Machine and method for thermally treating liquid or semi-liquid food products

A method for pasteurizing liquid or semi-liquid food products in a machine, comprising the following steps:

• providing a machine comprising:
• a substantially cylindrical first container configured for thermal treatment of a liquid or semi-liquid base product;
• a second container connected to and configured for containing and feeding the liquid or semi-liquid base product to the first container;
• a first stirrer mounted inside the first container and configured for mixing the liquid or semi-liquid base product in the first container;
• a thermal system comprising a first exchanger thermally connected to a wall of the first container and configured to release heat to the first container;
• the first stirrer including:
• a first, inlet end and a second, outlet end and extending between the first, inlet end and the second, outlet end;
• a first portion disposed at the second, outlet end that is externally continuously helically shaped and arranged within the substantially cylindrical first container to form an enclosed first helicoidal chamber between the first portion and the substantially cylindrical first container such that, as the first stirrer rotates, the liquid or semi-liquid base product is made to advance through the first helicoidal chamber along a direction of extension of the first container between the first, inlet end and the second, outlet end;
• a second portion having at least one radial blade, the second portion being disposed at the first, inlet end;
• the first portion configured to push the liquid or semi-liquid base product along the direction of extension of the first container while the second portion is configured to stir the liquid or semi-liquid base product;
• a recirculation duct connected to the first container and configured to receive the liquid or semi-liquid base product from the second, outlet end and recirculate the liquid or semi-liquid base product back to the first, inlet end;
• a substantially cylindrical third container configured for thermal treatment of a liquid or semi-liquid base product;
• the thermal system further comprising a second exchanger thermally connected to a wall of the third container for the thermal treatment of the liquid or semi-liquid base product inside the third container;
• and
• a second stirrer mounted inside the third container and configured to mix the liquid or semi-liquid base product in the third container, the second stirrer having a portion being externally continuously helically shaped and arranged within the substantially cylindrical third container to form an enclosed second helicoidal chamber between the externally helically shaped portion and the substantially cylindrical third container, the second stirrer having a third, inlet end and a fourth, outlet end and extending between the third, inlet end and the fourth, outlet end, so that as the second stirrer rotates, the liquid or semi-liquid base product is made to advance through the second helicoidal chamber between the third, inlet end and the fourth, outlet end;
• wherein the second exchanger is configured to cool the liquid or semi-liquid base product inside the third container;
• wherein the second outlet end of the first container is connected to the third inlet end of the third container such that the liquid or semi-liquid base product that has been thermally treated in the first container exits the first container and is conveyed directly to the third container;
• wherein the second container is connected to the first container and to the third container;
• a valve assembly connected between the second container and the first container and between the second container and the third container and configured to provide selective fluid connection from the second container into the first container and from the second container into the third container;
• continuously feeding the liquid or semi-liquid base product from the second container to the first container;
• pasteurizing the liquid or semi-liquid base product through the steps of heating the wall of the first container to a temperature between 50° and 85° C. and simultaneously making the first stirrer rotate to cause the liquid or semi-liquid base product to advance continuously from the first, inlet end to the second, outlet end of the first stirrer.