How a cream separator splits milk

Fat globules are lighter than the watery skim milk around them, so in a jug cream slowly rises over many hours. A separator spins milk in a bowl full of conical discs at thousands of rpm, multiplying the effective gravity thousands of times, so light fat streams inward and up to the cream outlet while heavier skim milk flows outward and out the skim outlet, in seconds.

Controls

Labels

Animation speed

Bowl speed

Fat globule diameter

Step through it

Milk inWarm whole milk flows down a central pipe into the spinning bowl. Separating warm milk works better because the skim is less viscous.
The disc stackDozens of thin cones are stacked with gaps of a fraction of a millimeter. Each gap is a tiny settling channel, so a globule only has to travel a short way.
Light goes in, heavy goes outSpinning pushes the denser skim milk outward. The lighter fat globules are squeezed inward toward the axis and rise to the cream outlet.
Slower spinAt 2,000 rpm the force drops to under a seventh of normal. Small globules cannot cross their gap before the flow carries them out with the skim.
Two streams outSkim and cream leave through separate outlets. Under normal settings roughly 90 percent comes out as skim and 10 percent as cream.

Centrifugal acceleration

A spinning bowl creates an acceleration of omega squared times r, where omega is the spin rate in radians per second and r is the distance from the axis. Divided by g, it says how many times stronger than gravity the separating force is. At 5,400 rpm and 20 cm it is about 6,500 times gravity.

The scene spins far slower than the real bowl so you can follow it.

Try it: set the globule to 1 µm and the speed to 3,000 rpm. Crossing one disc gap now takes several seconds, so small globules escape into the skim. Raise the speed to 7,000 rpm and the time drops more than fivefold.

Stokes settling

A small sphere in a viscous liquid moves at Stokes' speed: v = 2/9 x radius squared x density difference x acceleration / viscosity. The model uses a density difference of 110 kg/m³ between skim and fat and a skim viscosity of 1.5 mPa·s, rounded teaching values. Because speed grows with the square of the radius, large globules separate easily and the smallest ones are the ones lost to skim.

Sources

Clarification and Cream Separation (Dairy Science and Technology eBook)University of Guelph
Cream separation in dairy industryINFLIBNET e-PG Pathshala (India)

How to cite this model

Avid Solutions International. (2026, November 11). How a cream separator splits milk [Interactive 3D model]. Avid Field Lab. https://avidsolutionsintl.com/explore/cream-separator

Last updated November 11, 2026

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