My mistake was assuming that the buttermilk I had ordered would be the same kind of buttery buttermilk that Laura Ingalls Wilder had drunk in the late 19th century. This was a bad assumption. What we call buttermilk today has nothing at all to do with butter. In fact, the stuff known as cultured buttermilk at your local supermarket—i.e. milk that has been deliberately soured—is a 20th-century invention, and the product of a health-food diet craze dating back to the flapper era.
The distinction has to do with the lack of refrigeration in the days when people made their own butter. Sometimes the milk would be good; other times it had soured over the time it took to churn, or maybe it started out sour. Read the rest of the story at Slate. Link -via Metafilter
(Image credit: Organic Valley)