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Re: Cant get collapsed bags by end of pc cycle [Re: TravelAgency]
    #25580772 -

TravelAgency said:
I'd guess if all your contams are coming in through the top there might be an issue with your seal. Are you using an impulse sealer? If so are you keeping it closed for an extra 5-10 seconds after you hear the click? If not Id put my money on that being your issue.

  Ive also had difficulties with inflating bags - especially sawdust bags - in the PC. I've solved this problem- and the problem of them occasionally melting - by wrapping them in a towel. I can only fit 2 6lbs bags at a time anyway so that extra space isnt wasted.


Sometimes I use an impulse sealer, sometimes I dont, I dont like mine very much. At any rate, RR says he closes his bags with just electrical wire (which I do sometimes), never uses an impulse sealer, and gets away with it.

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Re: Cant get collapsed bags by end of pc cycle [Re: vsoares]
    #25580789 -

Yes they sure will. I dont know any commercial producers that use any larger than .2 for grain spawn. I know MorePies toyed with it a little bit, maybe he will chime in.


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Re: Cant get collapsed bags by end of pc cycle [Re: SHROOMSISAY01]
    #25580807 -

SHROOMSISAY01 said:
Sorry I will be a little more careful with my jokes next time. I actually know nothing about thermal dynamics and I actually had to look up how to spell it. What I do know is from experience. I have never opened up my PC quickly but every time I open my 55-gallon steamer right after a cycle is done my top bags are loose but. If I wait for a day or two they are all sealed perfectly. The OP mentioned equalizing the pressure so I assume he is releasing the pressure which is his problem.

What I believe is happening when you release quickly is the bag cools down much quicker than the spawn and evaporates any water on the plastic and never seals. When you let it cool down slowly it slowly pulls the bag together and does not evaporate the moisture between the two pieces of plastic the slow cool allows a tiny amount of water to remain, which, seals the bag then after it is sealed the further cooling of the spawn causes a vacuum and seals and evaporates the rest of the water on the bag.

I believe the key here is flash evaporation. Open quick and it will flash evaporate the moisture on the bag or actually in between the two pieces of plastic of the bag where it should seal.


Because my autoclave pulls a vacuum by the end of the cycle, I have to equalize the pressure before opening it, by releasing the valve, otherwise the pressure differential will keep the lid shut.

Actually I am a physicist myself (but never worked in the area), and as far as I understand, what happens is this:

1) In the beginning, there is "atmospheric" air inside of the pc, just like outside.

2) As the pc is heated, the pressure inside it increases, forcing the air out, which is the same as saying that the air density (number of molecules of O2, N2 etc per unit volume) inside it is reduced. Because the vent valve is open, the pressure differential is always very small, as the the air keeps being released from the pc chamber.

3) When we reach the boiling point of water, H2O molecules start coming out the the liquid phase at a fast rate, filling the pc chamber and, at the same time, pushing the O2, N2 etc molecules out of the pc, further reducing the density of gases inside the chamber.

4) If we leave the valve open for long enough, allowing the steam plus air mixture to vent abundantly, there will be very little gas molecules left inside the autoclave, which will be mostly filled with steam.

5) We then proceed to close the vent valve, and as the chamber is further heated, more steam comes out of the liquid phase, increasing the pressure inside the chamber.

6) The pressure raises to the point where the pressure differential between the inside and the outside of the chamber is balanced by the weight at the top of the air vent hole. At this point, the system is in some sort of equilibrium, the temperature is stabilized, and the pressure inside the chamber is basically constant.

*) During steps 2-6, because the heating up of the air inside the bags is slower then the heating up of the air inside the pc, there is a pressure differential between the inside of the chamber and the inside of the bags, which forces the air from the bags out, helping reducing the ammount of gas molecules inside the bags.

