Dr. Mohammad Ashraf Paul

Division of Livestock Products TechnologyFaculty of Veterinary Sciences & Animal Husbandry SKUAST-K Alusteng, Ganderbal Kashmir

Water in a liquid product – in this case milk concentrate is removed, so that the product takes on a solid formMicroorganisms are unable to reproduce at such a low water content thus shelf life of the milk is extended Reduces weight and volume Reduces the cost of transporting and storing the product.Skim milk powder has a maximum shelf life of about three years while whole milk powder has a maximum shelf life of six months. Because the fat in the powder oxidises during storage, with consequent deterioration in flavour. However, the shelf life can be extended by using appropriate packaging technology i.e. packing the powder under an inert gas such as N2

Dehydration : Near complete removal of water from milk to a < 5% level.

Dehydration /Desiccation Methods‘According to Marco Polo’s accounts of his travels in Asia, Mongolians

produced milk powder by drying milk in the sun’

Cold Methods: Freezing out water & centrifuging Freezing milk & Sublimation • Produces very high quality powder• Product is deep-frozen and the water frozen in the product is

evaporated under vacuum• Ensures high product quality as, among other things, no protein

denaturing takes place compared to drying milk at higher temperatures where the proteins are denatured to a greater or a lesser extent

• Freeze-drying is not widely used for the production of milk powder because of the high energy demand.

Hot Methods: Film ,roller or drum drying Less common ,used for a few special products Spray drying In spray drying, the milk is first concentrated by evaporation and then dried in a spray towerAlthough there are many types of driers, spray driers are the most widely used type of air convection drier. It turns out more tonnage of dehydrated products than all other types of driers combined. It is limited to food that can be atomized, i.e. liquids, low viscosity pastes, and pureesDrying takes place within a matter of seconds at temperatures approximately 200° C. Evaporative cooling maintains low product temperatures, however, prompt removal of the product is still necessary

Principal components include:• High pressure pump for introducing liquid into the tower• Device for atomizing the feed stream• Heated air source with blower• Secondary collection vessel for removing the dried food from the airstream•Means for exhausting the moist airAtomizers :Provide a large surface area for exposure to drying forces:1 litre = 12 billion particles = >300 ft 2 (30m2)i. Compressed airii. Pressure spray iii. Centrifugal disc

Rotary disc

Pressure nozzles /Two- fluid nozzle

Powder Recovery systems:

•Bag filters- very efficient (99.9%)

•Cyclone collector- efficient (99.5%)

•Wet scrubber- the most economical outlet air cleaner. The principle of a wet scrubber is to dissolve any dust powder left in the airstream into either water or the feed stream by spraying the wash stream through the air. This also recovers heat from the exiting air and evaporates some of the water in the feed stream

Two and Three Stage Drying Processes•In single stage spray drying, the rate of evaporation is high in the first part of the process, and it gradually decreases because of the falling moisture content of the particle surfaces• In order to complete the drying in one stage, a relatively high outlet temperature is required during the final drying phase resulting in high particle temperature and thus heat damage .•Two stage drying process - is superior to the traditional single stage drying in terms of product quality and cost of production.• consists of a spray drier with an external vibrating fluid bed placed below the drying chamber. •The product can be removed from the drying chamber with a higher moisture content, and the final drying takes place in the external fluid bed where the residence time of the product is longer and the temperature of the drying air lower than in the spray dryer.

Three stage drier: Here second stage is a fluid bed built into the cone of the spray drying chamber(integrated fluid bed). Thus it is possible to achieve an even higher moisture content in the first drying stage and a lower outlet air temperature from the spray drier. • The inlet air temperature can be raised resulting in a larger temperature difference and improved efficiency in the drying process. •The exhaust heat from the chamber is used to preheat the feed stream. •The third stage is again the external fluid bed, for final drying and/or cooling the powder. The results are as follows:oHigher quality powders with much better rehydrating properties directly from the drier oLower energy consumptionoIncreased range of products can be spray driedoSmaller space requirements

Roller drying Process summary: Atmospheric / Vacuum

Milk concentrate

Adjustable pump

Feeding

Drying drum

Drying drum cont.

