Unlocking the secrets of ouzo’s cloudy transformation

Research could have implications on the emulsification and stability of new materials.

Physicists and mathematicians have turned their attention to a fascinating observation that has intrigued scientists and cocktail enthusiasts alike: the mysterious way ouzo, the anise-flavoured liquor, turns cloudy when water is added.

The research, which involved experts from the University of Edinburgh, Loughborough University and Nottingham Trent University, has resulted in a new mathematical model that offers insights into the spontaneous formation of microscopic droplets and how they can remain suspended in a liquid for a long time.

Revealing the maths taking place in the glass could have far-reaching implications, such as the creation of new materials, especially in fields such as pharmaceuticals, cosmetics, and food products, where the stability and distribution of microscopic particles are critical.

When water is added to ouzo, microscopic droplets form which are a result of the anise oil separating from the alcohol-water mixture. This causes the drink to turn cloudy as the droplets scatter light. The emulsification - the suspension of well-mixed oil droplets in the liquid - is something that requires a lot of energy in other systems and foods, but in the case of ouzo, it happens spontaneously. What’s also surprising is how long these droplets, and the resulting cloudiness, remain stable in the mixture without separating, especially when compared to other food emulsions.

By mixing alcohol, oil, and water in varying proportions, the researchers were able to observe phase separation and measure key properties like surface tension.

They used this data and a statistical mechanical modelling method known as ‘classical density functional theory’ to develop their mathematical model.

This model has been used to calculate a phase diagram that details the stable combinations of the ouzo ingredients.