have low levels of sugar are considered dry. Wines with high alcohol levels (typically greater than 13%) are often called dry due to the burning or hot sensation in the mouth that masks other sensations such as sweetness. Finally, many red wines are considered dry because of the polyphenols they contain.

Polyphenols are micronutrients found in some plant-based foods that are full of antioxidants and various health benefits. Some of the best-known sources of polyphenols are dark chocolate, tea, berries and red wine.

Mature grapes taste astringent (dry) due to the number of tannins they contain. Tannins are naturally occurring polyphenols found in plants, seeds, and fruit skins. Grape tannin comes from the seeds, skins, and stems of the wine grape. Consequently, red wines typically have higher tannin levels than white wines due the extended length of time of contact between the grape skins and the juice, which allows the tannins to dissolve into the wine.

The higher the concentration levels of tannin in a wine, the more astringent or dry it will be. The tannin molecules interact with proteins found in the saliva and the reaction between the two results in fewer salivary proteins. Fewer salivary proteins mean less saliva to lubricate the mouth, and therefore the wine tastes dry.

However, as the saliva of each individual is unique to that individual, everyone’s perception of the dryness of a wine is not the same. As dryness is a perceived sensation, it can only be measured by human tasters.

However, an objective test to measure the dryness of wine would be beneficial for all winemakers. With an objective test, wines from different years and areas of the world could easily be compared. Current wines could be compared with rare wines that are not available for testing purposes.

One research group attempts to determine an objective method for measuring wine astringency. The group used both analytical methods (determining the different tannin sizes, their concentrations and how the tannins interacted with salivary proteins) and physical methods (using a machine to simulate friction forces between the tongue and palate when the tannins and saliva and interact as the greater the friction forces the dryer the wine). However, the results were contrary to the perceptions of the wine tasters, indicating that wines with fewer tannins resulted in greater friction forces indicating a dry wine. The researchers plan to investigate this contradiction further to help improve their understanding of wine dryness.

The article is based on the material of The Conversation.

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