Etiket Arşivleri: Cream Separation

Cream Seperation ( Prof. S K Dash )

CREAM SEPARATION

(Cream separation, Centrifugation, Tubular bowl centrifuge, Disc bowl centrifuge, Domestic cream separator)
The cream separation is a very important unit operation in dairy industry. The cream or fat is taken out of milk for standardisation purpose. Besides, cream is also required to prepare some value added products as ghee, butter, etc. Cream is usually separated from milk by the centrifugation process.

Centrifugation

Sometimes gravity separation may be too slow because of the closeness of densities of the particle and the fluid, or because of the association forces holding components together, as in emulsions like whole milk. In that case centrifugation helps in separation of the components on the basis of differences in their densities.
• The centrifuge increases the forces on particles many fold.
• Thus the particles that do not settle readily or at all in gravity settlers can often be separated from fluids by centrifugal force.
• The relative settling velocities of small particles are not changed, but the disturbing effects of Brownian motion and free convection currents are overcome.
The equipment using this principle of separation is known as a centrifuge. The
centrifuges are used for:
• separation of immiscible liquids,
• clarification of liquids by removal of small amounts of solids, and
• for removal of solids from liquids
Centrifuges are also used for centrifugal filtration, where the centrifugal force is used (not the pressure difference) to separate the solids through a filter medium. The major applications of the centrifuges are shown in Fig. 8.1.

Cream Separation

Milk is an oil-in-water emulsion, with the fat globules dispersed in a continuous skimmilk phase. If raw milk were left to stand, however, the fat would rise and form a cream layer. Homogenization is a mechanical treatment of the fat globules in milk brought about by passing milk under high pressure through a tiny orifice, which results in a decrease in the average diameter and an increase in number and surface area, of the fat globules. The net result, from a practical view, is a much reduced tendency for creaming of fat globules. Three factors contribute to this enhanced stability of homogenized milk: a decrease in the mean diameter of the fat globules (a factor in Stokes Law), a decrease in the size distribution of the fat globules (causing the speed of rise to be similar for the majority of globules such that they don’t tend to cluster during creaming), and an increase in density of the globules (bringing them closer to the continuous phase) oweing to the adsorption of a protein membrane. In addition, heat pasteurization breaks down the cryo-globulin complex, which tends to cluster fat globules causing them to rise.

Cream Separation, Churning & Homogenization

Purpose of the experiment:

The aims are:

• to separate cream from milk and to obtain milk fat by application of churning process.

• to show how homogenization works

• to produce butter and pure fat using churning.

CLARIFICATION AND CREAM SEPARATION

The following topics will be covered in this section:

• Centrifugation

• Separation

• Clarification

• Standardization