Separation of cream from full cream milk using the Disc- Bowl Centrifuge. Introduction:- Cream is usually a dairy product containing high fat percent, which can be seen floating on the top before the homogenization process. When the milk is unhomogenized, overtime, the fat lighter in weight rises to the top.
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The process in the industries is completely different as they use centrifuges, normally called as separators to accelerate the creaming process. Cost of cream totally depends upon its fat content.
Cream usually produced by the livestock grazing process on natural pastures normally contains some amount of natural carotenoid pigments acquired from plant materials they consume; as a result of which the cream appears a bit yellowish in colour. Cream derived from the milk of livestock fed indoors is usually white in colour as they normally are grain based pellets. There is a formula for determining the rate of sedimentation, widely known as Stokes’ law. It states that a particle moving through viscous liquid attains a constant velocity or sedimentation rate. Equation for Stokes’ law Vg = d2 (Pp- P1)/ 18 µ ?
G Where:- Vg = Sedimentation Velocity d2 = particle Diameter Pp = Particle density P1 = Liquid density G = gravitational acceleration µ = viscosity of liquid Aims:- 1. To separate cream from full cream milk at two speed settings of the disc bowl centrifuge. 2. To evaluate sensory properties of the cream and skimmed milk. 3. To determine the throughput of the centrifuge. Materials and Equipments:- Disc-bowl centrifuge 1 Litre and 400 ml beakers Litre measuring cylinder Sample cups –transparent 2 Litres full cream milk Large Plastic bowls Pans Stopwatch Digital Thermometer Method:- 1.
Two batches of 1 litre of full cream milk was warmed at 37 degree C. 2. 1 litre beaker was placed beneath the lower, heavy phase, spout of the centrifuge. This usually was the point from where the skim milk exits. Right after then the 400 ml beaker was placed beneath the upper, light phase, spout of the centrifuge which usually was the exit point for the cream. 3. Before carrying out the next step, it was ensured that the tap of the milk receiving reservoir at the top of the centrifuge was in a closed position ie. Pointing N to S 4. Warmed milk weighing 1 litre was then inserted into the reservoir. . The motor was switched on as soon as milk was inserted and was set on the lowest speed setting by adjusting the speed setting knob. 6. As the motor speed was steady, the tap of the reservoir containing milk was then released and the stopwatch was started. 7. Portions at light and heavy liquid phases were then collected from the relevant spouts, cream and skimmed milk respectively. 8. The stopwatch was switched off as soon as the milk reservoir was empty and the time taken was noted. 9. The motor of the centrifuge was allowed to run till the flow of skimmed milk and cream was ceased. 10.
The portions of skimmed milk and cream received through their relative phases were then measured and then the yield was calculated. 11. The throughput of the material was then determined in litres per hour at its respective speed setting. 12. The stages 2 to 12 were repeated using second batch of warmed milk, with the only difference being the time setting. The whole process was carried out by operating the motor on the highest speed setting. 13. The above process was followed by placing the large bowl underneath the spouts and by flushing the centrifuge using cold water just to clear the washings in the centrifuge. 4. Right after the process the whole equipment was dismantled including the reservoirs spouts, collecting funnel etc. The parts were then washed using hot water with a little detergent. 15. The cream and skimmed milk from each speed setting (i. e. High speed setting and low speed setting) were then subjected to sensory properties evaluation. * * * * Result:- * * The following were the results obtained :- 1. The results for 0. 1 % skimmed milk at low speed setting were * Fat:- 00. 07% * * And the results for same product at high speed setting were * Fat:-00. 03% * 2.
The results for 2 % semi skimmed milk at low speed setting were * Fat:- 1. 60 % * * The results for 2 % semi skimmed milk at high speed setting were * Fat:- 1. 64% * 3. The results for 4% Whole milk at low speed setting were * Fat:- 6. 56% * * The results for 4% Whole milk at High speed setting were * Fat:- 7. 25% * * * Discussion:- * 1. Principles of the operation of Disc-bowl Centrifuge. * Brennan (2006) states that the Disc bowl centrifuge works on the principle of particle density. Feed is introduced through the bottom of the bowl.
As it comes with the contact of the centrifugal force, the dense phase moves downside while the lighter phase passes through the top spout. * 2. Different Categories of cream available to the consumer and their legal minimum fat contents? * Sheila (2006) mentioned in an article that categories of cream available are * Single cream – 18 % minimum fat content * Double cream – 48% minimum fat content * Half cream – 12% minimum fat content * Whipping Cream – 35% minimum fat content * Creme fraiche – 30% minimum fat content * Soured cream – 18% minimum fat content * Clotted cream – 55% minimum fat content. 3. Categories of cream produced in the Practical? * Type of cream produced in the practical was single cream * 4. Purpose of Cream screw? * The thickness of the cream can be adjusted by the help of the cream screw. Cream screw helps to trap the cream and helps the cream to let out. * * 5. Why is the milk heated first? * De (1991) explained that, higher the temperature and degree during agitation the greater is the loss of skimmed milk and vice versa. When the milk is heated and agitated, the agitation process causes size reduction of bigger fat globules into smaller ones.
As a result of which they escape the effect of centrifugal force, leading to exclusion of fat loss in the skimmed milk. To reduce creaming. * * Conclusion:- * Cream was successfully separated from the milk using Disc bowl centrifuge. The cream was further tested for its sensory properties, and the sensory properties of the cream were found to be appealing. * * * * References:- * * J. G. Brennan (2006). “Food Processing Handbook”. Wiley-Vch. * * Sheila (2006). “Cream Final Edition”. The Times, London, UK. * * Sukumar De (1991). “Outlines of Dairy Technology”. Oxford University Press.