Autoclaves for Microbiology: Types, Use Cases & More

Whether it’s culturing clinical samples or confirming pathogen identity, microbiology laboratories are responsible for doing the important work of understanding the microorganisms that impact human health. And when you’re working with such sensitive materials, there can be no room for error, especially when sterilizing instruments. That’s why an autoclave is an essential piece of equipment in any microbiology lab. Choosing the right unit, though, is sometimes easier said than done.

In this blog post, we’ll help you understand what an autoclave is, how it works, why it’s so important for microbiology, and how to make an informed purchasing decision for your lab.

What Is an Autoclave?

An autoclave, also known as a steam sterilizer, is a sealed, pressure-rated chamber used to sterilize lab materials and instruments by exposing them to saturated steam under pressure for a set time and temperature. By putting goods (also known as loads) in direct contact with pressurized steam, autoclaves reliably inactivate microorganisms, including hardier forms such as spores. Pressure enables steam to reach higher temperatures than boiling water, which kills microorganisms. This combination of steam, heat, pressure, and time makes autoclaving the most dependable method of sterilization in microbiology labs and other healthcare settings.

The concept of using a closed vessel to raise the boiling point of water dates back centuries. Denis Papin’s 1679 steam digester, an early pressure cooker, is often cited as a forerunner to later pressurized-steam devices. The invention of the modern autoclave, though, is credited to Charles Chamberland, who designed what became known as the Chamberland autoclave in 1879 as part of his work on sterilization in bacteriology at the Pasteur Institute.

How Do Autoclaves Work?

Autoclaves work by putting items into direct contact with saturated steam inside a sealed pressure vessel for a specified time and temperature. When hot steam touches a cooler surface, it condenses into water; this phase change quickly dumps a large amount of heat into the goods being sterilized. That rapid heat transfer is what makes autoclaving one of the most effective sterilization methods, especially when compared to dry heat. The pressure in the autoclave mainly matters because it enables steam to reach temperatures higher than 100°C (212°F) without boiling away.

During steam sterilization, air is removed from the chamber either using a vacuum pump or a process known as gravity displacement. Air pockets act as insulation, lowering heat transfer and creating cold spots where microbes can survive, so this step of the autoclaving process is essential.

Here’s an example of what a basic autoclave cycle looks like:

1. Air is purged from the chamber, and the chamber is heated so steam can penetrate the load. Most autoclaves use one of the following methods for air removal:
   • Gravity displacement: Steam enters and pushes any air in the chamber out through a drain.
   • Pre-vacuum: The autoclave uses one or more vacuum pressure pulses to evacuate air from the chamber, then injects steam, repeating the process as needed to remove air from porous loads.
2. Once the chamber reaches target conditions, the autoclave holds the load for a programmed time. Cycles are validated as a combination of temperature and time, and the correct amount of time varies by load depending on what you’re sterilizing and how it’s packed. For example, a tray of unwrapped metal tools will require different parameters than a densely packed bag of waste or bottle of liquid media.
3. The autoclave carefully releases the chamber pressure. Again, conditions vary based on load type. Liquids usually require a slow, controlled exhaust to prevent boil-over and broken containers, while dry goods tolerate faster heat exhaustion. Waste loads also have their own considerations, since trapped and dense packing can create cold spots.
4. The final stage, drying and cooling, is critical for wrapped or porous loads, as a wet wrap can wick contaminants back onto an instrument after sterilization. Many pre-vacuum autoclaves use a post-sterilization vacuum plus heat to remove moisture. Liquid loads usually bypass drying and instead cool under controlled conditions.

The success or failure of this process depends on a few variables:

• Steam must contact every surface of the load. Microbiology labs should avoid placing tightly sealed containers (which can also explode when autoclaved), overstuffed bags, and nested trays in the autoclave chamber and should evenly distribute goods to ensure even steam penetration.
• Liquid loads behave differently than dry goods, and liquid sterilization is limited by heat-up and cool-down time. For example, the contents of a large bottle containing liquid media may lag behind the chamber temperature, so liquid cycles compensate with longer holds and slow exhausts. Microbiology labs should use vented caps and secondary containment and provide proper headspace when sterilizing liquid loads.
• Porous and wrapped loads trap air, which can impede proper sterilization. Microbiology facilities should use pre-vacuum cycles for liquid loads and pay close attention to air removal tests.

Common Types of Autoclaves

There are many different types of autoclaves used for microbiology labs, which break down into three categories: class, function, and capacity. Let’s take a closer look at each category.

Class
Autoclaves are classified by the air removal method they use and the type of goods they’re designed to sterilize.

