Thermal sterilization uses the thermal lability of a microorganism to prevent its growth. At elevated temperatures, the probability of an organism surviving depends on the magnitude of temperature and the duration of exposure. The medium shall remain unharmed, unless it is thermally unstable. Thermal instability of media causes degradation of the desired product as well as the targeted organisms. The most common form of thermal sterilization is steam addition. Steam is an inexpensive and effective carrier of heat. Below is a high-resolution picture of bacteria in media.

Most common method for controlling microbial growth
Very effective in destroying unwanted microbes
Low cost

Probabilistic - not absolute sterilization
Can degrade thermally unstable media
Produced by Scott Ogoreuc and Greg DiLeo