louche is a French term meaning cloudy, disturbed (as in silty water), shadowy, and—by extension—disreputable. It is used to describe the clouding effect in absinthe upon adding water. It is also known as the “ouzo effect.”
Absinthe is rich in anethole, the essential oil derived from aniseed, star anise, and fennel seed that is responsible for absinthe’s licorice-like flavor. This oil dissolves readily in high-proof alcohol but is insoluble in water. During dilution, when the water-to-absinthe ratio reaches a certain point, the anethole drops out of solution and forms a suspension of microscopic oil droplets in the water—a micro-emulsion or colloid—creating the attractive, opalescent, cloudy effect known as the louche.
A proper louche is among the characteristics used to evaluate fine absinthe, not merely for its visual aesthetic but as a gauge of flavor balance and finesse in craftsmanship. The louche of a properly prepared glass of absinthe should be opalescent, translucent, and glowing. It is best observed in natural daylight. It should not be either too opaque or too transparent, indicating the absinthe contains either too much or not enough aniseed, respectively. A thick, milk-like, opaque louche will present an overpowering aniseed character, more like ouzo or sambuca, numbing the tongue and obscuring the finer nuances of the more delicate herbs. A thin louche will provide an insipid and watery drink with little character. Some faux absinthes, common to central and eastern Europe, avoid the aniseed flavor (which is why they are categorized as faux absinthe). These often contain gums and resins or other oil-rich spices to obtain the expected louche. This shortcut was a hallmark of an improperly made absinthe in the nineteenth century, just as it is today.
Nathan-Maister, David. The Absinthe Encyclopedia. Burgess Hill, UK: Oxygenee Press, 2009.
Wormwood Society Absinthe Association website. https://www.wormwoodsociety.org (accessed February 18, 2021).
By: Gwydion Stone