Instant Pot Sterilization
“Only the Instant Pot brand pressure cooker was able to inactivate G. stearothermophilus endospores, which indicated that it would be the most appropriate choice for a laboratory pressure cooker.”1
In the study referenced above they tested the 8-quart IP-DUO80 Instant Pot. This device has the same pressure and temperature ratings as the smaller 3-quart DUO Mini and the 6-quart IP-DUO60 v3 version that we use. There is a newer model, Instant Pot Max, that gets up to and sustains 15psi. Theoretically this would be much more effective at sterilization than the DUO models. If you have the Max please investigate its temp and pressure ratings to help you determine how long you need to run it for to achieve sterility. The rest of this page is about the DUO.
The recommended temperature and pressure for steam sterilization is 121C at 15psi for 20-60 minutes.2 However the Instant Pot Duo only reaches 115-118°C at 10.2-11.6psi.1 3 Because of this the “standard” 20-60 minutes will be inadequate for sterilization. The study that evaluated commercial electric pressure cookers stated that it took a full 150 minutes for the pressure cooker to inactivate G. stearothermophilus endospores, which are of the most resistant to sterilization.
The Instant Pot should be operated for at least 150 minutes to achieve sterility.
Can math back up this data on how long to run the Instant Pot for?
Accepted industry standard Z value for steam sterilization is 10°C.4
If the recommendation is to use 121°C for 20-60 minutes, then operating at 111°C we’d need to run it for 200-600 minutes. This is looking on par.
| D | Time (minutes) |
|---|---|
| D111 | 200-600 |
| D115 | 80-240 |
| D121 | 20-60 |
Sterilization cycles should be validated to ensure that the survival of the most resistant microorganisms is no greater than 10-6 under specified operating conditions and parameters2
A 1°C variation in the sterilization temperature causes an increase (or reduction) of the sterilization rate by a factor of 1.26, i.e. 26%5
So yes, the maths back up the study’s claim of 150 minutes. You probably shouldn’t go any less than that, and you def could go more, up to 240.