Dehydration Of Milk 1m2f5z

Dehydration / Desiccation Dr . Mohammad Ashraf Paul Division of Livestock Products Technology Faculty of Veterinary Sciences & Animal Husbandry SKUAST - K Alusteng , Ganderbal Kashmir

Dehydration : §Near complete removal of water from milk to § a < 5 % level . §Water in a liquid product – in this case milk concentrate is removed , so that the product takes on a solid form §Microorganisms 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

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Dehydration /Desiccation Methods

‘According to Marco Polo’s s of his travels in Asia, Mongolians produced milk powder by drying milk in the sun’

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Cold Methods: v Freezing out water & centrifuging v 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 

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 tower §Although 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 purees §Drying takes place within a matter of seconds at temperatures approximately 200 ° C . §Evaporative cooling maintains low product temperatures , however , prompt removal of the

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 air

Atomizers :

Provide a large surface area for exposure to drying forces : 1 litre = 12 billion particles = > 300 ft 2 (30m 2 )

i. Compressed air Rotary disc ii. Pressure spray iii. Centrifugal disc

Pressure nozzles Two - fluid nozzl

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 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

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 consumption oIncreased range of products can be spray dried oSmaller space requirements

Roller drying Process summary:

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Atmospheric / Vacuum

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Milk concentr ate 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 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 .

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Skim Milk Powder manufacture Receiving milk

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Cooling@ 50C 

Preheating (350C) â  Separation â Pasteurization (710C /15s) â 

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Low heat SMP High heat S M P

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â Condensing 

L o w h e a t S M P. . â High heat SMP â 

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Reheating (630C)

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P re h e a tin g 8 5 0 C / 2 0 m in .

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Filtration

â C o n d e n sin g â R e h e a tin g ( 7 4 0 C ) â R e m a in in g ste p s sa m e

Whole Milk Powder S ta n d a rd iz  a tio n 

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Fat / SNF = 1 : 2 . 77

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Preheating (71 0 C )

Filtration / Cl arification Homogenizati on

2500 psi / 63 - 74 0 C – I ; 500psi - II

Heating (93 0 C / 3min .) Condensing

Preheating71 0 C Pumping ( 2500psi ) Spray Drying

(82 0 C outlet temp .)

Cooling (32 0 C ) Sifting Vacuum + N 2 Packaging & Storage @RT

Instantiation :

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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. Cooling 5. Sizing to exclude very large agglomerates & very small particles 6. Sifting & packaging. 

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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 orthophosphoricacid 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.

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 Solubility (ml)

WMP

SMP

0.1 – 0.5

0.1 – 0.5

Scorched particles ( standard disc grading )

A

A

Residual moisture ( max .%)

Bulk density ( g / ml )

4.0 0 . 45 – 0 . 57

3.0

Composition of milk powder Characteristics milk

Fat , % solids content

Whole Skim milk 26 – 29 1 . 25

Protein , % solids content 25 – 27 34 – 38 Lactose , % solids content 35 – 38 48 – 56 pH 6.7

6.6 – 6.7

6.6 –