Oven-Puffed Cereals

Oven-puffed breakfast cereals constitute one of the most important categories. Undoubtedly, the most popular is expanded rice. These products have less expansion compared to products expanded with gun-puffing. The preferred rice is medium or short with intermediate amylose content (15%-20%). Waxy rice is not recommended, nor is milled rice with a high incidence of microfissures or stress cracks and fat content (>0.25%), because it expands less and yields low-quality products. Generally, the kernel expands 2 to 5 times its original volume. The traditional process for oven-puffed rice is depicted in Figure 11.3. The unit operations are practically... 

Nowadays, most breakfast cereals are made either by original traditional processes or by using alternative extrusion methods. Commercial flakes, shreds, and oven-puffed cereals could be alternatively manufactured via extrusion. There are two major types of extrusion processes cold and thermoplastic. Cold extrusion is almost exclusively applied for production of pasta products (Chapter 10), whereas thermoplastic extrusion is used for manufacturing breakfast cereals and snack foods (Chapter 12). Undoubtedly, the most popular and versatile extrusion process is thermoplastic, defined as the combination of heat and mechanical shear to enhance starch gelatinization and dextrinization, protein denaturation, and inactivation of microorganisms, enzymes, and antinutritional factors. The changes in the properties of the starch and proteins result in the formation of a plastic material that could be formed and/or restructured into desired configurations. 

Breakfast cereals are typically manufactured using direct expansion or by forming dense pellets. Direct-expanded products are usually flavored and packaged, whereas pellets are usually transformed into their final shape by flaking, oven puffing, or gun puffing. 

Reachons such as these usuahy take place in continuous reactors such as chip (memory or potato) processing lines, retorts, kilns, and conveyer belts in which the sohds pass through an oven with reactive gases such as air or perhaps in a fluidized sohd bed reactor as in the shot from guns puffed rice and other grain cereals or in a slurry reactor such as a vegetable oil or fat fryer. Some typical sohds reactors are sketched in Figure 9-2. 

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