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The presented paper reviews the existing literature dealing with rice puffing and optimum conditions of this process. The rice pre-treatment procedures and puffing conditions (dry heat, microwave, gun-puffing) are considered. The optimum composition of the raw material is also mentioned.

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The microwave power is a parameter greatly influencing the rate of heating. Several authors reported on certain differences between the rated power output as a parameter used by oven manufacturers in the labelling of ovens, and the power actually delivered to the heated product. A review of the respective information is given in this article together with the results of own experiments following the influence of the oven type and the heated substance parameters on the power actually absorbed in the substance volume during its heating. As the heated substance, water and solutions of NaCl and sucrose of different concentrations were used. For the heating, four types of domestic microwave ovens and glass and plastic containers, were used. The decreasing of the efficiency of heating with the decreasing volume of the heated substance and a certain relation between the rate of this decrease and the types of oven and of substance was estimated. With the small cavity ovens, a lower rate of the decrease of the absorbed microwave power with the decreasing volume of the substance was found as compared to the large cavity oven. A certain influence of other technical oven parameters is shown in the comparison of the tests results with the ovens of the same rated power and the cavity volume. In addition to the substance volume, also its dielectric properties probably influence the microwave power absorbed in small samples during the heating. No simple dependence can be seen on the basis of the tests results between the type of container used in the tests and the power absorbed in the heated substance.  

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