Autoclaving: a physical sterilization process with many advantages
Last updated: 02. March 2026
The term "autoclaving" is derived from the Latin word "autoclavis," which means "self-closing". It refers to a specific physical sterilization process. This process aims to establish a state of sterility for suitable materials, equipment, or products. A combination of steam, high temperatures, and increased pressure is used for this purpose.
The process usually takes place in a so-called autoclave. This is a special pressure-tight container whose function can be compared to that of a pressure cooker. After the procedure has been carried out correctly, microorganisms such as bacteria, fungi, spores, or viruses are reliably inactivated. The goal is a Sterility Assurance Level (SAL) of at least 10⁻⁶, which means that the theoretical probability of contamination is less than one in a million.
How does the autoclaving process work?
The autoclaving process consists of the following phases, which take place in succession:
Loading phase: First, it is necessary to load the autoclave with the objects to be sterilized. A suitable arrangement is important here to ensure that the steam can reach all surfaces.
Venting phase: This phase serves to completely remove air (condensate removal), as air pockets would hinder the transfer of heat and prevent the sterilization effect. This is done either by steam inflow or vacuum cycles.
Heating phase: In this phase, which includes the so-called rise time, the sterilization temperature is built up inside the chamber. This is followed by the equilibration time until the interior of the items to be sterilized has also reached the required temperature. Saturated steam is used for this.
Sterilization phase: Once the defined parameters regarding temperature and pressure have been reached, the actual sterilization begins. The process typically takes place in compliance with standard parameters – approximately 121 degrees Celsius over a holding time of 15 minutes at the appropriate overpressure.
Cooling phase: After the end of the specified sterilization time, controlled steam release and pressure reduction take place. During this, the sterilized material cools down. To remove remaining residual moisture, drying of the objects may also be required.
What advantages does autoclaving offer?
The autoclaving process combines a number of advantages. When all parameters are taken into account, the process is highly effective – even against resistant spores. At the same time, no additional sterilizing agent is required, with steam acting exclusively as a natural medium. Accordingly, there can be no exposure to chemical residues. In addition, the autoclaving process is suitable for numerous materials.
In which industries is the process used?
The autoclaving process is used today in numerous areas where sterility is crucial:
- Pharmaceutical industry: Sterilization of containers, equipment, and closures.
- Medical technology: Reprocessing of implants and surgical instruments.
- Food industry: Health-safe preservation of food.
- Laboratories: Killing of microorganisms on waste products or equipment.
- Biotechnology: Sterilization of bioreactors, culture media, and laboratory equipment.
What materials are autoclavable?
Materials that are suitable for sterilization in an autoclave are called autoclavable. Glass is usually autoclavable as long as it is borosilicate glass. The same applies to corrosion-resistant metals.
Furthermore, many elastomers and high-temperature-resistant plastics are autoclavable. While polypropylene (PP) is very suitable due to its higher melting point, the sterilization of polyethylene (PE) in an autoclave requires special material types (such as HDPE) or adapted process parameters, as standard LDPE often cannot withstand the high temperatures of 121 degrees Celsius. Materials such as polystyrene (PS) or polyvinyl chloride (PVC) cannot be sterilized in this way. Organic solvents or flammable materials are also unsuitable.
Distinction between autoclave and sterilizer
The terms autoclave and sterilizer are sometimes used synonymously, which is technically imprecise. Sterilizer is the generic term for devices used to kill microorganisms. Such systems can be gas sterilizers, hot-air sterilizers, or steam sterilizers – i.e., autoclaves. Thus, every autoclave is a sterilizer, but not every sterilizer is an autoclave.