Whether it’s Greek ouzo, French pastis or Turkish raki, when these spirits are diluted with water, the mixture becomes cloudy. The reason for this is that the aniseed oils contained in the spirit dissolve well in alcohol but not in water. The clear ouzo from the bottle has a high alcohol content at which the oil is fully soluble.

However, when water is added, the aniseed oils can no longer dissolve completely in the significantly reduced alcohol content. As a result, small droplets disperse finely in the drink, creating a milky appearance. Researchers at TU Darmstadt have now used this so-called ouzo effect to create oil droplets for a laboratory experiment. This led to a new discovery: such a droplet can resist a fluid flow and remain in place or even move upstream.