The secret behind wine swirling

To reveal precisely how swirling, termed "orbital shaking" by experts, generates the distinctive wave that fluid dynamicists have long observed churning and aerating wine and other liquids as it propagates around the inner wall of the glass, the research team used advanced instrumentation to track and measure the liquid velocity of similar traveling waves they produced inside clear cylinders. The fluid dynamics of the familiar, intuitive wine swirling ritual has remained mysterious until now, EPFL senior scientist Mohamed Farhat explained about Ph.D. candidate and team member Martino Reclari's presentation of their findings to the APS division: "The formation of this wave has probably been known since the introduction of glass or any other kind of cylindrical bowl, but what has been lacking is a description of the physics related to the mixing and oxygenation." The researchers found the wave propagation displaced the liquid back and forth from center to wall and from bottom to top, generating a wave-induced pumping mechanism that enhanced mixing, especially near the surface close to the periphery; also, for each glass shape, a particular rotation speed and shaking diameter optimized mixing and oxygenation. Besides being of interest to wine enthusiasts, this study has relevance for reducing production costs and improving results in the field of biopharmaceuticals, according to Farhat. Cell cultures placed in large, cylindrical bioreactor tanks and swirled will mix and oxygenate better -- and will be more likely to thrive because of the gentler orbital shaking movements -- than those grown in conventional stirred containers, so long as the shape and shaking parameters of the cylindrical vats have been carefully matched, the researchers concluded.