A method of heat-treatment of a product in a sealed container of a packaging material is disclosed. The method comprises placing the container in a treatment environment having a pressure (P) and a temperature (T), the pressure and the temperature having a ratio (P/T), and adjusting the temperature and/or pressure in the treatment environment to decrease said ratio over a duration in a time period, wherein said time period starts at a time of cooking onset of the product and extends over a time of cooling onset at which time a temperature decrease is started, said time of cooking onset being preceded by a first time period of temperature ramping during which said temperature is increased. An apparatus for controlling heat-treatment of a product in a sealed container of a packaging material is also disclosed.