Characterizing emulsion formation in Absinthe as a function of temperature

Oil flavored alcohols are traditionally served by mixing them with cold water to form a louche: a microemulsion that turns the drink turbid, sometimes also referred to as the “ouzo effect”. Formation of the louche depends on the relative concentrations of water, ethyl alcohol and oil. Although the ouzo effect has been studied in ouzo and limoncello, it has not been characterized in absinthe. Previous work demonstrated distinct differences between ouzo and limoncello. Also, little has been done to examine the role of temperature in the louche. Our work examines the emergence of the louche phase in absinthe by measuring the optical transmittance of the solution as a function of ethanol concentration at multiple temperatures. Optical transmission was measured through a temperature-controlled sample of absinthe and the change in transmission, accompanied by formation of the louche, was recorded as water was added to the sample, revealing an inverse relationship between temperature and critical ethanol concentration at which louche forms. The transition from clear solution to louche is an s-shaped curve and by fitting this with a sigmoid function we have determined that louche formation is a first-order phase transition.