Abstract: Sealed, deformable, air-containing packages or pouches are subject to heat sterilization in a sealable processing vessel. The shape and integrity of the sealed deformable packages is maintained through precise temperature and pressure control. The improved process includes a method for calculating the partial saturated volatile material vapor pressures during the "come-up", "processing", and "come-down" phases. The partial saturated volatile material vapor pressure used during the "come-up" and "processing" phases is calculated at the highest temperature of the contents of the package. The partial saturated volatile material vapor pressure used during the "come-down" phase is calculated at the lowest temperature of the package. The present invention discloses an improved process for controlling the pressure inside retort equipment when sterilizing food in deformable plastic packages with film-type lids and any volume of headspace.