When: September 26
National Key Lime Pie Day celebrates Florida's official state pie — a custard made from Key lime juice, egg yolks, and sweetened condensed milk in a graham cracker crust. It's a pie invented partly out of necessity in the Florida Keys, where fresh dairy was scarce but canned condensed milk was shelf-stable.
The original Key lime pie doesn't require baking — the acid in Key lime juice chemically "cooks" the egg yolks and sweetened condensed milk through a process called acid denaturation.
Key lime pie was born of necessity in the Florida Keys, where the isolation of the island chain made fresh dairy and refrigeration unreliable well into the 20th century. Sweetened condensed milk — invented by Gail Borden in the 1850s and made shelf-stable without refrigeration — became a pantry staple in the Keys. When combined with the acidic juice of the small, seedy Key limes (Citrus aurantiifolia) that grew prolifically throughout the region, it created a filling that required no cooking: the acid denatures the egg proteins and thickens the condensed milk through a chemical reaction. The pie's invention is attributed by legend to "Aunt Sally," the cook for Florida sponge magnate William Curry in the late 19th century. While this is likely folk myth, recipes for Key lime pie began appearing in print in the early 20th century, and the dish is documented in Keys culture by the 1930s. The Overseas Highway connecting the Keys to the mainland wasn't completed until 1938, which helps...