The entire volume of media is sterilized at once through the use of thermal or radiation techniques.
Heating requires the addition of energy throughout the entire medium volume.
This can be done by adding heat through a jacket on the vessel. The temperature is increased until it reaches the sterilization temperature where it is held for a set period of time. During this phase, most of the unwanted microorganisms are destroyed. Finally, the system is cooled to bring the sterile media back to the desired temperature. For radiation sterilization, the process is similar to above, although it uses radiation intensity instead of heat.