Control means and method for controlling the characteristics of the operation of a food processing device by selective adjustment of temperature and vapor pressure including a chamber to hold food in process, a reservoir to hold water to be evaporated to the air in the chamber where a first heater is located in the reservoir to selectively provide heat of vaporization to the water to be evaporated, and second heater is supplied to heat air supplied to the chamber to increase the temperature of the air to a second temperature where the control means are provided to regulate time periods for which energy is supplied to the first and second heaters to control the humidity and temperature in the chamber.