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Is this pasteurized substrate ok?


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#1 MushyTushy

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Posted 22 April 2021 - 02:00 AM

I pasteurized a straw and manure based substrate for about 3 to 4 hours at around 160°F. It's been sitting in jars for about a week. I've left them because I read that letting them sit longer allows the microbial content to multiply which helps reduce chances of contamination.

I looked at them today and they seem to have this whitish appearance now. They smell fine but I'm worried about whether or not I should use them. I plan on making more regardless but I'm wondering do they look contaminated. I'd say they may be a tad on the drier side for my use but still feel moist.

This is my first time working with straw so all feedback is welcome. There are also no additives like gypsum or lime which I've read wasn't necessary for this purpose.

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#2 Sidestreet

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Posted 22 April 2021 - 03:57 AM

Would it be possible to get a clearer picture?  With manure and straw, you want to see some powdery white because that indicates the presence of actinomycetes, a helpful type of bacteria.  If you follow that link, scroll down to "The Decomposer Actinomycetes".

 

Or it could just be a contaminant mold.  I've never heard of actinomycetes forming after pasteurization, but then again people usually spawn their substrate soon than you have.  Usually it's been more about selecting manure with the powdery white on it before pasteurization.

 

You could try spawning--it sounds like you pasteurized correctly...



#3 Jrotten

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Posted 22 April 2021 - 08:46 AM

Assuming you pasteurized right and they’ve been sealed you’re likely fine, I don’t see anything that screams contamination to me, but that means nothing. With straw and manure I like an initial temperature around 190F and then I let them rest around 160F-165F for a few hours, but if you allowed plenty of time for the core temperature to hit 160 you’re likely fine. Only you know what it looked like before and after.

#4 MushyTushy

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Posted 22 April 2021 - 09:40 AM

Thanks for the feedback. I've never heard of anyone have an initial temperature of 190 with straw. Any particular reason why you do that JR?

I have some spawn that I'll do a test run on with that substrate and see how it goes. Maybe letting it sit a week is a bit too long.

#5 MushyTushy

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Posted 22 April 2021 - 09:44 AM

And thanks for the info about Actinomycetes.

Sorry for the double post. I guess I can't edit my previous reply.

#6 Myc

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Posted 22 April 2021 - 09:53 AM

That looks like mold to me.

I like to inoculate as soon as the core temperature of the substrate is suitable.

Letting it sit for a few days at room temp will allow mold and bacteria to germinate. I would pasteurize another batch and inoculate once the core temp is below 80*F.

 

Nothing wrong with an experiment. You just have to be prepared to fail - and learn something in the process.



#7 TVCasualty

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Posted 22 April 2021 - 01:44 PM

 I've left them because I read that letting them sit longer allows the microbial content to multiply which helps reduce chances of contamination.

 

Where did you read that?

 

I'm genuinely curious. It's not true, by the way.

 

I'd start over with fresh manure. I agree with Myc that yours is moldy (and that it's best to inoculate pasteurized subs ASAP after they cool down).

 

When I pasteurize, I bring the sub up to ~170℉ and keep it within 10 degrees for about 12 hours. I highly recommend that anyone pasteurizing manure or straw do the same.

 

I let it cool down slowly so it usually stays above 150 for another 6-12 hours depending on how much I'm cooking (my rig holds a lot of mass). When I started doing that (and using a better source of straw for my straw subs) my contamination rates dropped to somewhere around one tray contaminating before the first flush out of dozens; it got low enough that I quit bothering to keep track.

 

Stick with it and the fruits will come. Fungi seem to like to test our commitment (and how...). Passing that test is absolutely worth the trouble. It took me over a year and many attempts to get a single mushroom. I do not regret a moment of that seemingly endless parade of failure since it taught me more than I could ever describe.

 

Good luck!



#8 Jrotten

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Posted 22 April 2021 - 07:42 PM

I let it hit 190 after reading a lot about the process of making commercial mushroom compost.  I use a microwave so i hit that 190F in 5 minutes in the containers I use.  Water turns to steam and hydrates the straw in the process then it goes straight in the oven at 170F which is the lowest setting.  The temperature comes down very fast.  At half an hour and generally beyond the sub is between 160-170 taking multiple measurements.

 

The high initial temperature is to get an immediate kill back even into some of the thermophiles, the time at temperature allows some amount of  beneficial organisms to recover and even grow back.  I've seen people talk about leaving it to keep for 4-5 days, and they are better growers than me, but what I understand is that it's much better to have a slow cool down, especially in the 120F-140F range.  

 

The temperature does 2 things: it kills bacteria, fungi, spores, insects, etc, but it also encourages proliferation of other organisms going through various temperature ranges.  Most human pathogenic bacteria for instance will be dead at 120F for some time, while more thermophilic bacteria will be growing at optimal temperatures.  Then at growing/room temperatures we want minimal time before inoculation so that things that want to compete at the optimum temperature are out competed by our culture having a big headstart.

 

I've spent years getting questionable pasteurization results until I switched to my current method of flash heating in the microwave and finished in the oven for hours.  It also helps control hydration of the sub.  I've done a lot of other types of pasteurization, but for straw and manure to grow pans the way I do, this is the only thing that successfully gets me multiple flushes instead of contamination before harvest. 






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