7) At the end of the cycle, he pc starts cooling of, and the pressure inside the chamber falls. At this point we have basically steam filling the chamber, and the reduction in temperature means that some of those molecules will return to the liquid phase (reducing the pressure), wherever they happen to be (inside the bags, for instance), and everything will get pretty wet. If the cooling off is too quick, there might be a significant pressure differential between the inside of the bags and the pc chamber itself, but now in the opposite direction that was seen during the heating up, which might cause the bags to inflate (instead of collapsing further).

8) Because we have so little gas molecules inside the pc, when we return to room temperature, the pressure inside the chamber will be smaller then outside (if the pc is completely sealed, which is the same as to say, "pulls a vacuum"). If the pc does not pull a vacuum, then air will seep inside the chamber gradually as the pc is cooled. If the inflow of air is slow (which will happen if the cool down is very gradual), then the gases will fill the chamber, but might not be able to get inside the bags. The bags will keep "collapsed".

As I understand, the bags get collapsed during the heat up phase. During the cool down, they might inflate back or not, depending on what you do, but I dont think they collapse during that part of the cycle.

An important point to make here, if I did not myself so clear, is that what makes the bags shrink (or inflate) is the pressure differential between the inside of the bag and the inside of the pc chamber, and not the difference in pressure between the inside of the chamber and the outside of the pc (atmospherc pressure). So in fact our system actually has 3 "chambers": the outside of the pc, the inside of the pc (and outside of the bags), and the inside of the bags.

So as I see it, opening the vent valve at the end of the cycle has no possible benefit, and it might screw everything up by letting the bags inflate. In theory I suppose thats what happens. I guess I will try putting some weights on top the bags to see if the extra pressure will help the bags to deflate further during the heating up (and also, make it harder for them to inflate back during the cool down).

Edited by vsoares (10/31/18 06:52 AM)

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Re: Cant get collapsed bags by end of pc cycle [Re: TravelAgency]
    #25580849 -

TravelAgency said:
Yes they sure will. I dont know any commercial producers that use any larger than .2 for grain spawn. I know MorePies toyed with it a little bit, maybe he will chime in.


Sure ppl use A patch bags for spawn.  It is better for mold bc more air means it will more likely sporeulate .  Then you can see it if it's there


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Fiery Fungi (like us on faeboo)

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Re: Cant get collapsed bags by end of pc cycle [Re: drake89]
    #25580857 -

drake89 said:
TravelAgency said:
Yes they sure will. I dont know any commercial producers that use any larger than .2 for grain spawn. I know MorePies toyed with it a little bit, maybe he will chime in.


Sure ppl use A patch bags for spawn.  It is better for mold bc more air means it will more likely sporeulate .  Then you can see it if it's there


I see people in Thailand use cotton plugs on top of their grain jars. I think people in the US also use cotton or polyfil plugs, dont they? Is a polyfil plug better than a 0.5 micron filter patch?!

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Re: Cant get collapsed bags by end of pc cycle [Re: vsoares]
    #25580866 -

In my opinion, yes- however this comes mostly from my understanding of other peoples experience not my own trials. I'd say its worth a shot if you can get just a clutch of bags - run them side by side to the ones you already have and see if thats the difference. And please share your results!


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Re: Cant get collapsed bags by end of pc cycle [Re: vsoares]
    #25580874 -

To further ellaborate on my analysis of the pc cycle:

There is a diference if you vent the chamber or not at the end of the cycle. If you dont vent, there will be many more water molecules inside the chamber in the form of steam, which means things will get wetter as they cool down. On the contrary, if you do vent the chamber, there will be less steam to cool down, and you should get drier bags at the end of the cycle.

Also, as my analysis indicates, if the valve is open after the chamber reaches 0 psi, there will be no more "bad" pressure diferential between the inside of the bags and the pc chamber, because the pc chamber will be always at atmospheric pressure (from that point on). If the bags are already "sealed" at this point (which means, if they are collapsed with bag sides "glued" to each other), and as the steam inside the bags cool down and the pressure inside them falls, there might be further tightening of them. If the bags are not sealed, though, air will just seep inside of them.

