Just last week, I caught up with my friend over dinner and was introduced to the national beverage of Turkey: rakı (pronounced as rah-kuh). Knowing my friend, I gathered it’s probably an alcohol. No surprise there, Rakı has an alcoholic content of 40-45% and is usually served mixed with cold water. When this happens, the drink turns milky white and hence its nickname “lion’s milk”. This is known as the Ouzo effect.
Interestingly, this phenomenon is not just limited to rakı. Other drinks include Greece’s ouzo (from which the name is derived), France’s pastis, Italy’s sambuca and Eastern Mediterranean countries’ arak. These alcohols have one thing in common: they contain an essential oil called anethole. Anethole is usually extracted by steam distillation (see my previous post on Did you smell that?) from the anise plant native to Eastern Mediterranean region and Southwest Asia.
Anethole is a hydrophobic molecule and is insoluble in water. However, it is highly soluble in ethanol (a.k.a. the alcohol you love to drink). In short, it exhibits qualities of a typical teenager: water-hating but alcohol-loving.
In pure rakı, the anethole oil is soluble and dispersed in alcohol, and appears colourless. Adding water to the clear liquor decreases anethole’s solubility. Under such circumstance, the oil starts to form nano-size droplets (or nanodroplets) in the process known as nucleation, which will then gather to form bigger micro-size droplets. These micro-size droplets scatter light, resulting in the milky white appearance you see. The resultant mixture is known as an emulsion.
One interesting point to note is that the Ouzo effect is a spontaneous emulsification process and does not require the use of any surfactant, which is commonly required for the creation of emulsions. However, the underlying mechanism behind this phenomenon is still not fully understood and remains a subject of further research.
Nevertheless, by taking advantage of the Ouzo effect, researchers aim to prepare nanoparticles such as pharmaceutical organic compounds, and even nanocarriers for drugs. In other words, they are hopeful that this will potentially lead to applications in therapeutic drug preparation and drug delivery.
– Ling Ling
P.S. Şerefe means cheers in Turkish.
- Botet, R. (2012). The “ouzo effect”, recent developments and application to therapeutic drug carrying. Journal of Physics: Conference Series, 352, 12047. https://doi.org/10.1088/1742-6596/352/1/012047
- Lepeltier, E., Bourgaux, C., & Couvreur, P. (2014). Nanoprecipitation and the “Ouzo effect”: Application to drug delivery devices. Advanced Drug Delivery Reviews, 71, 86–97. https://doi.org/10.1016/j.addr.2013.12.009
- Zemb, T. N., Klossek, M., Lopian, T., Marcus, J., Schöettl, S., Horinek, D., … Kunz, W. (2016). How to explain microemulsions formed by solvent mixtures without conventional surfactants. Proceedings of the National Academy of Sciences, 113(16), 4260–4265. https://doi.org/10.1073/pnas.1515708113
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