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InvisiblebodhisattaMDiscordReddit
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The Importance of Venting a Pressure Cooker or Autoclave * 17
    #25493951 - 09/28/18 04:26 AM (4 years, 2 months ago)

The Importance of Venting a Pressure Cooker or Autoclave


Two test have been conducted so far one with a presto 23q and one with an AA 25x sterilizer.


A nearly new presto 23q pressure cooker was used for this test

There was one quarter taped to the weight.
The first trial I put the lid on the cooker with 1q of the hottest tap water I have inside. Put the weight on the lid immediately. no venting done. Turned the stove to 10.
As soon as the weight started to jiggle I killed the heat.


244F ±2F

The second trial I put the lid on the cooker with 1q of the hottest tap water I have inside. I turned the stove to 10. vented for 10m after steam appeared from the vent. put the weight on and as soon as the weight started to jiggle I killed the heat


258-259F ±2F

For both test runs I put the trivet in and two empty mason jars upright with no lid to stand the thermometer on.
In both tests the needle on the gauge got up in between 17-18psi
at 18psi I shouln't have seen such high temperatures on the thermometer but considering the thermometer is calibrated to NIST and the gauge on the presto is from china I'm going to go with the gauge being a hair off on the low side. The gauge is accurate to one scale division so ±2F

This may seem like a small difference but the difference is huge in terms of sterilization effectiveness. Not only is the temperature lower but the lower heat capacity of air compared to steam means you are not as energetically pumping the heat into the media being sterilized. Steam has a high latent heat.

Steam has more "heat torque" than air
Quote:

Latent heat can be understood as heat energy in hidden form which is supplied or extracted to change the state of a substance without changing its temperature.



steam forces way more energy into the media than air does.


Quote:

Because of a much higher heat capacity, steam and liquids transfer heat more rapidly than air. For example, the hot air inside an oven at 200 °C (392 °F) will not immediately burn your skin, but the steam from a boiling kettle at 100 °C (212 °F) will scald skin almost instantly and feel hotter, despite the steam (and water) in the kettle being at a lower temperature than the air inside a hot oven. Thus the internal temperature of material in a pressure cooker will rise to the desired value much more quickly than if it were in an oven.




Quote:


It is very important to ensure that all of the trapped air is removed from the autoclave before activation, as trapped air is a very poor medium for achieving sterility. Steam at 134 °C can achieve in three minutes the same sterility that hot air at 160 °C can take two hours to achieve




Quote:

Effective moist-heat sterilization depends on having saturated steam conditions. When air is present in the system to be sterilized, saturated steam temperature and pressure conditions no longer apply.

The air dilutes the steam and a lower temperature than expected is imposed at a given pressure. Trapped pockets of pure air completely prevent steam contact and provide dry-heat sterilization conditions.





Test 2 with an All American 25x sterilizer with the vent tube removed

Using no basket just the trivet rack. Starting with hot ~140F tap water for both runs.

for both runs I'm going to bring it up to 15 psi and toggle the on off switch to keep it at 15psi for 5m. Then kill it.

For the venting run ill vent 10m. Get to 15m and hold it there 5m then kill it. For the non vent run I'm putting the lid on with the toggle closed and skipping the venting entirely

Interesting enough is that with the toggle closed from the beginning (0 venting) I could stand to hold my hand on the lid with pressure registered on the gauge. Because air was getting compressed before the water was even boiling. And once it started to boil it quickly compressed air giving an abnormally high pressure for a low temperature.




Got up to 15.5-16psi kept it there 5m before shutting down. This is what I got off the thermometer. Very interesting.

212±2F

Here's the reading from the vented run. Also hit close to 16 psi during the 5m hold.

252±2F

that's a 40F difference and there was a 5 minute hold just to make extra sure the thermometer registered the temp at 15psi.


The toggle holds in air better than the jiggle weight on the presto. so the presto sort of vents itself during the run, the toggle on the AA really trapped the air in it seems.




Vent your pressure cookers.


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Re: The importance of venting a pressure cooker [Re: bodhisatta]
    #25493961 - 09/28/18 04:30 AM (4 years, 2 months ago)

Thanks for the reminder bod. Its nice to see experiments like this. I should shoot this to mateah :hehehe:


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Re: The importance of venting a pressure cooker [Re: JHOVA]
    #25493966 - 09/28/18 04:32 AM (4 years, 2 months ago)

I'll eventually be doing the test a few more times and with different cookers and weights to establish consistency and reliability.


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Re: The importance of venting a pressure cooker [Re: bodhisatta]
    #25493973 - 09/28/18 04:36 AM (4 years, 2 months ago)

The Bod Man cometh!! Nice thread brotha! :rockon:


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Before you start...Do you have a Pressure Cooker and a Dehydrator? I highly recommend getting both!


