Media sterilization is carried out with
the autoclave, basically a huge steam
cooker. Steam enters into a jacket surrounding
the chamber. When the pressure from the
steam is at a certain point in the jacket, a valve
allows the steam to enter the chamber. The
pressure will go up over 15 pounds per square
inch (psi): at this point the timer begins to
count down--- usually for 15 minutes, depending
on the type of media. The high pressure in a
closed container allows the temperature to go
above the highest temperature one could get
by just boiling, around 121 degrees C.
Therefore, the parameters for sterilization with
an autoclave are 121 C at >15 psi for 15
minutes. Fifteen minutes is the thermal death time for most organisms (except some really
hardy sporeformers).