A method and apparatus is provided for pasteurizing and inactivating a continuously flowing product without scorching the product. Microwave heating is used to gradually raise the temperature of the fluid (11) up to the pasteurization or inactivation temperature. Preferably, the fluid is preheated to a temperature within a few degrees of the pasteurization or inactivation temperature. Surface conductive heating and heat regeneration can be used for economically preheating the fluid.
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