Expansion is caused by a sudden disequilibrium between the product and the atmosphere which causes rapid steam generation within the product. The water is vaporized before it has time to diffuse to the surface.
Oven-puffing cereals are almost always made from rice or corn, or mixtures of these two grains, because both inherently puff with appropriately moisture content and in the presence of high heat.
For crisp rice, puffing is done at very high temperature (to 343 °C) in rotary toasting ovens or more modern fluid bed dryers in which high-velocity air removes the stagnant surface air layer to accelerated heat penetration. Due to the bumping, which has compressed the grains, and the high temperature, the grains immediately puff to 5-6 times their original size.
The puffed grains are cooled, fortified with vitamins and minerals, of required and treated with antioxidants.
Oven puff cereals
