Beyond Temperature and Pressure: How Steam Quality Defines Sterilization Success

By Sylvan Poeckh

In pharmaceutical and biotechnology manufacturing, clean steam is an essential utility for achieving sterility. As it flows through autoclaves and production equipment, clean steam transfers moist heat energy via condensation onto contacted surfaces during a timed exposure, coagulating and denaturing enzymes and proteins to achieve sterilization. The effectiveness of this process can vary even with optimal temperature and pressure conditions. There are three physical properties in clean steam that can impact its sterilization capability: dryness, superheat, and non-condensable gases.

Steam quality testing verifies that these 3 physical properties meet requirements to provide optimal lethality during exposure.  Steam quality testing therefore serves as a crucial safeguard in pharmaceutical biotechnology processes, ensuring that your clean steam is meeting performance standards outlined in EN 285 and ISO 17665.  (While EN 285 is a European Standard, is it widely considered a baseline standard that is applied in the US and elsewhere.)  

Want to know more?  These 3 facts about clean steam may surprise you.

1. Clean steam can be “dry” or “wet”.  Wetness in steam refers to water that is in liquid phase. The presence of liquid reduces sterilization effectiveness due to the water carrying less energy. As mentioned earlier, condensation is an essential mechanism for steam sterilization. Excess water can also cause wet loads in autoclaves which can compromise sterility. Dryness should be ≥ 0.95 (or less than 5% liquid present) per EN 285. 

2. Clean steam can be “too hot”. Superheat refers to steam that at a given pressure is exceeding the temperature that would allow for condensation onto exposed surfaces. If the steam is superheated and therefore does not condense during exposure, sterilization capability can be negatively impacted. Superheat should not exceed 25°C per EN 285.       

3. Clean steam needs to be made of water vapor and not other “stuff”. That might sound obvious, but some quantity of other gases like air (O₂, CO₂, N₂) will always exist in clean steam as they are present as dissolved gases in the water supply that feeds the steam generator. Non-condensable gases like CO₂ will stay in gas phase during exposure which can negatively impact sterilization capability. Non-condensable gases should not exceed 3.5%, or 3.5mL per 100mL of condensate per EN 285.

Interested in learning more about Steam Quality Testing or Alcami’s other CQV services?

Download our Whitepaper: https://www.alcami.com/library/best-practices-in-steam-quality-testing/

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