By Harold McGee
The miraculous thing about whipped cream is that simple physical agitation can transform a luscious but unmanageable liquid into an equally luscious but shapeable “solid.” Like foamed milk, whipped cream is an intimate intermingling of liquid and air, with the air divided into tiny bubbles and the cream spread out and immobilized in the microscopically thin bubble walls. Common as it is today, this luxurious, velvety foam was very laborious to make until 1900. Before then, cooks whipped naturally separated cream for an hour or more, periodically skimming off the foam and setting it aside to drain. The key to a stable foam of the whole mass of cream is enough fat globules to hold all the fluid and air together, and naturally separated cream seldom reaches that fat concentration, which is about 30%. It took the invention of the centrifugal separator to produce easily whipped cream.