Dairy Chemistry And Biochemistry

MILK LIPIDS 111

Figure 3.21 (Continued),

3.10.2 Mechanical separation of milk

Gravity creaming is relatively efficient, especially in the cold (a fat content

of 0.1% in the skim phase may be obtained). However, it is slow and

inconvenient for industrial-scale operations. Mechanical milk separators

were developed independently in the 1880s by Alpha and Laval; schematic

representations of a modern separator are shown in Figures 3.21 and 3.22.

In centrifugal separation, g in Stokes' equation is replaced by centrifugal

force, wZR, where w is the centrifugal speed in radianss-' (2n radi-

ans = 360") and R is the distance (cm) of the particle from the axis of

rotation.

where S is the bowl speed in r.p.m. Inserting this value for g into Stokes'
equation and simplifying gives:

O.O0244(p - pz)rZS2R
rl
Thus, the rate of separation is influenced by the radius of the fat globules,
the radius and speed of the separator, the difference in density of the
continuous and dispersed phases and the viscosity of the milk; temperature
influences r, (pi - p2) and q.

V=