Characterizing the effects of Temperature and Ethanol Concentration on the louche of Absinthe.

Oil flavored alcohols are traditionally served by mixing them with cold water to form a louche: a microemulsion that turns the drink opaque because of the interactions of the alcohol with water, which it dissolves, and the oil, which is disperses. When there is sufficient water the oil phase precipitates, forming the louche. Thus, characterization of the louche depends on the concentrations of water, alcohol and oil. Absinthe has not been as well characterized as other oil flavored alcohols such as Limoncello or Ouzo with no studies on either a ternary phase diagram or on the louche phase. This work examines the emergence of the louche phase in absinthe by measuring the optical transmittance of the solution as a function of both: (1) the concentration of ethanol and (2) the temperature, which can be separately varied. The laser transmission was measured through a temperature-controlled sample of absinthe. The change in transmission was recorded as water was added to the sample, revealing an inverse relationship between temperature and ethanol concentration at which louche forms. There are also two different steps in the louche suggesting two different micro-emulsions form depending on the concentrations.