The invention relates to a method for preventing the formation of biofilms in pasteurisers and thereby extending the production time before a pasteuriser (1) has to be stopped for cleaning. Said pastueriser (1) is of the type which includes a plate heat exchanger having a number of sections, of which at least one section is a regenerative section. The method comprises the step of raising the temperature in the downstream part of the regenerative section (5) to a temperature above 50°C during a predetermined time at regular intervals. During normal production, part of the product which passes downstream of the regenerative section (5) is shunted past the regenerative section (5). During said intervals all product passes the downstream part of the regenerative section (5), while part of the product which passes upstream of the regenerative section (5) is shunted past the regnerative section (5).
