When: September 12
National Chocolate Milkshake Day on September 12th celebrates one of America's most beloved cold drinks — a thick blend of chocolate ice cream and milk that has evolved from an alcoholic Victorian tonic to a soda fountain staple to the fast food milkshake consumed by millions. The science of what makes a milkshake "thick" and why some milkshakes taste so much better than others is genuinely interesting.
The original "milkshake" from the 1880s contained whiskey — the non-alcoholic version didn't become the mainstream format until the 20th century, when health messaging shifted the drink toward ice cream.
The word "milkshake" appeared in print in 1885 describing a drink made with eggs, whiskey, and milk — a tonic recommended for medicinal purposes. By the turn of the century, the term had shifted to non-alcoholic drinks. The modern milkshake — ice cream blended with milk — became possible with the electric blender and the growth of soda fountain culture. Hamilton Beach introduced its malt-o-mixer in 1911, making it practical for soda fountain workers to produce the drink quickly. A blended, cold ice cream drink was one of the soda fountain's defining products by the 1920s. The physics of the milkshake are more interesting than they appear. "Thickness" is determined primarily by the density of the ice cream used — low-overrun, dense ice cream (more cream, less air) produces a shake that holds its structure; high-overrun ice cream (more air, cheaper) produces a thinner, faster-melting result. Blending time works in the opposite direction from what most people expect: longer blending...