​Autoclave: Principle, Types, and Precautions

6th Jul 2021

​Autoclave: Principle, Types, and Precautions


In your tissue culture lab, the maintenance of aseptic conditions is an absolute necessity. To have a proper lab, you should be aware of the several sterilization techniques used in labs, their purposes, and the machines used to perform the process. But, how do these devices or machines work? What types of them are available and what are the differences? And, how do they help you in your work? These are some questions that need to be addressed when you are about to decide if you want the equipment or not, or which equipment will be suitable for your fashion of work!

By keeping these questions in mind, we are going to create a series of articles on the equipment of the tissue culture lab and how they work. In this article, you are going to learn all about autoclaves, their workings, and their uses. So, let’s dig in!

Preference Center

What is an autoclave?

Autoclave, also known as steam sterilizer, is the most effective machine for the sterilization of lab equipment, water, or media. The machine uses steam under pressure to kill bacteria, viruses, and spores present in/on the equipment or culture media. It’s used in scientific labs, healthcare facilities, and industrial operations.

The first autoclave was invented by Charles Chamberland in 1879. But, the concept of disinfection and sterilization was introduced in 1881 by Robert Koch. Then in 1933, the modern autoclave, the first pressure steam sterilizer with control performance, was developed.

Image: The simplest autoclave (pressure cooker)

By: William Rafti of the William Rafti Institute, Attribution,


The autoclave works on the principle of moist heat sterilization. The high pressure inside the chamber increases the boiling point of water for the sterilization of equipment. The higher pressure also ensures the rapid penetration of heat into the deeper parts of equipment. The moisture present in the steam causes coagulation of proteins of microbes causing irreversible loss of their activity and functions.

Source: Consteril

Image: Working or principle of autoclaves.


All size of autoclaves work on a single principle, that involves three cyclic phases of sterilization that are given below:

  • Purge phase: Air present in the sealed chamber is displaced with steam that moves in through the sterilizer.
  • Exposure phase: In this phase, the exhaust valve is closed and the temperature and pressure inside the sealed chamber are increased to the desired set point. The temperature is maintained for the set duration of time.
  • Exhaust phase: The exhaust valve is opened, steam is removed, and the chamber is restored to normal temperature.

Components of Autoclave and their functions

1. Pressure chamber

The pressure chamber is the main body of the autoclave. It consists of an inner chamber and an outer jacket. Generally, the inner chamber is made of stainless steel/gunmetal and the outer chamber is made of the iron case.

The autoclave in the labs and hospital comes with a jacketed chamber that is filled with steam and designed to reduce the time and cycle of sterilization. These autoclaves can range from sizes anywhere from 100L to 3000L. So, you can buy the machine according to your requirements.

2. Lid/Door

The lid, disconnect the chamber from the outside atmosphere and seal it to create the desired temperature and pressure inside the autoclave. Its consists of three other parts: Pressure gauge, whistle, and safety valve.

The pressure gauge shows the pressure build-up inside the autoclave and assures the safety of the machine and working conditions. The whistle present in the autoclave is the same as that of the domestic pressure cooker. It controls the pressure inside the chamber by releasing a certain amount of vapor.

The other crucial part of the autoclave is the safety valve. It has a thin layer of rubber, which bursts itself to release the pressure inside the chamber if the autoclave fails to perform its operations. It ensures your safety from any kind of autoclave explosion.

3. Steam generator (if applicable)

A steam generator is present underneath the chamber. It has an electric heating system that heats water to generate steam inside the chamber. Always, ensure the right volume of water is available in the generator to run the process smoothly and avoid burning or heating of autoclave parts.

4. Vacuum generator (if applicable)

This removes air from the chamber as the presence of any air pockets in the chamber might support the growth of any organism and your equipment will not be sterilized.

5. Waste-water cooler

Autoclaves are equipped with a waste-water cooler that cools the effluent (air, steam, and condensate) before it enters the draining pipes. It avoids damage of draining pipes that can be caused by extremely heated water.

Image: A schematic diagram of autoclaves with their different labeled parts.

Source: Microbenotes

Types of Autoclave

Today, different types of autoclaves are present according to your needs. It includes:

  1. Pressure cooker type/ Laboratory bench autoclaves (N-type): It’s a domestic pressure cooker that is a perfect fit for tissue culture enthusiasts or hobbyists.
  2. Gravity displacement type autoclave: It’s the most common type of autoclave used in research laboratories. In this autoclave, steam displaces air in the chamber by gravity through a drain port.
  3. Positive pressure displacement type (B-type): This is an advanced autoclave, in which steam is generated in a separate steam generator, which is then passed into the autoclave for sterilization of equipment.
  4. Negative pressure displacement type (S-type): This is the most expensive type of autoclave. It comes with a vacuum generator and steam generator that works efficiently to achieve complete sterilization of equipment.

Be precautious while using Autoclaves

  • Do not sterilize waterproof or water-resistant materials like oil or powders.
  • Do not overcrowd the autoclave with the vessel and equipment. If possible sterilize your equipment in a shift-wise manner.
  • Only use autoclavable bags to autoclave packages wastes.
  • Use autoclavable bags to sterilize your equipment. Do not use aluminum foils.
  • Do not fill the autoclave chamber up to the lid.
  • Never attempt to open the autoclave while it’s operating.
  • Tightly close the lid to ensure the completely closed condition of the autoclave for proper sterilization.
  • Do not use regular plastics or trays in the autoclave.
  • Never autoclave flammable, reactive, corrosive, toxic, or radioactive materials, household bleach, or paraffin-embedded tissue.
  • Fill the water in the steam generator up to the volume where it touches the end of the vessel or chamber of the autoclave.

It’s short and crisp information that you should know about autoclaves. It’s always better to understand the use and principle of equipment you are working with for a better understanding of the science behind it. And, how it works. Further, if anything goes wrong, you know what it is!!

Happy culturing!!

Source: Giphy

Written by: Anjali Singh

Anjali is a scientific content writer at PlantCellTecnology. She has joined the company in 2020 with her technical knowledge of tissue culture, a background in Plant Biotechnology, and research skills. Apart from writing educational articles for our tissue culture enthusiasts, she also helps them with their queries on the tissue culture processes.

Before joining PCT, she has worked with various other biotech industries as a Scientific content writer and holds good experience in laboratory work and research.

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