The "Ouzo effect":: Following the spontaneous emulsification of trans-anethole in water by NMR

Some aperitifs, like Pastis or Ouzo, are ethanol extracts of anis seeds. When diluted with water, these aperitifs, which are principally composed of water, ethanol and trans-anethole, become cloudy instantaneously. This phenomenon is the result of a spontaneous emulsification sometimes termed "Ouzo effect". By employing deuterated ethanol and water, it is possible to follow the aggregation process by NMR, using DOSY and TOCSY experiments. Analysis of these results permits us to propose an aggregation process mechanism by which trans-anethole initially forms small aggregates that are visible by NMR, which then coalesce to form small droplets of micron-size that are "NMR invisible".