Autoclave Sterilization or What is Autoclaving?

Autoclave definition

  • An Autoclave is a pressurized device designed to heat aqueous solutions above their boiling point by increasing pressure above normal atmospheric pressure to achieve sterilization.

What is an Autoclave?

  • Steam sterilization, also known as autoclave sterilization, is a moist heat sterilizing procedure that is widely used in hospitals, businesses, and labs to clean glassware, equipment, and various samples.
  • It is one of the varieties of steam sterilizers that removes pollutants from the goods in a manner similar to a conventional pressure cooker by using high-pressure steam to kill bacterial cells and fungal spores.
  • In this section, we’ll go through the standards for ensuring that products stay sterile as they pass through several sterilization cycles.

Autoclave Meaning

  • An autoclave is a sterilizing device that leaves equipment and supplies contaminant-free by holding pressure saturated steam at a set temperature for a predetermined amount of time.
  • The size of the loads and contents can affect the steam temperature and pressure.
  • A physical approach of moist heat sterilization offers a wide range of applications and is the most reliable method among chemical, radiation, and gas sterilization techniques in Pharmaceuticals.
  • It is a physical method of sterilization and disinfection that eliminates harmful microorganisms on the loads inside a pressure vessel, including bacteria, viruses, fungi, etc.


Numerous scientists have made contributions to the development of autoclave technology, which we will address below:

  • 1681: Denis Papin initial designed the pressure cooker that works fairly similar to an autoclave. He called this apparatus a “Steam digester”.
  • 1879: Charles Chamberland (French microbiologist) re-invented and invented a mechanism called an “Autoclave”.
  • Sterilization of surgical tools, lab equipment, pharmaceutical goods, and other materials is accomplished using an autoclave.
  • It has the ability to sterilize hollow objects, liquids, solids, and devices of all sizes and shapes.
  • The size, design, and functioning of autoclaves varies.
  • Both a pressure cooker and a very simple autoclave employ the power of steam to kill bacteria, spores, and germs that are resistant to boiling water and powerful detergents.
Autoclave Diagramme

Related: Autoclave Diagram and basic component

Autoclave Principle

  • Depending on the type of material being autoclaved, a specific amount of time and temperature must be used for sterilization.
  • The sterilizing agent in autoclaves is pressured steam. It is based on the idea of moist heat sterilization, in which products are uncovered to direct steam for a set period of time while being subjected to temperature and pressure controls.
  • Therefore, the steam’s quality, pressure, temperature (°C), and time are all factors in autoclaving.
  • The four key factors needed for an autoclave to successfully sterilize an object are time, steam, temperature, and pressure.
  • The autoclave uses moist heat to absolutely denaturize and kill all microbial cells, intracellular structures, and spores.
  • Enzymes and structural proteins coagulate in moist heat.
  • Depending on the type of material being autoclaved, different temperatures and times are needed for sterilization.
  • Using higher temperatures for sterilization requires shorter times. The most frequently employed temperatures are 121°C and 132°C.
  • In order for steam to reach this high temp., steam has to be driven into the chamber at a pressure higher than normal atmospheric pressure (atm). 

Related: Autoclave Basic Components, Leak Test used in Autoclave , Autoclave Types, biological indicator for autoclave

Important Parameters of an Autoclave

  • The following factors affect how an autoclave operates and needs to be maintained:

Autoclave Temperature and Pressure

  • To achieve strong microbicidal action, autoclaves use dry saturated steam at high pressure and temperatures. Regular temperatures in a gravity displacement autoclave and pre-vacuum sterilizers are 121°C (250°F) and 132°C (270°F), respectively, at standard pressures of 15 and 27 p.s.i (Pound per square inch).
  • Pressure is determined in pounds per square inch, or p.s.i unit. If the pressure within an autoclave is raised above atmospheric pressure, the boiling point of the water inside the pressure vessel will also rise. (Generally, in normal conditions boiling point of water is 100°C.).
  • Water will become steam when the boiling temperature rises due to one of its characteristics, the latent heat of evaporation (heat necessary to turn water into steam or vapours).
  • As a result, the penetration of steam into the autoclave’s contents increases. The killing power of microorganisms is also improved by the latent heat of evaporation.


  • Quality steam is vital for effective sterilization. The vapor must hold a portion of 97% steam (vapour) & 3% moisture (liquid water). The steam and moisture ratio is essential for effective heat transfer.
  • For effective heat transfer, the portion of steam and moisture must be more than 3%. A fraction < 3% is considered as a “superheated” or “Dry steam”, which is considered ineffective for steam sterilization.
  • Therefore, it is believed that the most efficient sterilizing agent for cleaning glassware, culture media, surgical dressings, etc. is wet heat or heat saturated vapour.


  • The minimum amount of time needed to sterilize the contents in the pre-vacuum and gravity displacement autoclaves is 4 minutes, and 30 minutes, respectively.
  • The kind and load of the items inside an inner chamber may affect the sterilization time. The sterilizing time may be extended by the weight of the glassware, huge liquid volumes, and dense solids.
  • The use, is advised; higher sterilization temperatures and shorter sterilization times are preferred to a combination of lower sterilization temperatures and longer sterilization times.

Related: Advantages/ Disadvantages of an Autoclave, CIP and SIP in Pharmaceuticals, Bowie Dick Test, Positive control and negative control in Microbiology

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