• • Class B autoclaves use a water ejector (with optional booster pump) or liquid ring vacuum pump to remove air from the chamber and are suited for porous materials, hollow instruments, and dry goods (wrapped or unwrapped).
  • Class N autoclaves use gravity displacement to remove air from the chamber and are best suited for unwrapped solid instruments.
  • Class S autoclaves incorporate features from both Class B and Class N autoclaves.

Function
What function an autoclave serves depends largely on its design.

• • Hinged autoclaves feature a single door with a radial-arm hinge for easy opening and closing, which makes them ideal for applications which require frequent access to the chamber.
  • Horizontal autoclaves have a horizontally oriented front-loading chamber, which makes them easy to load and unload with trays, racks, and other items. Large units can support high-capacity sterilization and sterilization of larger equipment, such as rolling carts and carriages.
  • Pass-through autoclaves are specifically designed for environments that require strict control over sterilization zones, with doors on either side of the chamber.
  • Tower autoclaves feature two vertically stacked front-loading chambers, making them an excellent option for any microbiology lab that requires additional sterilization capacity but has limited space to work with.
  • Vertical autoclaves have smaller, vertically oriented chambers, which open at the top.

Capacity
For this category, capacity refers to both the size of the autoclave chamber and its overall physical footprint.

• • Small capacity autoclaves, which include benchtop, tabletop, and floor models, are used for low-throughput sterilization and laboratories with physical constraints. Most small capacity autoclaves have a chamber volume ranging from 1 to 45 liters and can handle smaller instruments and glassware.
  • Medium capacity autoclaves are suitable for a wide range of applications and facilities with moderate sterilization needs, with chamber capacities ranging from 45 to 200 liters.
  • Large capacity autoclaves, also known as industrial autoclaves, have chambers exceeding 200 liters and are designed for high-volume, large-scale sterilization. These autoclaves are used almost exclusively for larger items, such as trays, bedpans, racks, and carts.

What Materials Can You Autoclave in a Microbiology Lab?

Autoclaves are one of the most versatile pieces of equipment in any microbiology laboratory, but they aren’t universal. Always refer to the manufacturer’s instructions for use (IFUs) prior to autoclaving any instrument.

Here are some common microbiology loads you can autoclave, and tips on how to ensure best results:

GlasswareFlasks, bottles, test tubes, graduated cylinders, pipettes, petri dishesGravity (unwrapped, empty), pre-vacuum (wrapped)

• • Rinse debris off of goods before loading the autoclave chamber
  • Arrange goods so steam can evenly penetrate the load, with openings up or at an angle and unsealed
  • For bottles and tubes, keep closures loose or use vented covers
  • Let sterilized items cool before opening the chamber, as rapid pressure release can stress hot glass

Items that should, under no circumstances, be placed in an autoclave include:

• Volatile, flammable, or corrosive chemicals and solvents
• Bleach, formalin, and many disinfectants
• Radioactive materials
• Sealed containers or pressurized vessels
• Heat-sensitive plastics and electronics

8 Use Cases for Autoclaves in Microbiology Labs

Autoclaves show up frequently in microbiology workflows because they solve two problems at once: they help labs create sterile inputs for experiments and safely neutralize biological hazards. Common use cases for autoclaves in microbiology labs include:

1. Establishing a sterile baseline for experiments: Many microbiology workflows only work if you can trust the starting conditions. Autoclaves are one of the most effective ways to  create a neutral starting point for setup so growth, inhibition, or detection can be attributed to the experiment, rather than stray contamination. By routinely sterilizing inputs and labware, you can protect the interpretability of results over weeks of work.
2. Enabling fast, repeatable turnaround: Microbiology is full of repeated cycles: a new batch, a new set of cultures, a new run of assays. Autoclaving supports this cadence by making sterilization a predictable step you can schedule and standardize.
3. Containing risk at the point of generation: Preventing viable organisms from leaving the bench area as routine trash is critical to biosafety. Autoclaves help labs neutralize at the source, so downstream handling is safer for everyone, including colleagues who never directly interact with cultures. In higher consequence settings, autoclaves also keep risk inside a controlled boundary or reduce reliance on perfect handling during transport or disposal.
4. Closing out work safely at the end of a run: Once you’re done culturing, enriching, or amplifying organisms, you need a reliable way to shut the process down so it doesn’t persist in the environment or accidentally spread across projects. Steam sterilization can be used for routine end-of-day cleanup, end-of-week disposals, and in project hygiene for long-running studies.
5. Preventing cross-contamination: With multiple organisms and experiments running in parallel, cross-contamination is a constant risk. Autoclaves support clean boundaries between strains, experimental conditions, and groups that share equipment, so yesterday’s work doesn’t bleed into today’s.
6. Supporting controlled material flow: In some environments, an autoclave is part of the building’s contamination-control design. Pass-through units and sterilization rooms help enforce directional movement of materials, so clean items don’t travel through dirty corridors, and vice versa.
7. Building a defensible sterility and decontamination program: In regulated or quality-driven labs, it isn’t enough to sterilize — you need to show that you sterilized under controlled, repeatable conditions. Steam sterilizers support this by producing consistent cycle records and enabling a monitoring routine that can stand up to audits and internal reviews. Even in non-regulated labs, that same structure can help troubleshoot contamination events by removing uncertainty from the conversation.
8. Resetting labs after contamination events or process changes: When contamination shows up unexpectedly, labs need a practical way to re-establish trust in their environment and materials. Autoclaves support remediation by rapidly sterilizing reusable pieces of the workflow while you investigate what went wrong. They’re also valuable for reestablishing a baseline when moving spaces, onboarding new staff, or adopting new organisms.

