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Old 07-08-2012, 07:40 PM   #1
Larso
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Default Is 7psi enough for for an autoclave?

I, I recently bought a pressure cooker to use as an autoclave for slanting. It cooks at 7psi. Is this enough pressure for autoclaving? Can anyone tell me how long I need to cook for at this pressure to sterilise my gear?

Thx

L

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Old 07-09-2012, 01:22 AM   #2
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That will not be sufficient to truly "sterilize" items. It will get them very clean however, and cooking things like agar and media for 30 min at 7 psi will likely give you no problems. I would try it out before going and buying something else.

If you do have problems, you can always "Tyndallize" them instead of autoclaving. Tyndallizing is where you heat something up to boiling and then let cool for 3 consecutive days, which gives results similar to autoclaved items. The 1 day between boilings allows the bacterial "endospores" (the part that survives regular boiling) a chance to germinate, and then when you boil next it kills the bacterium. It is more labour intensive, but works great.

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Old 07-09-2012, 11:57 AM   #3
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Thanks theredben, found a crack on the handle of my new pressure cooker so brought it back an got a larger one that cook at 11.6 psi and received €6 back as it was cheaper. Assume this is good enough for autoclaving?

Thx

L

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Old 07-09-2012, 12:16 PM   #4
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Quote:
Originally Posted by Larso
Thanks theredben, found a crack on the handle of my new pressure cooker so brought it back an got a larger one that cook at 11.6 psi and received €6 back as it was cheaper. Assume this is good enough for autoclaving?

Thx

L
For proper autoclaving/sterilization, the minimum pressure required (for water, though wort is almost the same) is 15psi. 11.6psi should be better than just boiling, but it shouldn't achieve true sterilization.

Sorry to be the bearer of bad news. If you really want to have a true autoclave capability, I hope you can return the one you have.
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Old 07-11-2012, 10:27 AM   #5
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Quote:
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For proper autoclaving/sterilization, the minimum pressure required (for water, though wort is almost the same) is 15psi. 11.6psi should be better than just boiling, but it shouldn't achieve true sterilization.

Sorry to be the bearer of bad news. If you really want to have a true autoclave capability, I hope you can return the one you have.
Thanks Emjay, was just reading the manual with it and it says 'nominal pressure 11.6, maximum pressure 15psi' any idea what exactly that means?? It also says only to put in items that can withstand 130degC?

Go on! Tell me what I want to hear!!!

Thanks

L
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Old 07-11-2012, 11:28 AM   #6
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If you want to sterilize, you need boiling water or steam at 15 psi for 15 minutes. Boiling water at 15 psi is 250F. I give it 20 minutes to make sure everything is up to temp evenly.

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Old 07-11-2012, 12:01 PM   #7
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Don't forget to let the steam build and vent for a few minutes before starting your count down as well. Mushroom growing forums are a good place to find info on using pressure cookers for sterilization. I grow shiitakes from time to time and got really great info in books on growing them. Yeast is a fungi and so the culture of yeast is similar in many ways.

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Old 07-11-2012, 10:12 PM   #8
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Quote:
Originally Posted by Larso View Post
Thanks Emjay, was just reading the manual with it and it says 'nominal pressure 11.6, maximum pressure 15psi' any idea what exactly that means?? It also says only to put in items that can withstand 130degC?

Go on! Tell me what I want to hear!!!

Thanks

L
I suspect that means at 15psi it starts venting a safety valve. Hard to say.
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Old 07-11-2012, 10:34 PM   #9
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The best answer I can find on the matter is that 11.6psi is what you can expect under normal conditions, which would indicate it's not good enough.

I'd suggest calling the manufacturer if you want to be sure what they mean by nominal pressure. Don't tell them why, though, as CS reps often just tell you want they know you want to hear.

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Old 07-11-2012, 10:35 PM   #10
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Buy some autoclave tape; it's tape that changes color once it hits sterilization temperatures. Stick it on whatever you want to sterilize, let the pressure cooker rip for an hour, and see what happens.

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