(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.
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.
Q.1) (a) Answer any THREE questions
a) Define Cream, mention normal minimum percentage of milk fat. list four constituent of fresh cream
b) List four different types of butter, write two properties of each
c) Describe the term ultra high temperature pasteurization.
d) List eight constituent and its approximate concentration which indicate milk quality.
Q.1) (b) Answer any ONE questions
a) Describe the term ‘the vacreation process”
b) Explain with reason the fat losses during butter making.
Q.2) Answer any FOUR questions
a) Describe separation of cream by gravity method and centrifugal method.
b) Comment on clean milk production.
c) Give eight merits of homogenized milk.
d) Give eight flavour defects in milk and prevention.
e) List four different types of cream available in market.
f) Define rehydrated milk, give two merits of rehydrated milk
Q.3) Answer any FOUR questions
a) Give four characteristics of fermented milk and its products.
b) List additives permitted to be use in butter and the role in it.
c) What is irradiated milk?
d) List eight micro-organisms beneficial to the dairy industry.
e) Mention three steps after filtration in toned milk and write appropriate temperature.
Q.4) (a) Answer any THREE questions
a) Write four types of milk available in market and give two characteristic of each.
b) How can spoilage of milk between reception and storage be reduced.
c) Draw flow diagram of recombined milk.
d) Give four defects in butter and how can prevent these defect in butter.
Q.4) (b) Answer any ONE questions
a) What is the action of milk on metal?
b) Explain in details continuous butter making process.
Q.5) Answer any TWO questions
a) List four microbiological factor related to milk, give example of each.
b) Draw a flow diagram to show manufactured of flavoured milk write the function of each step in four lines.
c) Give four defects in cream, their causes and prevention.
Q.6) Answer any FOUR questions
a) Give eight uses of butter.
b) Write two physical and two chemical properties of cream. State its effect on quality of cream.
c) Why HTST method is more useful in milk industry than other method. Give four reason.
d) List which stabilizer is used in flavoured milk. State its two properties.
e) Give four adulterants in butter.
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:
Homogenisation, which breaks the milk fat globules into smaller globules that do not rise to form a cream layer during sterilization or shipping. Consequently, it diminishes creaming and may also diminish the tendency of globules to clump or coalesce. Separation of elements in a mixture of materials having different specific gravity such as cream and skim milk is achieved by special rotating machines, which are called centrifugal cream separator. Separated cream is agitated in churn in order to get butter by changing the emulsion from oil in water to water in oil.
The production of beverage milks combines the unit operations of clarification, separation (for the production of lower fat milks), pasteurization, and homogenization. The process is simple, as indicated in the flow chart. While the fat content of most raw milk is 4% or higher, the fat content in most beverage milks has been reduced to 3.4%. Lower fat alternatives, such as 2% fat, 1% fat, or skim milk (<0.1% fat) or also available in most markets. These products are either produced by partially skimming the whole milk, or by completely skimming it and then adding an appropriate amount of cream back to achieve the desired final fat content. Vitamins may be added to both full fat and reduced fat milks. Vitamins A and D (the fat soluble ones) are often supplemented in the form of a water soluble emulsion to offset that quantity lost in the fat separation process.