13 Questions to Ask Before Buying an Autoclave for Your Microbiology Lab

Before you start comparing models and chamber sizes, it helps to step back and define what the “right” autoclave actually means for your microbiology lab. The questions below are designed to raise real requirements early, so you can evaluate options based on how your lab actually operates.

• What are our primary use cases, and what do we autoclave most often?

Make a short list of your top three to five loads. The “best” unit for media-heavy labs can be the wrong unit for waste-heavy facilities, and vice versa, so it’s important to be specific about your needs.

• What biosafety context are we operating in?

Your biosafety level can affect requirements such as pass-through configurations, effluent handling expectations, door interlocks, or how you document waste cycles.

• What cycle types do we need available on day one?

Confirm that any unit you’re considering supports the cycle types your lab will regularly rely on, and whether any advanced cycles are optional add-ons or included as standard.

• Do we need pre-vacuum performance and, if so, for what loads?

If you frequently sterilize wrapped, porous, or hard-to-penetrate loads, dynamic air removal performance — and how the autoclave verifies that performance over time — is a critical consideration.

• How much throughput do we need at peak?

Think in terms of bottlenecks: how many liters of media per week, how many waste bags per day, how many users, and so on. Many labs buy units with enough capacity for normal weeks, only to lack the throughput they need during peak periods.

• What chamber size is right for us?

Volume alone is misleading. Ask what you can fit in a single run: the tallest bottles you use, the widest trays, your waste bag holder, or a full cart. Bring examples of dimensions and test-fit with racks and baskets for an exact fit. Beyond capacity demands, think about the size of your facility and how much space you can realistically use to accommodate a steam sterilizer. If your lab is small and space is at a premium, but you still require high throughput, it may be worth exploring a tower unit, which offers two chambers with a conservative footprint.

• Is a front-loading or top-loading unit the best option for our team?

This is about workflow and injury risk as much as preference. Consider who will load the autoclave, how heavy the loads are, whether they’ll be handling hot liquids, and whether they can use carts and shelves comfortably.

• What installation constraints are we up against?

Footprint, door swing, required clearances, floor loading, ventilation and heat rejection, and whether the route into the lab (doors, elevators, hallways) can physically accommodate the unit will all impact what options are available to you.

• What utilities will the unit require, and what do we already have?

Check electrical specs, water quality expectations, drain requirements, steam source, and whether you need water softening or filtration. Utility mismatches can drive up the total cost of ownership, so it’s better to get this out of the way before you buy.

• What does validation look like for our environment?

If you need installation qualification, operational qualification, performance qualification, or periodic requalification, clarify what documentation the manufacturer provides, what third-party services are available, and what your internal responsibilities are.

• What is the true cost of ownership over five to 10 years?

Beyond purchase price, factor in installation, utilities, consumables, validation, service contracts, downtime, and parts to make an informed purchasing decision.

• Who will service the unit, how fast, and with what guarantees?

An autoclave is only good if it works properly. In addition to information about local technician coverage, typical response times, parts availability, warranty terms, loaners, and whether service can be scheduled around your lab’s peak periods, the right manufacturer should outline any preventative maintenance measures your staff can take to keep equipment running between repairs.

• What is our growth plan, and do we need redundancy?

If more users, more waste, or more media is likely within a year or two, plan for capacity now. It may be that the right answer isn’t a bigger autoclave, but rather a second unit or shared facility access to avoid a single point of failure.

What Is the Best Autoclave for a Microbiology Lab?

The best autoclave for a microbiology lab is the one with the capacity and capabilities to meet your facility’s unique needs.

Here at D.A.I. Scientific, we supply a wide range of sterilizers, from benchtop autoclaves to large capacity units, from some of the most respected laboratory equipment manufacturers in the world. Whether you need help identifying the right model for your laboratory or want to request a quote for a specific unit, our knowledgeable and friendly team is here to assist you