A machine for pasteurizing liquid or semi-liquid food products, including: a first container for the thermal treatment of a liquid or semi-liquid base product; a second container for feeding the liquid or semi-liquid base product, connected to the first, thermal treatment container, for feeding the liquid or semi-liquid base product; a stirrer for mixing the product in the first, processing container and mounted inside the first, thermal treatment container; a thermal system including an exchanger associated with the walls of the first, processing container and configured to release heat at the walls of the first, thermal treatment container, the machine wherein the stirrer is externally helically shaped and extends between a first, inlet end and a second, outlet end, so that as it rotates, the liquid or semi-liquid product is made to advance between the first, inlet end and the second, outlet end.