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Re: Cant get collapsed bags by end of pc cycle [Re: vsoares]
    #25580891 -

I'm still curious as to how you seal them before PCing? Do you use an impulse sealer?


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Re: Cant get collapsed bags by end of pc cycle [Re: TravelAgency]
    #25580895 -

TravelAgency said:
I'm still curious as to how you seal them before PCing? Do you use an impulse sealer?


I dont seal them at all before pcing. I just fold them over.

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Re: Cant get collapsed bags by end of pc cycle [Re: vsoares]
    #25580961 -

bingo. While presealing isnt necessary for sawdust bags, in my experience it is not wise to do so with grain, and this could also be your inflation problem. Do you seal after inoculation?


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Re: Cant get collapsed bags by end of pc cycle [Re: TravelAgency]
    #25581119 -

Yes sometimes I seal after inoculation, sometimes I just twist a piece of eletric wire on top of it. I think RR does the same and gets zero contams. He also doesnt seal bags prior to pcing.

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Re: Cant get collapsed bags by end of pc cycle [Re: vsoares]
    #25581137 -

RR, as amazing as he was - was 15+ years ago. After you inoculate, seal. Every single time. With your contams coming in through the top, forget everything else I've stated so far. Start sealing and see if your contams go away. I'd be willing to stake my reputation on that being your vector. If you already have an impulse sealer, theres no excuse not to use it. If you dont have one, save up 30 bucks and get one on ebay.The addition of that tool changed my game entirely. Speed, security, sanity - and no top fruiting were all pros with literally zer0 cons. Mycology isnt really suited to cutting corners.


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Re: Cant get collapsed bags by end of pc cycle [Re: TravelAgency]
    #25581610 -

I use .5 micron on my spawn bags without a problem many people do. I do understand it is not recommended but it can and is done by many people.

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Re: Cant get collapsed bags by end of pc cycle [Re: TravelAgency]
    #25581799 -

TravelAgency said:
RR, as amazing as he was - was 15+ years ago. After you inoculate, seal. Every single time. With your contams coming in through the top, forget everything else I've stated so far. Start sealing and see if your contams go away. I'd be willing to stake my reputation on that being your vector. If you already have an impulse sealer, theres no excuse not to use it. If you dont have one, save up 30 bucks and get one on ebay.The addition of that tool changed my game entirely. Speed, security, sanity - and no top fruiting were all pros with literally zer0 cons. Mycology isnt really suited to cutting corners.


Ok, but you talked about pre-sealing the bags before pcing. Wont they explode? You seal the bag, pc, then cut the seal open, inoculate, and seal again?

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Re: Cant get collapsed bags by end of pc cycle [Re: vsoares]
    #25581861 -

No they won't explode. Yes exactly the method you describe,  push all air out when you seal prior to pc.


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Re: Cant get collapsed bags by end of pc cycle [Re: Quadman]
    #25581987 -

.2 micron is not meant to be sealed b4 PCing. But that does not mean you can't do it. If the bag bursts, it would be for that reason. .5 micron can be sealed b4 PCing with no problem. I use .5 micron with no problems for spawn and sub alike.

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Re: Cant get collapsed bags by end of pc cycle [Re: SHROOMSISAY01]
    #25582026 -

It's .2 if it looks like a paper patch. It's. 5 if it looks like the stuff in a bandaide.


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Stop talking about being enlighten. Crybabies, bitches, and people worried about ratings can never reach enlightenment!  NEVER!

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Re: Cant get collapsed bags by end of pc cycle [Re: Quadman]
    #25582103 -

I have yet to have a bag burst in the PC unless the bag was touching one of the lower regions of the autoclave.

Quadman said:
No they won't explode. Yes exactly the method you describe,  push all air out when you seal prior to pc.


Yep, exactly as my good friend Quad said. How have you been buddy? :wave:

Like I said, presealing is not necessary, but I wouldnt advise it. Especially in a PC - a Steam Sterilizer will be much more forgiving, but still wouldnt advise.

