Wine is so delicate that a drop of water makes you faint.
Oscar Wilde (1854-1900) is one of the most universal late 19th century English writers due to his fine irony and wit. At the peak of popularity after his only novel, "The Picture of Dorian Gray", and the masterful play "The Importance of Being Earnest," he was accused (and imprisoned) of homosexuality, something inexcusable in English Victorian society. He died in poverty in Paris.
The “tears of wine” (or “legs” for the English, “windows” for the Germans) is a characteristic often used to value a wine and equally often with totally wrong arguments. In fact, the presence of “tears” provides very little information about the composition of the wine and nothing about its quality. They are associated with greater unctuousness in the mouth of the wine (greater body) and are due to a physical effect associated to a mixture of alcohol and water, not, as it is often mistakenly associated, with the glycerol content or the quality of the wine.
The first correct explanation for this phenomenon was pointed out at the end of the 19th century by James Thomson (an English physicist), developed a few years later by the Italian physicist Carlo Marangoni and theoretically explained by Willard Gibbs somewhat later, which is why it is called the Gibbs-Marangoni effect.
In short, a mass transfer occurs at the interface of two fluids (water and alcohol) that separate as a result of their different surface tension. In this way, wine, which has a lower surface tension than water, forms a thin layer on the surface of the glass. At the end of the meniscus, alcohol would evaporate much faster than water, generating, on one hand, the formation of a drop of water (the tear) that would slide down due to the effect of gravity and, on the other, a suction effect on the wine causing it to move up in the glass.
The phenomenon then depends exclusively on the amount of alcohol present (more alcohol means a greater intensity of the effect and, therefore, more tears), on factors that may affect surface tension (such as the presence of surfactants) or that affect the evaporation rate of alcohol (such as temperature or humidity). The presence of higher sugar content, including glycerol, only causes the viscosity of the wine to increase, causing the tears to flow more slowly.
As a side note, it is believed that it was Marangoni who sparked Albert Einstein’s fascination with physics when he shared a vacation with him as a 16-year-old in the summer of 1895 (1). So, who knows? Perhaps we owe the birth of modern physics to an interesting evening around a glass of wine…
(1) Christian Bracco. Albert Einstein and the Marangoni family. Società Italiana degli Storici della Fisica e dell’Astronomia, Sep 2017, Bari, Italy. hal-01742996.