A pressure cooker can be used to sterilize BRF substrate. Pressure cookers are also bulky, reasonably expensive and very difficult to locate for some (you can’t go pick up a cheap pressure cooker from the local big ‘Mart or thrift store in many other countries).
The thrust of this document is a sterilization process called Fractional Sterilization (hereafter FS). This process is also called Tyndallization (as it was discovered by J. Tyndall in the mid 1800’s). This is not a new idea/process. The Tyndallization process predates home pressure cookers by over 100 years.
The ideas that make FS/Tyndallization work are very easy to understand:
- Virtually all living contaminants are killed by boiling/steaming temperatures. If it is alive/growing, 60 minutes exposure to steam temperatures will kill it.
- Most endospores (contaminant “seeds”) are NOT killed by boiling/steaming temperatures. Four hours of steam (at regular pressure) will not kill some very common bacterial endospores.
- Given time and proper conditions to “hatch” and begin growing, even the toughest endospore becomes a (relatively) delicate living microbe which can be destroyed by steam heat at regular atmospheric pressure.
- A process that germinates endospores and then destroys the resulting living contaminants can actually be more effective than pressure cooking (some endospores can survive 60 minutes @ 15psi in a pressure cooker).
Boiling/steaming temperatures can’t kill endospores, but once they germinate/hatch, boiling/steaming temperatures can easily destroy the resulting microbial life.
Please pardon the redundancy of those last two paragraphs, but I want to make sure you understand this process so you can have confidence in it working. Also, please remember, FS is used by professional culture labs when dealing with medias that don’t stand up well to high temp/high pressure sterilization procedures. Boiling is already well established as a preferred method of producing sterile liquid culture media (boiled sugars don’t carmelize and drop out of solution).
The actual process of using FS/Tyndallization to sterilize BRF is:
- Prepare BRF jars and let them sit at room temperature for 24 hours.
- Steam the jars for 60 minutes.
- Wait 24 hours and steam the jars for 60 minutes.
- Wait 24 hours and steam the jars for 60 minutes.
A 4 day process involving three 60 minute steam baths guarantees sterilized jars, even with the lowest quality/dirtiest starter rice. As will be detailed later, it is also possible to use this process (with 90 minute baths) to sterilize popcorn.
It is VERY important not to go longer than 24 hours between steam baths. If you go much longer, the nasties inside will become highly established (and harder to kill). Also, some bacteria will begin producing new endospores at around 30 hours. The 24 hours between steam treatments is critical to success. If you miss the steaming window by more than 4 hours, dump the jars and start again.
Edited by BuckarooBanzai, 30 August 2009 - 01:34 PM.