Scraper(Doctors blade)

Grinder

Sifter

Dried product

Spray drying-Process summary:

•The liquid food is generally preconcentrated by evaporation to economically reduce the water content•The concentrate is then introduced as a fine spray or mist into a tower or chamber with heated air. •As the small droplets make intimate contact with the heated air, they flash off their moisture, become small particles, and drop to the bottom of the tower and are removed. •The advantages of spray drying include a low heat and short time combination which leads to a better quality product.

Skim Milk Powder manufactureReceiving milk

Cooling@ 50C

Preheating (350C) Separation

Pasteurization (710C /15s)

Low heat SMP High heat S M P Condensing

Reheating (630C)

Filtration Pumping (3000 psi) Spray drying (850C outlet air)

Cooling (320C) Sifting (25 mesh ) Packaging & storage @ RT

Low heat SMP.. High heat SMP

Preheating 850C/20min.

Condensing

Reheating(740C)

Remaining steps same

as for LowHeat SMP

Whole Milk Powder Standardization

Fat/SNF=1:2.77

Preheating(710C)

Filtration/Clarification

Homogenization2500 psi/63-740C – I ; 500psi-II

Heating (930C/3min.)

Condensing

Preheating710C

Pumping (2500psi)

Spray Drying (820C outlet temp.)

Cooling (320C)

Sifting

Vacuum+N2

Packaging & Storage @RT

Instantiation : Process of making dried milk products instant –soluble. Process:1. Wetting of particle surface (steam,

atomized water or both in a tube or chamber or cyclone

2. Agglomeration (particles collide with each other due to turbulence and adhere to form clusters)

3. Re drying – with hot filtered air 4. Cooling5. Sizing to exclude very large

agglomerates & very small particles 6. Sifting & packaging.

PFA Standards:• WMP :

• A product obtained from cow or buffalo milk, or a combination thereof , or from standardized milk, by the removal of water. It may contain Cacl2 ,Citric acid and sodium citrate , sodium salts of orthophosphoric acid and poly phosphoric acids , not exceeding 0.3% by weight of the finished product , and 0.01% of BHA(by Wt.) of the product. Such addition need not to be declared on the label. Milk powder should contain not more than 5% moisture and not less than 26% fat. The total acidity expressed as lactic should not be more than 1.2%.The SPC may not exceed 50000/g and coliform count may not exceed 90/g. Max. solubility index should be 15.0 for a roller dried and 2.0 for spray dried product.

• SMP :• Fat Not more than 1.5% ; TA,1.5%

Various uses of milk powder : • Recombination of milk and milk products • Reconstituted Milk and milk products • In the bakery industry to increase the volume of bread and improve its water-binding capacity. The bread will then remain fresh for a longer period of time • Substitute for eggs in bread and pastries • Producing milk chocolate • Producing various types of ready-cooked foods in food and catering trade • In baby foods • Production of ice cream • Animal feed, calf growth accelerator, pharmaceuticals,microbiological media preparations

Typical properties of spray-dried milk powder :

Characteristics WMP SMP

Solubility (ml) 0.1 – 0.5 0.1 – 0.5

Scorched particles A A (standard disc grading)

Residual moisture (max.%) 3.0 4.0

Bulk density(g/ml) 0.45 – 0.57 0.45 – 0.6

Total spore count (max. n/g) 10 000 10 000

Composition of milk powder Characteristics Whole milk Skim milk

Fat, % solids content 26 – 29 1.25

Protein, % solids content 25 – 27 34 – 38

Lactose, % solids content 35 – 38 48 – 56

pH 6.6 – 6.7 6.6 – 6.7

Acid value, % < 0.16 < 0.16

Total spore count, n/ml 10 000 10 000