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uncletammy
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Registered: 05/23/09
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Calculating Sterilization Times
#13022234 - 08/08/10 03:15 PM (13 years, 9 months ago) |
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Can anyone provide links to information about the method for calculating sterilization times. I'm specifically interested in steam sterilization but I know they are all fairly closely related so all information is appreciated.
I would like to not only learn the mathematical formula for such calculations but also learn some of the underlying physical principles behind the math. I want to know more about relationship between substrate temperature and sterilization time so I can calculate trade offs between the two. Thanks!
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uncletammy
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Re: Calculating Sterilization Times [Re: uncletammy]
#13031614 - 08/10/10 01:12 PM (13 years, 9 months ago) |
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sadness...
:-(
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Mephistophelian
Quasi Hob-Nobbery



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Re: Calculating Sterilization Times [Re: uncletammy]
#13031659 - 08/10/10 01:22 PM (13 years, 9 months ago) |
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Quote:
fastfred said: You can approximate each psi as equal to 1 extra degree C. Therefore 20 psi is around 5C hotter than 15C. For each 10C increase or decrease you should half or double your sterilization time.
So for 20 psi you should take the 15psi sterilization time and subtract 25%.
60 minutes usually works well for quart jars of rye at 15 psi, so you should be able to get away with 45 min at 20 psi. I would personally be a bit conservative and do 50 min.
-FF
That's the chunk I was searching for. Its not a terribly indepth mathematical breakdown but...its something closer.
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uncletammy
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Well thats at least a start. Thank!
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RogerRabbit
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Re: Calculating Sterilization Times [Re: uncletammy]
#13042739 - 08/12/10 05:40 PM (13 years, 9 months ago) |
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Trial and error beats calculation in my experience. The reason I say that is because conventional wisdom says the center of the item being sterilized needs to be at 121C for 20 minutes. However, my sterilizer never gets close to that temperature. Therefore, I gradually increased times on my 55 gallon barrel sterilizer until reaching 100% success. I've now sterilized over 5,000 six pound supplemented sawdust blocks in a row without one single contamination. I use 1 1/2 PSI for 8 hours, and the sterilizer holds 100 pounds of mushroom substrate per cycle. RR
-------------------- Download Let's Grow Mushrooms semper in excretia sumus solim profundum variat "I've never had a failed experiment. I've only discovered 10,000 methods which do not work." Thomas Edison
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BrainFarmer
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Registered: 03/06/03
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Loc: lounging betwixt lobes...
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Re: Calculating Sterilization Times [Re: uncletammy]
#13049052 - 08/14/10 12:15 AM (13 years, 9 months ago) |
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One thing to keep in mind is scaling. Scaling is the physical phenomenon in which the ratio of surface area to volume decreases as you increase the size of an object with constant proportions. When you scale up, your surface area increases as a quadratic function while your volume increases as a cubic.
"Why do I care? In English please..."
What I'm getting at is this: when you sterilize spawn, the heat moves into the jar/bag through the surface. The more surface per unit volume, the less time it takes for the interior to reach sterilization temperature. So smaller containers require shorter sterilization times. If 75 minutes works good for your quart jars, you'll want to increase this significantly if switching to gallon sized spawn bags.
These same scaling priciples also apply to the size of your chosen grain. In other words, you might want to PC popcorn a little longer than millet, if you're going for bare minimum sterilization times.
BF
-------------------- Gate Gate Paragate Parasamgate Bodhisvah
Edited by BrainFarmer (08/14/10 12:49 AM)
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blackout


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Re: Calculating Sterilization Times [Re: BrainFarmer]
#13051084 - 08/14/10 02:58 PM (13 years, 9 months ago) |
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You can look up heat transfer theory, it is quite complex though and at the end of the day it is easier to do it empirically like RR suggests.
