The invention relates to a method of extending the production time of a pasteuriser. The pasteuriser is of the type which includes a plate heat exchanger with a number of sections, of which at least one section consists of regenerative section. The method comprises raising the temperature in the downstream part of the regenerative section to a temperature above 50° C., during a certain predetermined period of time and at regular intervals. During normal production, a part quantity of the product which passes downstream of the regenerative section is shunted past the regenerative section. At the regular intervals and during the predetermined period of time, a part quantity of the product which passes upstream of the regenerative section is shunted past the regenerative section. At the same time, all product passes the downstream part of the regenerative section during the predetermined period of time.