What Is An Autoclave & How Does It Work?

What Is An Autoclave & How Does It Work?

An autoclave is an important part of any laboratory. First invented in 1879 by Charles Chamberland, the machine uses steam to cleanse and sterilize the contents. Microorganisms, or microbes, require food, moisture, and the right temperature to multiply and survive. If you cannot starve them or dry them out, heat is the only way to kill them. Heat breaks down the proteins in the microorganisms, in a process called denaturalization. In this post, we'll explore what an autoclave does, how the instrument generally operates, and which types of autoclaves are available for use in laboratories.

What Does an Autoclave Do?

An autoclave is a device that allows for disinfection using steam sterilization. The autoclave chamber behaves much like a pot of boiling water to poach an egg or a pressure cooker. Both use moist heat to coagulate the proteins, which kills the microorganisms.

Autoclaves are commonly used in laboratory setting and healthcare facilities to sterilize various supplies, surgical equipment, and even medical waste. In the chemical industries, autoclaves synthesize crystals, cure coatings, and vulcanize rubber.

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How Does an Autoclave Work?

Autoclaves use a combination of steam and high pressure to transfer heat from the machine to the items inside it. Over the years, they’ve undergone a number of iterations and technological improvements. There are still basic mechanical models available today, but it’s also possible to get a fully computerized machine.

A basic autoclave process looks something like this:

  1. Boil water to generate steam that enters the chamber. As the steam comes in, the air is removed, and as the steam expands, it continues to be pushed out. Air is removed using either a vacuum pump or vacuum system seen in larger autoclaves, or by displacement, which is an option seen in smaller tabletop models.
  2. After all the air is removed, close the chamber’s exhaust valve to increase pressure and temperature. Continue to add steam to the chamber. Higher temperature and atmospheric pressure levels are required to perform sterilization. The recommended sterilization temperature ranges from 121°C (250 °F) to 135°C  (273°F).
  3. The sterilization process begins. Alsot known as holding time or sterilization time, materials may be in this cycle anywhere from three to 20 minutes, depending on the contents and size of the load.
  4. Open the exhaust valve and release steam to reduce pressure. This helps to cool the load.
  5. Finally, cool down the load so that it is safe to touch upon opening the autoclave.

Ultimately, the sterilization cycle length varies depending on what materials are being autoclaved, and how many of them there are in the load.

Types of Autoclaves for Lab Use


This is known as gravity displacement autoclaving. It is the most basic form of autoclave sterilization and is suitable for most laboratory equipment and supplies. This type of autoclave is useful because it’s simple and doesn’t depend on additional peripheral mechanisms to displace the air with steam. This lack of dependency also helps keep the costs low. Gravity autoclaves are the most common type available on the market and are recommended for most uses.

These autoclaves are best for non-porous items, that is, anything with a hard surface, including:

  • Biohazard waste
  • Most metals – stainless steel lab utensils and surgical instruments
  • Unwrapped goods
  • Type I borosilicate glassware

Gravity autoclaves are available in front-loading and top-loading configurations. Top-loading units provide maximum loading space, yet minimal floor space. You do not need any building steam connection because the vertical chamber allows water to rest at the bottom, which turns to steam thanks to a heating element located at the bottom.

This type of autoclave is also useful in high altitude geographic areas and in places with high humidity because they constantly maintain the relationship between heat and pressure in the chamber and can accommodate changes in boiling point with adjustments to the exhaust valve.

Smaller benchtop autoclaves are available for dental offices and tattoo studios, but larger units are available for labs with plenty of counter space and limited floor space.


Also known as pre-vacuum autoclaving, this type of autoclaving is best for situations where air cannot easily be removed from the objects to be sterilized.

For example, sterilizing animal bedding and cages or wrapped surgical instruments cannot happen without all of the air being removed. The vacuum function ensures the ambient air is removed and allows high-temperature steam to access areas where ambient air would normally be. This approach can also be more efficient at sterilizing things with hard-to-reach areas.

The type of autoclave you choose depends mostly on the media you intend to sterilize regularly. In general, steam sterilization is effective, dependable, quick, and non-toxic. It provides an inexpensive method to heat and penetrate the chamber’s contents, including liquids that have been appropriately contained.

This method, however, only works with moisture-resistant goods and cannot be used to sterilize oils or powders.

These autoclaves are best for sterilizing porous or large items, including:

  • Wrapped items
  • Pipette tips and other high-density polyethylene products
  • Solutions stored in appropriate containers, such as tissue culture flasks
  • Animal cages and bedding

Leasing vs. Buying Autoclaves: What’s Smarter?

Depending on the size, type, and the number you need, you could easily spend $100,000 on autoclaves alone. When starting a lab, it’s not practical to spend large sums on something that represents only a small part of what your lab does.

Leasing the lab equipment through Excedr gives you the autoclaves your lab needs, without a sizable upfront investment. And, because there’s no need to worry about service contracts since maintenance and repairs are included in the equipment lease, you can save even more money and time compared to buying outright.

Contact us today to learn more about how our equipment leasing program can help you.