3. SPRAY DRYING
Spray drying is a method of producing a dry powder from a liquid or slurry by
rapidly drying with a hot gas
4.
5.
6. Collection
Milk is mostly collected in insulated tankers transferred to processing units
Raw milk on arrival at the factory is rapid tested for
Temperature
Hygiene
Antibiotics
Water addition
Adulteration
On acceptance
The milk is pumped into a silo storage tank at the processing plant
Held at temperatures below 7 C and usually below 5 C.
7. Separation & Standardization
In Preheating, standardized milk is heated to temperatures between 75 and 120C
For a specified time
Preheating causing
Denaturation of whey protein
Destroys bacteria
Inactivates enzymes
8. Pasteurization
The milk is high temperature short-time pasteurized (HTST) by
Heating at 72 C for 15 seconds
9. Preheating
In Preheating, standardized milk is heated to temperatures between 75 and 120C
For a specified time
Preheating causing
Denaturation of whey protein
Destroys bacteria
Inactivates enzymes
10. Evaporation
Boiling the milk under a vacuum at temperatures below 72C in a falling film on the inside of
vertical tubes, and removing the water as vapor
For spray drying, milk is concentrated to 40-50%
11. Homogenization
It is not mandatory.
During homogenization free fat is transformed into globules due to protein
adsorption.
Pressure is 5-15 MPa
Homogenization of highly concentrated milk (more than 3:1) destabilizes protein
and decreases powder solubility.
12. Heating
Before entering the drying chamber
Concentrated milk feed is slightly heated
To reduce its viscosity
To increase the energy available for drying
13. Air Filtration
Air filter is used to prevent contamination due to dust or any other particulate
matter
14. Feed Pump
Three piston pump with pressures upto 300-400 bar is used for pumping feed
15. Atomization
Atomization of the concentrated milk is the principle of the spray drying process
The atomizer may be either
A pressure nozzle or
A centrifugal disc
16. CONTINUE...
By atomization the concentrate is converted into droplets of size10-200 um, with
the greatest portion in the range 40-80um
The concentrate is converted into droplets of size10-200 um
With the greatest portion in the range 40-80um
17. Drying Chamber
Concentrated milk feed comes in contact with hot air here and is dried
Co-current flow of hot air is preferred
By controlling the size of the droplets,
The air temperature
And the airflow
It is possible to evaporate almost all the moisture while exposing the solids to
relatively low temperatures
External hammers are used on the cone to avoid buildup of dried particles
18. Cyclone Separator
The principle of cyclone separation is based on the centrifugal force exerted on
a particle
It separates particles based on their density. Fines are sent forward to the filters.
19. PACKAGING AND STORAGE
Milk powders are immensely more stable than fresh milk but protection from
moisture
Milk powder is packed into either plastic-lined multi-wall bags