PARIS - It’s a simple gesture, something lovers of good wine do automatically. They swirl the wine in their glass to aerate it and release its aromas. But few do so in conscious awareness that behind this slow rotation lies a complex problem of fluid mechanics that has kept researchers at the Lausanne branch of the Swiss Federal Institute of Technology (EPFL) busy for three years.
“We realized that swirling wine in a glass was a very clever mechanism that mixed the liquid gently but also didn’t use much energy,” says Mohammed Farhat, a researcher at the EPFL who heads the Swiss team. “However, it was virtually impossible to create a mathematical model of the phenomenon, which involves very complex aspects of fluid dynamics.”
A specialist in cavitation, Farhat was looking for an effective, non-destructive way to mix biological cell cultures – a great challenge in the pharmaceutical industry -- and noticed that the light flick-of-the-wrist gesture that’s so habitual for wine tasters presented all the requisite qualities needed to do so. It could also be reproduced on a large scale in huge bioreactors containing several thousand liters of cells.
Farhat has three young doctoral candidates working on the technique known as “orbital agitation” and has also come up with a comprehensive experimental device to measure all the parameters of a fluid rotated in a glass. “We saw that turning the glass creates a wave that makes the wine move from top to bottom but also from the center towards the exterior. There are no ‘dead areas’ where no mixing is taking place,” Farhat said.
By varying parameters like the speed of rotation, height of the liquid, or diameter of the receptacle, infinite wave forms can be obtained, some more, some less effective to mix or oxygenate liquid, or to make it evaporate. The work was presented for the first time at this month’s 64th meeting of the American Physical Society’s Division of Fluid Dynamics in Baltimore, Maryland.
“In the case of wine, the main thing you look for is not mixing but oxygenation, which makes it possible to oxidize certain compounds that produce aromas, and to a lesser extent evaporation, to remove some of the alcohol in the glass,” Farhat explains.
“Finding the perfect gesture”
Farhat’s team works with a school in Nyon, near Geneva, that trains enologists and sommeliers to help them “find the perfect gesture.” Formerly, the rotation of glasses was always conducted empirically, with no scientific method behind it. The new science has left wine lovers with endless material for discussion as regards to size and form of glasses, as well as the ideal strength and duration of movements to use with various grands crus.
Farhat and his young doctoral candidates have successfully determined three parameters that make it possible to describe how this phenomenon operates, whether it be in a glass of wine or an industrial vat containing several thousand liters of cells.
“We will be working with a pharmaceutical company so we can determine the best possible configuration for mixing cell cultures on a large scale,” says the scientist. “The most important thing is to get to the point where the cells grow rapidly and to mix them effectively without destroying them.”
Read the original article in French
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