dried milk- Specification, equipment, types

dried milk- Specification, equipment, types

1. Dried milks Dr. Zanwar S.R. Assistant Professor , MGM CFT , Gandheli FPT-238

2. Definition “Dried milk or milk powder is the product obtained by the removal of water by heat or the suitable means, to produce a solid containing 5 % or less moisture. The dried product obtained from whole milk is called Dried whole milk or whole milk powder (WMP); and that from skim milk is known as Dried Skim Milk or Skim Milk Powder (SMP), or Non-fat Dry Milk (NFDM).

3. PFA Legal Standards Whole Milk Powder “According to the PFA Rules, (1976), whole milk powder is the product obtained from cow or buffalo milk, or a combination thereof, or from standardized milk, by the removal of water. It may contain calcium chloride, citric acid and sodium citrate, sodium salts of ortho phosphoric acid and poly phosphoric acids, not exceeding 0.3 % by the weight of the finished product. 0.01 % of butylated hydroxy anisole (by weight) of the finished product. Milk powder should contain not more than 5.0 % of moisture and not less than 26.0 % of fat. The total acidity expressed as lactic acid should not be more than 1.2 %. The  standard plate count may not exceed 50,000/g and the  Coliform count may not exceed 90/g. The maximum solubility index should be 15.0 for roller dried and 2.0 for a spray dried product.

4. Skim Milk Powder “According to the PFA Rules, (1976), skim milk powder is the product obtained from cow or buffalo milk, or a combination thereof, by the removal of water. It may contain calcium chloride, citric acid and sodium citrate, sodium salts of ortho phosphoric acid and poly phosphoric acids, not exceeding 0.3 % by the weight of the finished product. Skim milk powder should contain not more than 1.5 % of fat and the moisture may not exceed 5.0 %. The total acidity expressed as lactic acid should not be more than 1.5 %. The  standard plate count may not exceed 50.000/ g. and the  Coliform count may not exceed 90/g. The maximum solubility index should be 15.0 for roller dried and 2.0 for a spray dried product .

5. Characteristics Whole milk powder Skim milk powder Flavor & odor Good Good Moisture (%) 4 5 Total milk solids(%) 96 95 Solubility Solubility index (ml) 15(roller dried) 15 (roller dried) 2 (spray dried) 2 (spray dried) Solubility (%) 85 ml (roller dried) 85 ml (roller dried) 98.5 ml (spray dried) 98.5 ml (spray dried) Fat (%) Not less than 26 Not more than 1.5 Titratable acidity (%) 1.2 1.5 Bacterial count per g. (max) 50000 50000 Coliform count per g (max) 90 90

6. Classification of Dried Milk

7. Milk drying systems Two types of drying: Drying by Cold Treatment Drying milk by freezing out the water and centrifuging. Drying milk by freezing and sublimation: This freeze-drying method, consists of freezing the product and supplying heat, so that moisture is removed by sublimation by maintaining a vacuum in the vaporizing chamber. Drying by application of heat Roller/Film/Drum drying (atmospheric or vacuum) Spray drying (compressed air, pressure spray, centrifugal disc) Dough or paste drying Foam drying Fluid bed drying.

8. Film/Drum/Roller Drying Principle: The product to be dried is applied in a thin layer (film) onto the surface of one or two steam heated drums by using different application systems. The temperature on the drum surface is above 100ºC, and heat can be transferred rapidly to the product. The principle of the roller drying process is that milk is applied in a thin film upon the smooth surface of a continuously rotating steam heated metal drum. The film of dried product is continuously scraped off by a stationary knife located opposite the point of application of the milk. The drier may consist of a single drum or a pair of drums (double drum). The milk may be pre-concentrated before it is being applied to the drum, and the degree of concentration varies with the design of the dryer. The dried milk film is milled to break up the film. The particles of a roller drier powder are solid, flat, irregular flakes containing no air. The absence of occluded air retards oxidation, resulting in good keeping quality.

9. Advantages Relatively low capital and operating costs Plant is movable and occupies little floor space Plant is easy to handle Suitable for operating small quantities of milk economically Produces milk of better keeping quality Disadvantages Produces milk powder with low solubility Produces a definitely cooked/scorched flavor in the reconstituted milk

10. Fig: Single and double drum drier

11. Spray drying Spray drying can be described as the instantaneous removal of moisture from a liquid. To achieve this, the liquid is converted into a fog-like mist ( atomised ), whereby it is given a large surface. The atomised liquid is exposed to a flow of hot air in a drying chamber. The air has the function of supplying heat for the evaporation and, in addition, it acts as carrier for the vapour and the powder. When the atomised product is in contact with the hot air, the moisture evaporates quickly and the solids are recovered as a powder consisting of fine hollow spherical particles with some occluded air. Exhaust air is removed on the side and passes through cyclones and filters (where entrained powder particles are separated and recovered). Automization : to reduce the milk particles so small in size & produce mist. Three methods of automizing pressure jet/nozzle, centrifugal disc, compressed air Heating air : temperature of heating air is 149-260 o C & at outlet it ranges from 100- 105 o C. Product recovery : separation of air & powder, separation of large particles (gravity), separation of fines (filter bag dust collector, cyclone separator, liquid dust collector).

12. method of manufacture by drum process of wmp & smp Receiving milk   Preheating (35-40 o C)   Filtration/clarification (35-40 o C)   Standardization   Forewarming (85 o C/10 min)   Condensing   Homogenization (2 stage @ 63-77 o C)   Preheating (74-85 o C)   Drum drying   Packaging   Storage

13. Drum drier Receiving of milk : only high grade milk. Filtration/clarification : to remove extraneous matter. Standardization : it is done to adjust ratio of fat & SNF in raw milk. Forewarming : for destruction of microbes & inactivation of enzymes. Condensing : total solids 16-18% in condensed milk. Homogenization : the whole milk is homogenized after concentration to reduce proportion of free fat which lowers down chances of oxidation. Preheating : increases efficiency of roller driers. Drum drying : as described above.

14. Method of manufacture by drum process of WMP & SMP

15. Spray Drier All stages same as roller drier Condensing : A concentration of 35-45% total solids is produced. Spray drying : The concentrated milk is spray dried with inlet air at 143 to 232 o C & exit air at 74 to 93 o C. Sifting : A 12 mesh screen is used for sifting dry whole powder & 25 mesh screen for skim milk powder. Storage: At room temperature.

16. Packaging Use of foil laminated paper. Fibreboard carton with an inner lining of foil laminated to paper. A polyethylene bag with fibreboard . Tin can Plastic coated paper bags.

17. storage Power can be stored at high temperature but temperature lower than 24 C are desirable. Instantization : It refers to the process by which dried milk & milk products are made instant soluble.

18. Defects in WHM and SMP with causes and prevention