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How are bottle centrifuges used to test the butterfat content of milk?

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tubular centrifuge — centrifuge Figure 1: Tubular centrifuge

Bottle centrifuges are used as standard laboratory equipment to test the butterfat content of milk, a process distinct from the continuous industrial separation of cream from milk performed by disk-type centrifuges.12

The specific method for measuring butterfat, known as the Babcock test, was developed by agricultural research chemist Stephen Moulton Babcock in 1890. In a bottle centrifuge, milk samples are placed in "bottle-type" containers that are symmetrically mounted on a vertical shaft. When the centrifuge spins, the resulting centrifugal force causes sedimentation in a radial direction, allowing for the precise measurement of butterfat components within the sample. This testing procedure was instrumental in discouraging milk adulteration and improving dairy production standards.31