Separation efficiency (Es)

 - represents fat transferred from milk to cream 

Es = 1 - fs/fm 
where fs = skim fat as percent w/w
 fm = milk fat as percent w/w

Separation efficiency depends on initial milk fat content and residual fat in the skim. Assuming optimum operation of the separator, the principal determining factor of fat loss to the skim is fat globule size. Modern separators should achieve a skim fat content of 0.04 - 0.07%.