DRIED MILK OR MILK POWDER

ROLLER DRIED MILK POWDER

Dried milk (Milk Powder) products play a significant role in conserving the milk solids since their biological value can be retained for a long period of time under relatively simple storage conditions. The roller dried powder finds special application in the manufacture of infant foods, confectionery, ice cream, milk sweets etc.

Milk is concentrated by means of condensation to about 20-25 per cent of total solids in a vacuum pan or evaporator and fed to continuously revolving drum drier, which are internally heated with steam. The film of the dried product is continuously scrapped off by a stationary knife or doctor blade, located opposite in the point of application of milk. The dried milk film thus obtained is ground, which is then sifted, packed and stored.

Method of Manufacture of dried milk

The milk is separated (in case of skim milk powder) or clarified and standardized (in case of whole milk powder).

The milk is fore-warmed to 95°C and re-condensed to 20% total solids. Homogenization of the condensed milk is done in case of manufacture of whole milk powder.

The roller drums are observed for its correct alignment with the knife, cleanliness of the surface of the rollers, pressure build up in the drum and working condition of the powder conveyors and exhaust fan.

The condensed milk in the feed line is taken in to the feed trough and the scraping blades are adjusted. The rate of milk flow is ensured to the determined level in the trough and the dried milk is scraped off from the surface of the drum uniformly.

The semi dried and charred powders obtained initially have to be discarded. The conveyors are adjusted properly to carry the powder.

When the milk flow is over, the conveyors are stopped and some hot water is run over the drums.

The knife is taken off from the surface of the drum and supply of steam to the drum is cut.

The rollers are stopped only when there is no steam pressure inside and the rollers are sufficiently cool.

The vapour exhaust fan is stopped.

SPRAY DRIED MILK POWDER

Spray drying is the most important method of drying milk and milk products. By spraying in to a stream of hot air, the droplets formed present an extremely large amount of surface area and get dried immediately due to rapid evaporation of moisture. Milk is preheated and concentrated to 40-45% percent total solids.

Hot air is filtered and directed in to the drying chamber. The concentrate is atomized to obtain small particles ranging from 10-100m in diameter. The air leaving the drying chamber enters a cyclone separator where the fine particles are collected. The dried products are cooled, sifted and packed in suitable packaging material.

Method of manufacture of spray dried milk powder

The milk is separated (in case of skim milk powder) or clarified and standardized (in case of whole milk powder).

The milk is fore-warmed to 95°C and re-condensed to 40% total solids. Homogenization of the condensed milk is done in case of manufacture of whole milk powder.

The spray drier is cleaned, pipelines are connected and general conditions of the valves and cyclone separators are checked.

The steam is let in to the air heating coils. The exhaust fan is switched on, keeping the main door partially open.

The blower is started and the main door is closed.

The temperature of the hot air is adjusted to 180°C and this temperature is maintained for ten minutes to ensure the sterility of the unit.

The atomizer is started and allowed to obtain the required speed.

Initially, 20 litres of water is used for spraying through the feed pump.

When the outlet air temperature reaches 100°C, the feed is changed to concentrate. The temperature of the inlet air entering the drying chamber usually ranges from 150-260°C and the outlet air exhausted from the drying chamber ranges from 100-105°C. the relative humidity of the drying chamber is quite low i.e. 3-4%.

The milk powder is collected in the powder silo.

When the flow of milk is over, the balance tank is flushed with about 20 litres of hot water (90°C) and the flow of milk to the dryer is reduced immediately.