Moist heat

Moist heat sterilization describes sterilization techniques that utilize hot air that is heavily laden with water vapor and where this moisture plays the most important role in the sterilization. Heating an article is one of the earliest forms of sterilization practiced. The various procedures used to perform moist heat sterilization process cause destruction of micro-organisms by denaturation of macromolecules.

Heating an article is one of the earliest forms of sterilization practiced. Moist heat sterilization processes sterilize using hot air that is heavily laden with water vapor, which plays the most important role in the sterilization.Boiling a sample for 30 minutes or more will kill virtually all vegetative cells present, but will not kill spores, which can germinate shortly thereafter and resume growth. Therefore, boiling is an insufficient method to achieve sterilization.

Moist heat causes destruction of micro-organisms by denaturation of macromolecules, primarily proteins. Destruction of cells by lysis may also play a role. While "sterility" implies the destruction of free-living organisms which may grow within a sample, sterilization does not necessarily entail destruction of infectious matter. Prions are an example of an infectious agent that can survive sterilization by moist heat, depending on conditions.

To facilitate efficient sterilization by steam and pressure, there are several methods of verification and indication used; these include color-changing indicator tapes and biological indicators. When using biological indicators, samples containing spores of heat-resistant microbes such as Geobacillus stearothermophilis are sterilized alongside a standard load, and are then incubated in sterile media (often contained within the sample in a glass ampule to be broken after sterilization). A color change in the media (indicating acid production by bacteria; requires the medium to be formulated for this purpose), or the appearance of turbidity (cloudiness indicating light scattering by bacterial cells) indicates that sterilization was not achieved and the sterilization cycle may need revision or improvement.

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