cream separator, dairy machine used to separate fresh whole milk into cream and skim milk. 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. The cream separator makes it possible to control the amount of fat (called butterfat) remaining in the milk. The gravity method ordinarily leaves one fourth of the fat in the milk, while the cream separator leaves only 0.01% to 0.02% of the fat in the skim milk. Since the latter process is much faster than the gravity method, there is less chance for harmful bacterial action.