Systems and methods for adjusting the pressure in a cooking chamber of a pressure fryer. The pressure inside the cooking chamber is determined in response to detecting closure of a valve that vents the cooking chamber. The pressure in the chamber is compared to a predetermined pressure. If the pressure in the chamber is less than the predetermined pressure, a pressure assist system is activated. The pressure assist system includes an air pump and/or pressure source, and when activated, supplies a gas to the cooking chamber to increase the pressure in the cooking chamber. The pressure may be determined at a predetermined time after closure of the valve, and an amount of gas to be added to the cooking chamber determined based on a difference between the measured pressure and the predetermined pressure. Use of the pressure assist system allows for optimal cooking of batches of food of many sizes.