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Steam Sterilization

Steam sterilization is achieved by exposing the items to be sterilized with saturated steam under pressure. Steam enhances the ability of heat to kill microorganisms by reducing the time and temperature required to denature or coagulate proteins in the microorganisms.



  • Steam sterilization is one of the widely used and dependable methods of sterilization. It is fast, inexpensive and applicable to wide range of products.
  • Sterilization is a process of removal of all the viable forms of organisms from a substance. This mostly is meant to eradicate any living microorganisms in drug formulations, food materials, cosmetics etc.
  • Presence of the microorganisms would act as contamination and possibly infect the person when those products are used. If not, microbes would also enhance the rate of degradation of the product.
  • So to prevent infections and also for longer life of the product, sterilization is essential.


The Steam Sterilization Process

The steam sterilization process has the clear benefits of being non-toxic and relatively simple to control. The main parameters are:
  • Air removal
  • Drying
  • Steam contact
  • Time
  • Temperature
  • Pressure
  • Moisture
Pressure and temperature measurements are the most crucial factors.

Steam sterilization
  • Steam sterilization is a type of moist heat method of sterilization done by using an instrument namely the autoclave.
  • It is a very powerful method of sterilization as it can destroy microbes of all sorts from every nook and corner of the package.

Principle of steam sterilization:
  • As the name indicates, saturated steam is used as a sterilizing agent. It is formed due to boiling of the water at a temperature of 100 degree centigrade. The steam is in vapor form and is entrapped inside the autoclave without a chance of escape. Further, pressure is applied to help in formation of steam at lower temperature and also enhance penetration power.
  • When the steam gets in touch with the material, it kills the organism by transferring the heat to the microbe.
  • When the heat touches the microbe, the proteins and enzymes in the cells get coagulated and denatured instantly. So the cell structure of the organisms gets destroyed leading to immediate death.
  • Also when the steam transfers the heat, it cools down and condenses to water. This creates a vacuum over the point of contact leading to further steam condensation at that point and more heat transfer.
  • Thus the rapid heat concentration on the microbes leads to their death without any possibility if escape.
  • The autoclave is maintained at said temperature for suitable period of time. If the temperature increases, the time decreases and vice-verse.
              At 121 degree Celsius for 30 minutes or
              At 132 degree for 4 min.

Biological indicators: The process is monitored by using biological indicators. A strip of spores of geobacillus thermophilus is used to check the validation of sterilization.

Factors regulating the process include
  • Saturated steam: The steam should be dry (>97%)
  • Pressure: This helps to attain the desired temperature faster.
  • Temperature:This provides the lethal potential to kill the microbes.
  • Time: The contact time decides the extent of sterilization. But it also varies as per other factors like temperature and pressure.

Pros of steam sterilization:
  • It is applicable to wide range of substance like cotton, surgical equipment, nutrient media, water, liquid formulation etc.
  • The time of sterilization is faster compared to filtration method and also hot air oven method.
  • Besides bacteria, even their spores (dormant forms) and toxins are destroyed.
  • The technique is less expensive as it relies on water and electricity for the process.
  • Large scale sterilization can be done at a time.
  • The technique is simple and easy to handle.

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