TECHNOLOGY
USDA Uses Gas Injector and Mixing Chamber with Spray Dryer
Spray Drying Adapted for High-Acid Whey USDA process turns out free flowing powder from cottage cheese whey, transforms waste product into useful raw material U.S. Department of Agriculture has found a way around the traditional problem of processing cottage cheese whey. Last week at the American Dairy Science Association meeting, held in Madison, Wis., Francis P. Hanrahan and Dr. Byron H. Webb of USDA's Dairy Products Laboratory, Eastern Utilization Research and Development Division, told how they have successfully spray dried this type of whey. Key to the process is a specially constructed gas injector and mixer. This combination injects gas into the whey on the pressure side of a conventional spray drying line. The problem of what to do with the whey has long troubled cottage cheese makers. The undried whey is perishable and can't be kept for long without deteriorating. Also, because of its high moisture content, it's expensive to ship the whey from cheese plants to food or animal feed producers. Even after concentrating under vacuum, not enough moisture is removed to make the shipping economical. As a result cottage cheese whey has been a waste by-product. 66
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As a waste product it presents problems also. Disposal of the waste is a difficult and often costly operation. The whey pollutes streams and rivers into which it is dumped. The practice is also prohibited in many areas, because of adverse effects on aquatic life. If the low-solids whey could be easily and economically dried, the powder could be handled, stored, and shipped to food manufacturers. For many years low-acid whey (for instance, that from Cheddar, Swiss, or Italian types of cheese, pH 6.3) has been successfully dried by conventional spray drying processes. However, Dr. Webb explains, cottage cheese whey, which has a high acidity (pH 4.0-4.8), is difficult to dry. When spray dried by the conventional method, water removal is difficult and the particles tend to agglomerate and form lumps. This results in an unsatisfactory product which hinders the process by clogging the dryer. Special Mixer. By introducing a gas into a specially constructed mixer before the concentrate reaches the dryer, Mr. Hanrahan and Dr. Webb have succeeded in making a free flow-
ing, easily dispersible powder with less than 2% moisture. Their process makes it attractive now to recover for sale the solids of cottage cheese whey as a powder. In the process, the whey, which contains up to 95% water, is first pasteurized, then concentrated to 40 to 50% solids in a conventional vacuum evaporator. The concentrate is then pumped under a pressure of about 1800 p.s.i.g. into the specially constructed mixing chamber. At the chamber, air is injected under a pressure of 2000 p.s.i.g. The air (or other gas used in the process) agitates the concentrate and forms a very fine dispersion. The particle size or bulk density of the particles can be controlled by varying hydraulic and gas pressures and nozzle size. The thoroughly dispersed mixture, which is a foam, is sprayed into the dryer. Because the foamed droplets have a relatively large surface exposed to the drying air, the moisture is removed easily. Also the temperature of the drying air is lower when the product is foamed than when no gas is injected into the system.