I have adjusted my PC to run at higher pressures and so shorten sterilization times, you could also run at 25psi and then bring it back down to 15psi, i.e. preheat the grains. I have heated grains to over 100C in a microwave and then added water and it boiled violently showing it was certainly over 100C.
I saw a program on discovery where they were making heinz tinned beans, they would put a temperature logger in one tin of beans in a batch, after cooking they took it back out and said they required it to be 120C for at least 3 minutes. They did not say how long this took.
I have several jars of wheat grain which show no sign of contams, I heated them to about 95-98C for several days.
I spoke about thermal death times in this thread http://www.shroomery.org/forums/showflat.php/Cat/0/Number/1316026
This is a growlog of a grain soaked for 1 week and microwaved just once for 25mins http://www.shroomery.org/forums/showflat.php/Number/4294326#4294326 I believe most endospores would have germinated and been killed by the high temps in the microwave, the grain dried out so can go above 100C, I have measured grains at up to 135C in the microwave, and know others went higher as they burned, I also grew on those burnt grains. This thread has info on the roasted/burned grains http://www.shroomery.org/forums/showflat.php?Cat=0&Board=Forum2&Number=4398706
It is good to see you have an understanding that it takes time for materials to reach temperature. The fractional sterilization tek on this site is a joke, it is straight out of a textbook, the same textbook probably tells you that 15-20mins is enough at 15psi to sterilize. Nobody would sterilize for 15mins, and that time starts AFTER it has gotten up to 15psi. I imagine some people are sticking big jars in steam for 30mins and then these idiots wonder why it contaminated!?!
Microwaving has an even worse reputation, the wet grain is not going above 100C, if even reaching boiling at all, and you have guys heating grain for 5mins in a microwave and then say it doesn't work! Well d'uh you fucking retard...
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CheeWiz

Registered: 09/28/08
Posts: 276
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Re: Calculating Sterilization Times [Re: uncletammy]
#13069892 - 08/18/10 04:28 PM (13 years, 8 months ago) |
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Hi uncletammy; There is no uniform theory for sterilization with sets of formulas to use when sterilizing. There are just too many variables (Dead air, density, moister content, ex.) in what’s being sterilized that a new model has to be created for each special situation and this is true for all types of sterilization, chemical (ethylene oxide being the main one), gamma irradiation or steam under pressure. Sterile/sterility means the complete lack of anything living and that includes any surviving spores that may produce life. There’s no wiggle room here it’s sterile or it’s not. A sterilization technique is how we attain this state and a sterilizer is a piece of equipment that will achieve hundred percent sterility a hundred percent of the time with what’s being sterilized. That’s if the sterilization parameters for it are meant. Things like fractal sterilization are not true sterilization but rather types of ultra pasteurization as there is no guarantee of a hundred percent sterility a hundred percent of the time using it. When working in the field these techniques may be the best thing one can work with at the time so that’s way it's always found in many of the books on preparing mediums. But one should never confuse them with true sterilization.
We will be talking just steam sterilization now as the other types of sterilization have completely deferent sterilization parameters. What we do in the real world to find the needed time verses temperature is to run a set of test runs on what is going to be put into production. You then create a statistical model using those samplings to start with and improve on that model as more data comes in. What I use is a twenty four wire four channel thermal couple unit that takes four reading at a time multiplexed by 6 and records that data. On a basic sterilizer I will use just one but may use multiple thermal couple units depending on the size of the sterilizer chamber and the load being tested. These recordings give me the rate of how fast things are heating up at different point in the sterilizer chamber during the sterilization cycle. Since there’s a direct relationship between temperature and time; these temperature can run from 230f (used on drugs and reagents, ex. that are heat sensitive) to 270f in most cases (but for our use stay with 250 or 15psi steam pressure). The sterilization temperature is selected based on the heat tolerance of what’s being sterilized. We prove our models (the amount of time) by running a biological test (this is usually the spores of Bacillus stearotherophilus or what’s commonly called a spore test.) and the final model is always weighted toward worst case scenarios so we have a hundred percent sterility a hundred percent of the time. I hope this is of some help to you; Hipster
PS; you can make your own thermo couple thermometer from a multi meter a thermo couple adaptor and some thermo couple wire. You can find the parts online and even plans on building the adaptor. The same methodology can be used when calculating needed pasteurization temperature and times. You’re on your own now as I’ve found that things work out better if a person does their own foot work after being put the right direction!
