  Ouzo is a well-known drink in Mediterranean countries, with ingredients
water, alcohol and trans-anethole oil. The oil is insoluble in water, but
completely soluble in alcohol, so when water is added to the spirit, the
available alcohol is depleted and the mixture exhibits spontaneous
emulsification. This process is commonly known as the louche or Ouzo effect.
Although the phase boundaries of this archetypal ternary mixture are well
known, the properties of coexisting phases have not previously been studied.
Here, we present a detailed experimental investigation into the phase
behaviour, including tie-lines connecting coexisting phases, determination of
the critical point (also called the plait point in ternary systems) and
measurements of the surface tension and density for varying alcohol
concentrations. Additionally, we present a theory for the thermodynamics and
phase diagram of the system. With suitable selection of the interaction
parameters, the theory captures nearly all features of the experimental work.
This simple model can be used to determine both bulk and non-uniform (e.g.
interfacial) properties, paving the way for a wide range of future applications
of the model to ternary mixtures in general. We show how our accurate
equilibrium phase diagram can be used to provide improved understanding of
non-equilibrium phenomena.
