Formerly the separation was made by the gravity method, allowing the cream to rise to the top of a pan and then skimming it off. C. G. de Laval of Sweden devised the first mechanical cream separator c.1880, based on the principle of centrifugal force.
Whole milk is conducted into a bowl, commonly through a central tubular shaft.
A spindle rotates the bowl at a rate of from 6,000 to 9,000 rpm, and a series of identical conical disks separates the milk into vertical layers. The heavier skim milk collects on the outer circumference of the rapidly whirling bowl, and the lighter cream tends to remain in the center. The pressure of the whole-milk supply above the bowl then forces the cream and skim milk out of the machine and into separate collecting vessels. Since the latter process is much faster than the gravity method, there is less chance for harmful bacterial action. Listing from Electric Library , a pay service.