Edited by CheeWiz (08/19/10 12:57 PM)
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jabaru
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Re: Calculating Sterilization Times [Re: CheeWiz]
#18139472 - 04/20/13 09:28 AM (11 years, 1 month ago) |
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if i sterilized my jars but i wasnt ready to inoculate them, do i have to re-sterilize them before i inoculate 4 days after the initial sterilization?
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PussyFart
Retired Cultivation Extrodinaire



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Re: Calculating Sterilization Times [Re: jabaru]
#18139593 - 04/20/13 10:16 AM (11 years, 1 month ago) |
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No
--------------------
THIS HOBBY IS NOT FOR THE IMPATIENT! PLEASE BE PATIENT, DON'T BE A PATIENT! A Tale of 10 Isolates, GT Cluster Clone Monotubs, RR's Let's Grow Mushrooms DVD, SGFC(Shotgun Fruiting Chamber), Monotub Tek, Damion5050's Coir Tek, TL's Tek List, Frank's Tek List, EvilMushroom666's Pasteurization Tek, How It Should & Shouldn't Look - NEW CULTIVATORS GUIDE *** *** AFGHAN KUSH GROW LOG *** ***
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mycofever
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Re: Calculating Sterilization Times [Re: PussyFart]
#18140861 - 04/20/13 03:59 PM (11 years, 1 month ago) |
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If your jars are sterile the contents on the inside will stay that way until you introduce spores, mycelium, mold or bacteria. I would wipe down the outside of your jars with alcohol before placing them in your glove box and before inoculating them. As soon as you pick them up and take them from the pc they will no longer be sterile on the outside.
-------------------- Patience will help you keep your sanity.It will insure your success if you are patient in all aspects of mushroom growing.When you rush you are prone to make mistakes and all of your efforts are wasted.
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jmoney757
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Re: Calculating Sterilization Times [Re: PussyFart]
#18153229 - 04/22/13 11:16 PM (11 years, 28 days ago) |
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I recently inoculated some pint jars and half pint jars but I beleive I screwewd it up already the first half I didnt let the jars cool before I inoculated so I think that basically killef that, and also gorillas the lives we lose I just tighten them down what tips would you have on how to salvage thisand im also wondering about my terrarium setup
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mycofever
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Re: Calculating Sterilization Times [Re: jmoney757]
#18153868 - 04/23/13 05:23 AM (11 years, 28 days ago) |
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Just give those jars some time the heat may not have killed your spores . It may have though. What was the rush that you couldn't wait one more hour ? I have no freaking Idea what you said in the end of your reply are you messing with us. We are getting off topic as well. We are getting into cultivation now.
-------------------- Patience will help you keep your sanity.It will insure your success if you are patient in all aspects of mushroom growing.When you rush you are prone to make mistakes and all of your efforts are wasted.
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indahighcountry
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Re: Calculating Sterilization Times [Re: mycofever]
#18163476 - 04/24/13 08:42 PM (11 years, 27 days ago) |
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this thread is odd, started as a very beginner topic but got some rather advanced answers...
anyway, what RR said trial & error will get you where you want
as a rule of thumb I'll cook qt jars at 15psi for 90 minutes and let cool INSIDE the cooker (still sealed) for 9-12 hours
remove inside the flow hood, or pull & wipe with alcohol while putting them into the glove box
make sure you give the glove box time to settle after loading & spraying when working with sterile substrate 1 bad spore can ruin a container, start figuring out how to cut corners after you have a system that works
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