Spray dryer, food industry

The most widely available yeast biomass is a by-product of the brewing industry, where the multiplication of yeast during brewing results in a surplus of ceUs. Eor every barrel (117 L) of beer brewed, 0.2—0.3 kg of yeast soHds may be recovered. In the U.S., a substantial fraction is recovered and made available about 40 x 10 kg of brewers yeast aimually. The yeast is recovered from beer by centrifuging and dried on roUer dmms or spray dryers and sold as animal feed or a pet-food supplement. It can be debittered by alkaline extraction to remove the bitter hop residues, and is then sold mainly by the health-food industry. It is available as tablets, powder, or flakes and is often fortified with additional vitamins. Distillers yeast caimot be readily separated from the fermented mash and the mixture is sold as an animal feed supplement. 

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%. 

The development of the process has been closely associated with the dairy industry. The use of spray drying in the dairy industry dates back to around 1800, but it was not until 1850 that it became possible to dry milk on industrial scale. Since then, this technology has been developed and expanded to cover a large food group which is now successfully spray dried. Over 20,000 spray dryers are estimated to be in use commercially, at present, to agro-chemical products, biotechnology products, fine and heavy chemicals, dairy products, foods, dyestuffs, mineral concentrates, and pharmaceuticals in evaporation capacities ranging from a few kg per hour to 50 tons/h (Mujumdar 2000). 

Most food-processing companies use spray dryers to produce powdered products. Spray drying has the ability to handle heat-sensitive foods with maximum retention of their nutritive content. The flexibility of spray-dryer design enables powders to be produced in the various forms required by consumer and industry. This includes agglomerated and nonagglomerated powders having precise particles size distribution, residual moisture content, and bulk density. As examples, spray drying of milk, tomato juice, tea extracts, and coffee is discussed. 

Figure 9.31 shows an example of a spray dryer very commonly used in food and pharmaceutical industries. The drying air is heated by steam. Because of the usually high cost... 

In the food industry, because the spray dryer is commonly available, economical, fast, and produces good-quality material [16], it becomes the most common means of encapsulation. The encapsulation process is simple and similar to the one-stage spray drying process. The coated material is called the active or core material, and the coating material is called the shell, wall material, carrier, or encapsulant [43]. The active material to be encapsulated, such as an oil or fia-vor in an oil base, is dispersed in a hydrocolloid carrier, e.g., gelatin, modified starch, dextrin or maltodextrin, or gum arabic. After the emulsifier is added, the mixture must be... 

Flash dryers can be used as a drying stage in more complex systons, for instance, as a predrying stage to a fluidized bed drya (batch or continuous) or fluidized bed coola, spray drya, drum dryer, etc. In the food industry, flash dryers are often used after spray drying to produce foods that have lower moisture content than normal like special milk or egg powders and potato granules [5]. 

Spray drying is a technique with many existing and potential applications in the food industry. In spray drying the incoming feed material is atomised to form a spray (Masters, 1991). Evaporation takes place as the droplets in the spray come into contact with warm air in the dryer. Moisture is lost from the surface and replaced by water migrating from the centre of the droplet. Eventually, a dry shell is formed around the droplet and the loss of moisture slows. The dried particle is then removed from the air stream. 

Figure 10.31 shows an example of a spray dryer very commonly used in food and pharmaceutical industries. The drying air is heated by steam. Because of the usually high cost of the final product, more complex separation equipment is justified or necessary. A spray drying system with the atomizer located in the middle of the drying chamber is shown in Figure 10.32. With two air inlets it is possible to control the spray characteristics very well. The secondary air entering the bottom of the chamber decreases the moisture content of the product.

There are many ways to microencapsulate active components, such as spray drying, film coating, coacervation, carrageenan entrapment, molecular encapsulation using P-cyclodextrin, double emulsions, liposomes, and microemulsions (Vilstrup, 2001). Of these, spray drying is currently the best technology available to the food industry to produce stable, cost-effective, microencapsulated ingredients or products. Spray dryers, first constmcted in 1878 (Hayashi, 1989), are now widely used in the dairy industry and, in a modified form, by infant formulae manufacturers. 

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