Steam Sterilization Cycles, Part 5: Low Temperature Cycle

Steam sterilizers play a pivotal role in your lab’s research capabilities and throughput. However, how can you safely and properly sterilize load types that are more temperature-sensitive than others? To help you avoid overheating a specific load type, thereby compromising it, we introduce the fifth article in CSS’ ongoing Steam Sterilization Cycles series: 

Low Temperature Cycles

By default, most laboratory steam sterilizers operate in the range of 250–275° F (121–134°C). However, some units can be configured to run cycles as low as 140°F to accommodate objects that are heat-sensitive and heat-coagulable. Units with the capacity to operate at lower temperatures are commonly and aptly referred to as Low Temperature or Isothermal sterilizers, and they can run cycles like:

• Low-Temperature
• Moist-Heat
• Inspissation
• Pasteurization
• Fractional Sterilization

However, of these, the most common cycle is the Low Temperature Cycle, which can be programmed to operate at temperatures between 158–212°F (70–100°C) with no chamber pressure. The basic premise of these Low Temperature units is that steam flows freely, at atmospheric pressure, evenly throughout the chamber. A basic laboratory autoclave that is not equipped as a Low Temperature unit will not evenly disperse the steam at a low temperature (temperatures below 212°F).

For those with a steam sterilizer capable of running the Low Temperature Cycle, here are answers to two of the most commonly asked questions about the Low Temperature Cycle:

When is it appropriate to use a Low Temperature Cycle?

A sterilizer operator may need to sterilize objects that are not heat-stable, prone to congeal, or shouldn’t reach temperatures higher than atmospheric steam. Examples include:

• Thermoplastics, like LDPE
• Sensitive liquids, like milk or baby formula
• Some medical devices
• Media and agar preparation, as this cycle allows for the media (agar) to melt without overheating it

As well, Low Temperature autoclaves can be used as a way to reduce (not eliminate) the total microbial burden of a given load.

How long does a Low Temperature Cycle take?

In theory, because these cycles operate at below the boiling point of water, cycle times should be longer than your typical steam sterilization cycle (at 250°F for 30minutes). Typical Low Temperature cycle times range from 45 to 90 minutes and will often be repeated for multiple days on the same load as not to denature or caramelize it.

As such, Low Temperature Cycles should be planned out thoughtfully and carefully, and, if applicable, be validated with biological indicators. In general, cycle times will vary depending on the size of your sterilizer, the size and type of load, the temperature at which the sterilizer is operating at, and how the load is packaged.

To get an overview of steam sterilization, check out our video here:

At CSS, it is our mission to help you get the most out of your steam sterilizers so you can properly sterilize your unique load types. So we encourage you to visit the Chamber Blog for more useful information; to catch up on this series (Part 1, Part 2, Part 3, Part 4); or to contact our team of sterilization experts to ask questions and learn more. And don’t forget to stay tuned for more articles in this ongoing series—we’ve got a lot to share!