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Re: The importance of venting a pressure cooker [Re: Tormato]
    #25493976 - 09/28/18 04:38 AM (4 years, 2 months ago)

I've wanted to see this for myself for so fucking long. For $60 dollars I don't know why I waited so long


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Re: The importance of venting a pressure cooker [Re: bodhisatta] * 1
    #25493984 - 09/28/18 04:41 AM (4 years, 2 months ago)

Quote:

bodhisatta said:
I've wanted to see this for myself for so fucking long. For $60 dollars I don't know why I waited so long



I might know why :lol:

:customgrow420:  :smokinacandycane:  :doublejointed:


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Re: The importance of venting a pressure cooker [Re: Tormato]
    #25493992 - 09/28/18 04:43 AM (4 years, 2 months ago)

:bonghit::rofl:


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Re: The importance of venting a pressure cooker [Re: bodhisatta]
    #25494001 - 09/28/18 04:49 AM (4 years, 2 months ago)

I was literally just reviewing/revisiting your pressure cooker tek to ensure that my process is on point and I always stress the importance of venting. Whenever I learned how to properly vent, my success rate dramatically increased.

Thanks again! :raisemyglass:


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Re: The importance of venting a pressure cooker [Re: bodhisatta]
    #25494005 - 09/28/18 04:50 AM (4 years, 2 months ago)

Quote:

bodhisatta said:
:bonghit::rofl:



:bongload:  :cool:


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Re: The importance of venting a pressure cooker [Re: bodhisatta]
    #25494029 - 09/28/18 04:58 AM (4 years, 2 months ago)

I been venting since first run, 5 or so runs of oat jars, so far with 0% contamination. Than you for another great write up. :rockon:


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Re: The importance of venting a pressure cooker [Re: Johnny.rotten]
    #25495156 - 09/28/18 05:33 PM (4 years, 2 months ago)

I'll try this with the 25x Tonight if i get time.
Stupid AA sterilizer takes so fucking long to get to venting and pressure even if I start by pouring boiling water in it. I almost want sell it and buy 3 new presto cookers plus a couple burners to run em and my own control+thermostats. It's nice not having to babysit it since it has a thermostat but it takes like 4 hours to do a 2 hour cook


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Re: The importance of venting a pressure cooker [Re: bodhisatta]
    #25495701 - 09/28/18 09:55 PM (4 years, 2 months ago)

To give an indication how big of a difference this is: 10 minutes at 258F/126C would require 63 minutes at 244F/118C to provide equivalent sterilization. Six times longer!



10*10^((126-118)/10). Z assumed to be 10C.


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Re: The importance of venting a pressure cooker [Re: teladi]
    #25495718 - 09/28/18 10:01 PM (4 years, 2 months ago)

That's assuming that there is saturated 100% steam conditions at 244F. Since some of it is air it would actually take even longer than 63m.


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Re: The importance of venting a pressure cooker [Re: bodhisatta]
    #25495744 - 09/28/18 10:11 PM (4 years, 2 months ago)

So essentially this is to evenly distribute the steam throughout the media to ensure FULL STERILITY. Correct?

I have noticed ONE run of jars in which I just capped the PC with the Weight, that I saw contamination.

I will be steaming from now on to ensure FULL STERILITY...

Thanks Holmes.


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Re: The importance of venting a pressure cooker [Re: TheAtlantean]
    #25496031 - 09/29/18 12:01 AM (4 years, 2 months ago)

:billymaythumbup:


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Re: The importance of venting a pressure cooker [Re: MrSturgill]
    #25496111 - 09/29/18 12:26 AM (4 years, 2 months ago)

:takingnotes:


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Re: The importance of venting a pressure cooker [Re: Zero Nowhere]
    #25496287 - 09/29/18 01:43 AM (4 years, 2 months ago)

:hereyougo:


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Re: The importance of venting a pressure cooker [Re: Failboat]
    #25496304 - 09/29/18 01:49 AM (4 years, 2 months ago)

:super:

The temp differences is going to be the difference between killing everything in the jar (fully sterilized) and getting contams all the time because the sterilization was insufficient.


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Re: The importance of venting a pressure cooker [Re: Zero Nowhere]
    #25496330 - 09/29/18 02:07 AM (4 years, 2 months ago)

Interesting.  I’ve had a suspicious amount of jars fail on me.  I have an AA 21.5 qt that is probably 30 years old or more.  I let it steam for 10-15 minutes, directions say 7-10.  Think maybe I’ll try a longer steam venting. 
Thanks for the info Bod!


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Re: The importance of venting a pressure cooker [Re: SunnyDayze]
    #25496805 - 09/29/18 05:42 AM (4 years, 2 months ago)

My pressure cooker doesn't vent properly with the 8-9 big spawn bags that I pack into the autoclave and I cook then for 6 hours. I've never vented, even when cooking agar for just 1 hour. I have no contamination issues until after the 1st flush but rarely get a 2nd. So who knows, maybe I'm not killing everything.


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