Tears of wine (Marangoni effect)
Why do clear droplets or 'legs' of liquid form and slide down the inside of a wine glass above the surface of the wine?
History and references
Settled in 1992 by Jean-Bernard Fournier, Anne-Marie Cazabat (College de France).
James Thomson gave the first physical explanation of wine's 'tears' in 1855, correctly attributing them to surface-tension gradients from differential evaporation of alcohol and water (the Marangoni effect, though named after Carlo Marangoni's independent 1865 work). The phenomenon lacked a full quantitative theory until Jean-Bernard Fournier and Anne-Marie Cazabat's 1992 study derived a self-similar diffusive-wetting law for the climbing film and related instabilities (fingering, a 'star' pattern) at its edges. Later work (e.g. a 2015 Scientific Reports study and a 2019 theory of 'undercompressive shocks') has continued to refine the quantitative picture of the film dynamics, but the core Marangoni mechanism identified by Thomson has stood since the 19th century.
A glass of wine displays, in miniature, the same surface-tension-gradient physics that drives currents across the open ocean.
Explanations that circulated
- That the tears are simply caused by evaporation cooling the wine's surface (a thermal-Marangoni idea); the dominant effect is instead a solutal Marangoni flow driven by the faster evaporation of ethanol (lower surface tension) relative to water near the thin climbing film, which pulls liquid upward along the glass wall until gravity collects it into falling droplets.
References
- Tears of wine, J. B. Fournier, A. M. Cazabat, EPL (Europhysics Letters), 1992
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