The invention provides methods and devices for heating or cooling viscous materials such as meal emulsions useful for producing food and other products. The devices include a heat exchanger comprising a first plate, a second plate attached to the first plate, and a first spacer and a second spacer arranged between the first plate and the second plate. The first plate, the second plate, the first spacer, and the second spacer define at least one temperature controlled passage for a product to pass through the heat exchanger.