A tunnel pasteuriser comprises forward movement means (2) for moving products (3) to be pasteurised forward on a forward movement path along which there is a heating zone (4), a heat treatment zone (5) and a cooling zone (6).
Each of said zones is divided into two or more sub-zones equipped with spraying means (10) for spraying a treatment liquid (11) onto the products (3) in transit in the sub-zone, and at least one tank (12) for collecting the liquid (11) that was sprayed on the products (3). In each heat treatment sub-zone (9) there are also means (20) for collecting the liquid (11) which wet the products (3) being treated. The collecting means (20) can be switched between a first operating condition in which they direct the liquid (11) collected towards the collection tank (12) of the relative heat treatment sub-zone (9), and a second operating condition in which they prevent the liquid (11) collected from reaching the tank (12) of the relative heat treatment sub-zone (9).