Dried milk products instantizing

The first instant non-fat dry milk product was marketed in 1954 based on pioneering research by Peebles [6.4.1.1]. Since steam condensing on solids wets surfaces directly and uniformly and, at the same time, transfers heat very effectively, which helps to partially dissolve solids that are then acting as binders (discussion of Fig. 4.5, Chapter 4), steam is used directly [B.97] or added for improved results (Fig. 6.4-14). 

Nonfat dry milk is produced from skim milk by condensing it with conventional equipment followed by spray or drum drying. The drum-dried product is relatively insoluble and is used principally for animal feeds. Over 95% of nonfat dry milk in the United States is used for human foods (American Dry Milk Institute 1982) and is produced by spray drying. Most instant NDM is made by rewetting the conventionally spray-dried product, allowing the particles to agglomerate, and... 

Nonfat dry milk (NFDM), lowfat dry milk (LFDM), and dry whole milk (DWM) are produced and used as functional ingredients in dairy, bakery, confectionary, and other food applications. Instantized NFDM is made primarily for home and institutional beverage and miscellaneous product applications (Hall 1976 Hall and Hedrick 1966). 

SPRAY DRYING. A process used in the production of numerous chemical and food products. It is widely used in connection with the production of powdered milk and instant coffee preparations. The spray drying is unique among dryers in that it dries a finely divided droplet by direct contact with (lie drying medium (usually air) in an extremely short retention time (3 to 30 seconds). This short contact time results in minimum heat degradation of the dried product, a feature that led to the popularity of the spray dryer in the food and dairy industries during its early development. In the case of coffee extract, water in the feed will range from 50 to 70%. 

So far, in all examples the method for agglomeration was based on the use of low-density gas fluidized beds. As discussed in Chapter 5 and in much more detail in earlier publications [B.48, B.93, B.97], adhesion by coalescence of irregularly moving particles in low-density fluidized beds yields relatively small, structurally loose, and low-strength agglomerates, which (if reconstitution in liquids is desired) exhibit instant characteristics. In most cases these processes operate continuously, but batch operations for very sensitive materials (vitamins) are also possible. Fig. 6.4.1-16 shows as examples the photomicrographs of two typical products (dry milk and coffee extract). 

Furthermore, drying leads to stmctures usually differing from those of the initial humid product. This can be a disadvantage, but it can also offer a new benefit, as for example the porous structure of mashed potato flakes, crispy granulates for breakfast cereals, instant dry milk powder, and so on. The drying process can, therefore, also be considered as a controlled texturing operation, a source of innovative and easy-to-use products. 

Coffee whiteners are products that are available in liquid, but more often in dried instant form. They are used like coffee cream or condensed milk. A formulation typical of these products is shown in Table 10.28. In contrast to milk products, plant fats are used in the production of coffee whiteners. Caseinates are usually the protein conpo-nent. The most important process steps in the production are preemulsification of the constituents at temperatures of up to 90 °C, high-pressure homogenization (cf. 10.1.3.4), spray drying, and in-stantization (cf. 10.2.5). 

Instantized milk powder normally exhibits low bulk density but higher water dispersibility than conventionally spray-dried powder. However, the extra heat exposure from the agglomeration and redrying treatments causes additional Maillard reaction, whey protein denaturation, and related chemical and physicochemical reactions that tend to lower product quality. 

When the product coming out of the spray dryer is too fine it does not wet readily and so is harder to reconstitute. To make the product more readily soluble, it is agglomerated in a small fluidized or vibrated fluidized bed, as shown in Figure 23.23. This two-stage arrangement is used in the production of instant coffee, milk powder, cocoa, etc. An extension of this basic concept is the so-called spray-fluidizer, which dries the material in two stages. In the first stage (spray dryer). 

Two-stage spray dryer systems are sometimes called Spray-Fluidizers, since a fluid bed is installed at the cone of the spray dryer chamber. Alternatively, a vibrated fluid bed (VFB) is installed at the bottom of the drying chamber. It can produce instantly soluble products, such as instant coffee, milk, cocoa, etc., by agglomeration of the product. It is ideal to handle heat-sensitive products. 

In a two-stage process, the spray dryer is the first stage the material is dried up to 10% (in the case of milk) instead of up to the final 3%-5% moisture. The final moisture content is achieved in the second stage, which is usually a vibro-fluidized bed dryer. The second stage consists of two parts. In the first part, the powder is dried and in the second it is cooled. The product is agglomerated to achieve instantizing. 

The drum dryer is also extensively used to dry and gelatinize or cook starch slurries, such as potato, rice, - wheat, " maize, com," soybean-banana, and cowpea slurries to produce pregelatinized starch for instant foods. Nonstarch, low-sugar foods, such as tomato puree, milk, skim milk, whey, beef broth, yeast," coffee, and malt extract, have also been successfully dried on a drum dryer. Heat-sensitive products such as pharmaceuticals and vitamin-containing products can be dried in a vacuum drum dryer. 

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