Puffed cereals are whole grains, grain parts, or a grain dough that has been formed into a specific shape and then expanded by subjecting it to heat and pressure to produce a very light and airy grain product. The two types of process that are normally used for puffed cereals are gun puffing and extrusion.
Gun Puffing. Gun puffing consists of a chamber (gun) that is charged with a quantity of grain material. The chamber is subjected to high-pressure steam (100-250 psig) for 5—45 s. The pressure is then released very rapidly giving a sound reminiscent of a gun. The shot of grain is propelled into an expansion vessel. The change from the high-pressure steam to atmospheric conditions causes the grain piece to expand to about 3-10 times its original volume. The puff is then dried to a final moisture content of 1-3% (4,5).
Extrusion. Extrusion employs either a single- or twin-screw extruder. A single flour or a mixture of grain flours is fed into the extruder. These flours may have been preconditioned with water or steam before extrusion. Other ingredients may be added to the extruder such as water or sugar syrups. The design of the screw, barrel elements, and die of the extruder impart desired characteristics to the finished product. Heating or cooling is accomplished through mechanical energy from the screw (6) and through jacketing the extruder barrel. Pressures in the extruder range from 500 to 2500 psig and temperatures range from
250 to 400°F. As the material exists from the end of the extruder it expands to release steam from the product. The produce is then dried to 1-4% moisture.
Puffed cereals are often coated with a sugar solution that may be flavored and dried to give a presweetened cereal. This coating is normally done in a rotating drum or screw auger where the puffed cereal is fed at a controlled rate. Sugar syrup is sprayed onto the cereal in the desired amount. The coated cereal is dried to remove excess moisture.
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