The chemistry of milk washing, aka the secret to Ben Franklin’s favorite tipple

It’s well-known that Benjamin Franklin was a Founding Father who enjoyed a nice tipple or two (or three). One of his favorite alcoholic beverages was milk punch, a heady concoction of brandy, lemon juice, nutmeg, sugar, water, and hot whole milk—the latter nicely curdled thanks to the heat, lemon juice, and alcohol. It employs a technique known as “milk washing,” used to round out and remove harsh, bitter flavors from spirits that have been less than perfectly distilled, as well as preventing drinks from spoiling (a considerable benefit in the 1700s).

Some versions of milk punch also incorporate tea, and in the mixed drink taxonomy, it falls somewhere between a posset and syllabub. The American Chemical Society’s George Zaidan decided to delve a bit deeper into the chemistry behind milk washing in a new Reactions video after tasting the difference between a Tea Time cocktail made with the milk washing method and one made without it. The latter was so astringent, it was “like drinking a cup of tea that’s been brewed for 6,000 years,” per Zaidan. In the process, he ended up stumbling onto a flavorful new twist on the classic espresso martini (although martini purists probably wouldn’t consider either to be a true martini).

There isn’t anything in the scientific literature about milk washing as it specifically pertains to cocktails, so Zaidan broke the process down into three simple experiments, armed with all the necessary ingredients and his trusty centrifuge. First, he combined whole milk with Coke, a highly acidic beverage that curdles the milk. Per Zaidan, this happens because of the casein proteins in milk, which typically have an overall negative charge that keeps them from clumping. Adding the acid (Coke) adds protons to the mix so that it is electrically neutral (usually at a pH of 4.6).