But you must - must seal after inoculation.


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Re: Cant get collapsed bags by end of pc cycle [Re: TravelAgency]
    #25582142 -

Interesting discussion and great arguments and theories :cheers:

However I still don't get from vsoares' hypothesis what the actual consequences are of slow cooling and pressure equalization / small pressure differential vs fast cooling and pressure equalization / large pressure differential.

And also how the air might get into the bag reinflating it in some cases but not others.

Shroomsisay's cool idea about the water playing a role in the seal created which could be that factor in whether air is allowed to get back in or not upon cooling.

Now that I think about it, what may also play a role is how the plastic bag cools down. In my experience it retains the shape it got during PCing which is not surprising since you can get kinda close to melting range, probably enough for mild thermosetting.
I say this because I tend to put my bag on a crushed can on the bottom of my PC to elevate it. I do have some elevated plateau to get above water level in my PC but it's not enough if I do a long PC cycle of wood and occasionally a shitload of water manages to escape compared to other times so i add enough.
Point is: this shapes the bag bowed and this persists quite a bit.

What compounds this is I don't really think you create a true sealed "vacuum" (i.e. underpressure), there is nothing suggesting to me when I open the bag for inoc that I break that seal after which the bag reinflates a bit like a popping lid of a jar. You would have to be seeing a moment when the seal breaks and there is a sudden rush of air entering.

I hadn't heard earlier about you equalizing the pressure of the autoclave like that (i thought you didnt use the valve and just let it equalize gradually.. and I still don't think you have mentioned how much time you allow to pass before you do open up the autoclave.

So I guess I do agree with the suggestion earlier that this is where it goes wrong, that you don't leave enough time for cooling (could take annoyingly long with an autoclave?) and that the pressure equalization is too fast perhaps. Is there no way to do it incrementally? If so I would do it as incrementally as possible.

Some gusts of air entering is one thing but if the bag reinflates too and sucks up the gusts of air that could be the big problem indeed. You may need to improvise some way to either avoid the sudden changes in temp and pressure and if not, protect your bags from the air rushing in somehow.

Is there no way to make sure that the air getting back in the autoclave is sanitized? Or could it be fitted with a custom valve (safely of course!) to slow down the air current?

I guess i underestimated the general importance of taking it a bit slow after a PC cycle and that my situation probably is much faster (but still gradual) in the equalization so i don't get these problems I guess. So you're right shrooms

Shroomsisay actually in hindsight it is kinda funny how i missed the joke (thats what happens without nonverbal communication or emojis haha) and went into the physics.

I only recently started sealing after inoc of bags, remembering that i have a ghetto vacuum sealer... other times I just do two small folds at the top and put on clothespins. Occasionally a little tape to make sure it stays that way. Definitely will only seal from now on if i can trust the sealer to seal the deal.

I don't know how you are using that electrical wire, but it would have to be pretty terribly to get consistent contams on top while i am fine with the folds and clothespins.

But yea if i get to the point of tumbling my bags to mix like Gr0wer then you can bet your baby's beehive that I will be sealing the bag :wink:


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    • Edited by Solipsis (10/31/18 04:29 PM)

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    Re: Cant get collapsed bags by end of pc cycle [Re: Solipsis]
        #25582362 -

    Hey TA:hi:

    I should add a disclaimer,  I've never sealed .2 micron bags and PC them .

    There is an aspect that is often overlooked. Everyone lives in different regions and different structures. My 100 year plus old home is a mold magnet. Couple that with living in the Midwest and it seems a recipe for disaster. I will always seal my bags when cooking. A 941AA autoclave is what is my main method.

    OP stated that he draws a vacuum. If opening while under vacuum, would suggest  filtering the intake valve with alcohol rag.

    I've had decent results watching the cool down and as soon as cooker has cooled to zero pressure ,opening valve. This prevents a large in rush of air (and contaminates). Still does not keep sterile .

    Best to just open at flow hood if it pulls vacuum.:shrug:


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