MILK POWDER MANUFACTURING PROCESS/ दुधाची पावडर निर्माण प्रक्रिया
MILK POWDER MANUFACTURING PROCESS:
Powdered
milk or dried milk is a manufactured dairy product made by dehydrating liquid
milk through several drying processes until it is a powder. One purpose of
drying milk is to preserve it; milk powder has a far longer shelf life than
liquid milk and does not need to be refrigerated.
SEPARATION / STANDARDIZATION
The conventional process
for the production of milk powders starts with taking the raw milk received at
the dairy factory and pasteurizing and separating it into skim milk and cream
using a centrifugal cream separator. If WMP is to be manufactured, a portion of
the cream is added back to the skim milk to produce a milk with a standardized
fat content (typically 26-30% fat in the powder). Surplus cream is used to make
butter or anhydrous milk fat.
PREHEATING
The next step in the
process is “preheating” during which the standardized milk is heated to
temperatures between 75 and 120 °C. The milk is held in this condition for a
specified time ranging from a few seconds up to several minutes
(pasteurization: 72 °C for 15 s). Preheating causes a controlled denaturation
of the whey proteins in the milk and it destroys bacteria, inactivates enzymes,
generates natural antioxidants and imparts heat stability. The exact
heating/holding regime depends on the type of product and its intended end-use.
High preheats in WMP are associated with improved shelf life but reduced
solubility. Preheating may be either indirect (via heat exchangers), or direct
(via steam injection or infusion into the product), or a mixture of the two.
Indirect heaters generally use waste heat from other parts of the process in
order to reduce energy costs.
EVAPORATION
In the evaporator, the
preheated milk is concentrated in stages or “effects” from around 9.0% total
solids content for skim milk and 13% for whole milk, up to 45-52% total solids.
This is achieved by boiling the milk under a vacuum at temperatures below 72°C
in a falling film on the inside of vertical tubes, and removing the water as
vapor. This vapor, which may be mechanically or thermally compressed, is then
used to heat the milk in the next effect of the evaporator which may be
operated at a lower pressure and temperature than the preceding effect. Modern
plants may have up to seven effects for maximum energy efficiency. More than
85% of the water in the milk may be removed in the evaporator. Evaporators are
extremely noisy because of the large quantity of water vapor traveling at very
high speeds inside the tubes.
SPRAY DRYING
Spray drying involves
atomizing the milk concentrate from the evaporator into fine droplets. This is
done inside a large drying chamber in a flow of hot air (up to 200 °C) using
either a spinning disk atomizer or a series of high pressure nozzles. The milk
droplets are cooled by evaporation and they never reach the temperature of the
air. The concentrate may be heated prior to atomization to reduce its viscosity
and to increase the energy available for drying. Much of the remaining water is
evaporated in the drying chamber, leaving a fine powder with around 6% moisture
content with a mean particle size typically of <0.1 mm diameter. Final or “secondary”
drying takes place in a fluid bed, or in a series of such beds, in which hot
air is blown through a layer of fluidized powder removing water to the point of
a moisture content between 2-4%.
PACKAGING AND STORAGE
Milk powders are immensely
more stable than fresh milk but protection from moisture, oxygen, light and
heat is needed in order to maintain their quality and shelf life. Milk powders
readily take up moisture from the air, leading to a rapid loss of quality and
caking or lumping. The fat in WMPs can react with oxygen in the air to give
off-flavors, especially at higher storage temperatures (> 30°C) such as
found in the lower latitudes of the Tropics. Milk powder is packed into either
plastic-lined multi-wall bags (25 kg) or bulk bins (600 kg).
Actual Manufacturing can be seen in the link:
https://youtu.be/NkKC5dwd698
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