Do you like Pastis? I must admit it took me a while to appreciate it.

Pastis is a French liquor made with anise and liquorice, and often other herbs. Pastis became popular after the banning of Absinthe, the famous spirit made with wormwood. Despite what most people think, Absinthe was unfairly convicted: the so-called Absinthe syndrome was actiually resembling more an alcoholic status (if you want to learn more on the story, please see here). Indeed, Absinthe is now back on the counter and quite available in Europe and North America (here, in Canada, you can find it at LCBO, next to Pastis). But as a matter of fact, when Absinthe became illegal, a lot of distilleries started to produce Pastis, instead. 

Pastis can be served  tout court as a digestive, although in France it is common to prepare a long drink by diluting the liquor 1:6 with cold water. Although I love both liquorice and anise, I confess I found that cocktail a bit sickening the very first time (don't hold me against me, please! :)). I had to try it a few more times until it became an acquired taste. 

What actually intrigued me, was the turbidity of cocktail Pastis. As a liquor, Pastis is a yellow-trasparent liquid, but once diluted with water, it turns milky.  Why?

Do you remember colloids? Well, that is the type of system that you obtain by diluting Pastis with water. Cocktail Pastis, as milk, is not a solution (that is always transparent), but rather a system where aggregates of molecules are dispersed in a liquid.

What happens when we dilute Pastis with water?

Liquor Pastis contains aromatic compounds as anethole, which is responsible of anise's aroma. 

Anethole is soluble in oil and alcohol, but not in water. When liquor Pastis is diluted, the essential oil of anethole become surrounded by water molecules. As anethole is insoluble in water, the essential oils associate in micro drops to minimize the contact with water. The dimension of those aggregates is such to provoke the scattering of light in all direction, which is responsable of opacity of the cocktail.

You can observe the same effect with other liquor as Sambuca, Absinthe, Ouzo...

What's about a Pastis, now? :)

Fonti

L. D'Ulivo, The absinthe challenge, Anal. Bioanal. Chem., 2014, 406, 1815-1816

L. D'Ulivo, Solution to the absinthe challenge, Anal. Bioanal. Chem., 2014, 406, 4011