Instantization process

The principal purpose of instantizing is to improve the rate and completeness of reconstitutability of dried milk. During the spray drying process, the aim is to produce particles with a big surface/mass ratio, i.e., small particles. The reconstitution of small particles of powder in water is, however, difficult and requires intensive mixing for their dispersion. One of the major objectives of new innovations in the area of spray and fluid bed drying is to produce instant powders by effecting agglomeration.Agglomeration means getting smaller particles to adhere to each other to form a powder consisting of bigger conglomerates/agglomerates, which are essential for improving certain reconstitutional properties of powders such as wettability, sinkability, dispersibility, although the net solubility does not improve. The agglomerates in the size range of 100-150 microns are recovered as final product.

The production of instantized whole milk powder was not successful until 1970s.The presence of free fat hindered the easy wetting of the powder particles. This problem was overcome and instant properties were achieved by treating the agglomerated powder with lecithin.

Major systems of instantization of milk powders are Peeble process, Cherry-Burrel process, Blow-Knox process and Niro agglomerator. Each varies in equipment and details. The general features in common are:Wetting of the surface of powder particles with steam, atomized water or a mixture of both.Agglomeration whereby the particles collide due to turbulence and adhere to each other forming clusters.Redrying with hot air Cooling and sizing to eliminate the very small particles and very large agglomerates.

i) Peebles process: The powder pneumatically enters the agglomeration chamber. The particles are wetted to 10-15% moisture in the turbulent air-stream zone and form agglomerates. These fall into the next zone or chamber which re-dries them by means of filtered air at 110-121oC. The product is cooled, sized with rollers, screened and packaged. The fine particles are returned to be recycled through the agglomeration process.

ii) Cherry-Burrel process: This process consists of delivering dried milk at a uniform rate by air, screw or vibrator to a horizontal tube. Wetting and agglomeration takes place in the most rapidly moving air-product mixture, which passes into the cyclone. During wetting, the moisture of milk powder increases to 6-8%. Air returns from the top of the cyclone to recycle and the clusters drop into a filtered hot-air stream at 132-149oC. The product, while moving into the second cyclone, is dried by this air. The air is exhausted from the top of the cyclone and the product clusters descend into a horizontal shaker through which cooling reduces the temperature from 71-82oC to 37-38oC. The sifter removes the fine particles. The clusters pass through sizing rolls and are sifted and packaged.

iii) Blow-Knox process: Dried milk is measured by a rotary-feed valve into a line and fed pneumatically into a small agglomerate tube. An alternative system uses a vibrating trough to control product entry into the agglomerating tube. Steam wets the particles to about 7% moisture as they fall between two jets. Ambient air entering through radial slots in the agglomerating tube maintains the turbulence necessary for the formation of aggregates. The agglomerated product drops onto a conveyer belt for conditioning and transport to deck-type vibrating re-driers. Dried agglomerates are screened after they pass between sizing rolls. Fine particles are reprocessed through the system.

iv) Niro/Anhydro agglomerator: It is an attachment fixed to the bottom of the vertical-type drying chamber. Milk is dried to about 9% moisture content in the drying chamber. A vibrator transports the product from the drier to the inlet of the Niro agglomerator that consists of three sections.In the first section, agglomeration takes place; in the second section, redrying with hot air; and in the third, the product is cooled to room temperature. Very fine mesh screens convey the product through the three sections. Air that passes up through the screens goes out carrying the fine particles from the top of the agglomerator. Fine particles are returned to the drying chamber.