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Offlineblackout
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thermal death times of various grains at various temps
    #1316026 - 02/18/03 07:11 AM (14 years, 2 months ago)

anybody know the TDT of millet or rye (or any other common substrates) at say 70,80,90 and 100C


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Re: thermal death times of various grains at various temps [Re: blackout]
    #1316041 - 02/18/03 07:20 AM (14 years, 2 months ago)

Why are you concerned with keeping your grain alive? If you are using it for cultivation, you don't want the seeds to sprout.


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Re: thermal death times of various grains at various temps [Re: Joshua]
    #1317326 - 02/18/03 05:27 PM (14 years, 2 months ago)

I think what he means is At what temps do the sugars in the grains carmalize rendering them useless as spawn I heard that this could happen if you pc for too long or at too high a temp ther is a reference to this in The TMC by paul stamets


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Re: thermal death times of various grains at various temps [Re: Joshua]
    #1317853 - 02/18/03 10:29 PM (14 years, 2 months ago)

i want to know the minimum time the grain must be kept at say 100c to be sure they are sterile. i have read that some bacteria it is 800mins at 100C. i want to ensure it is killed i'm not keeping it alive


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Edited by blackout (02/18/03 10:30 PM)


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Re: thermal death times of various grains at various temps [Re: blackout]
    #1317906 - 02/18/03 11:32 PM (14 years, 2 months ago)

so you're asking the thermal death time for contaminants present in various grains?
if so, the answer is complicated. it depends upon [all] the contams present to begin with, wich you really cant find out for sure.
it is established that just about anything you will find living in most grain will be killed by PCing for 60 min at 15 psi. you could go longer, but you don't want to overdo it, as over-cooked gain [rye for example] can be more prone to contamiation than that PC'd at normal duration and pressure.

hope that is what you where looking for.


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Re: thermal death times of various grains at various temps [Re: canid]
    #1318090 - 02/19/03 02:53 AM (14 years, 2 months ago)

"so you're asking the thermal death time for contaminants present in various grains?" yep
"if so, the answer is complicated." it always is!
i was reading a microbiology textbook and it was talking about how important TDTs are for the food canning industry. they do not want to heat to high temps since the food will taste bad. so they have to find the right temperature and time that doesnt affect taste too much. if the temp used is very low the TDT is huge so it may taste even worse than after heating high for a short time.
just wondering if anybody has a canning industry guide to TDTs for various products.
i remember reading a freezer industry guides to temperatures needed for freezing various foods. it had a huge amount of info on just carrots. broken down into small carrots, cooked carrots, carrots in brine, carrots in water, ready cooked carrots.
there must be similar guides for canning.

its just that i know of a place i can put jars that will be at 90C+ for weeks at a time


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Re: thermal death times of various grains at various temps [Re: blackout]
    #1318422 - 02/19/03 07:00 AM (14 years, 2 months ago)

the TDT does not applie to the substrate, it applies to whatever microbes are present in the substrate, at the temperature you want to use.
what you seem to be asking is the maximum sterilization temp for the given substrate. that's not the same as the TDT (a ratio of temp over time).
one reason you don't want to heat grains too high is that the majority of the nutritional value is from carbs. carbs are sugars, and will caramelize if the temps get too high. i'm not sure what the breakdown points are for different carbs, but i immagine they are not too far from that of refined sugar.

as you read this you're probably muttering "no shit dumbass", so forgive me if i'm not helping, i'll check some homebrewing resources and see if i can find anything specific.


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Re: thermal death times of various grains at various temps [Re: canid]
    #1320703 - 02/19/03 11:43 PM (14 years, 2 months ago)

"the TDT does not applie to the substrate, it applies to whatever microbes are present in the substrate"

-this microbiology book inferred that there would be different values for different foods/substrates. i presumed that they would know what average types of microbes are in each food type and how long it would take to kill them. so yes, the TDT will be different for each microbe so you need to know all the microbes present. it said the way they determine the TDT was that they held a stock culture of food at a set temperature and kept taking out samples at various time intervals and when the samples showed no grow growth in a broth/agar then this was the minimum time needed to kill all the microbes present.

"what you seem to be asking is the maximum sterilization temp for the given substrate."

-no, i'm asking for the minimum sterilization time for a given substrate at set temperature. as the set temp increases the minimum time required will get shorter. like at 10psi it will take longer to sterilise than at 15psi.

i have seen it mentioned on some brewing sites, one mentioned about 850mins for a particular wort at 100C


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Re: thermal death times of various grains at various temps [Re: blackout]
    #1320711 - 02/19/03 11:54 PM (14 years, 2 months ago)

heres another question for the experts.

fractional sterilization from the FAQS is as follows

Timetable of the tyndallization (=fractional sterilisation) process

1) Steam heating to 100 ?C for 30 min
Vegetative cells are destroyed but endospores survive

2) Incubate at 30?C-37?C overnight
Most bacterial endospores germinate

3) Second heat treatment, 100 ?C, 30 min
Germinated spores are killed

4) Second incubation at 30?C-37 ?C overnight
Remaining endospores germinate

5) Third heat treatment, 100 ?C, 60 min
Last remaining germinated endospores are killed

this process takes about 3 days.
what if i just heated to 100C for 3 days would this be even better or do the endospores have to get down to 30C to germinate?


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Re: thermal death times of various grains at various temps [Re: blackout]
    #1320745 - 02/20/03 12:48 AM (14 years, 2 months ago)

This is the case, yes.


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Re: thermal death times of various grains at various temps [Re: blackout]
    #1322039 - 02/20/03 12:18 PM (14 years, 2 months ago)

i say, experiment and decide for yourself, just use innoculation from a stock culture, you'll know you evercooked it if the growth rate seems overly clos, or much less viggorous than normal. however, if i happen upon anything opertainent, i'll post it.
good luck.


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Re: thermal death times of various grains at various temps [Re: canid]
    #5190334 - 01/17/06 10:43 AM (11 years, 3 months ago)

3 years on and I am still searching for a table of these TDT's! Anybody know? or point me to another website with a forum on microbiology?

I found this on a homebrew page. They would be cooking grains similar to what we use.

Quote:

While sterility may seem like an impossible ideal, it is a goal that can be reached. The two main factors are temperature and exposure time. A guy named Bigelow once studied this topic, and came up with the idea of Thermal Death Time, the shortest period of time required to kill a known microorganism at a specific time. He then went about calculating various TDT's. What he found is at 100C (Chip-I don't know about you, but my water boils at this temp (although I realize altitude and [sugar] will affect this, but usually lowering it)), it takes 788 to 834 minutes (average) to insure destruction of 15 typical thermophiles.



http://www.hbd.org/hbd/archive/886.html


another

Quote:

The complete sterilization of a vegetable required that one heat the vegetable in the jar to the boiling point of water and maintain that temperature for one hour each of two or three successive days. The first day of boiling was to kill molds and almost all the bacteria, but not spores. The spores were thought to germinate upon cooling, and boiling the second and third days killed the new bacteria. If fractional sterilization were not practiced, about five hours of boiling on the first day was recommended.



http://www.fcs.uga.edu/pubs/current/earlyhis.htm


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Edited by blackout (01/17/06 11:11 AM)


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Re: thermal death times of various grains at various temps [Re: blackout]
    #5190571 - 01/17/06 12:34 PM (11 years, 3 months ago)

Complete sterilization is not necessary and would render the grains unusable for mycelium. 90 Minutes at 15 psi is a good compromise that gives a two to three week window of opportunity for the mushroom mycelium to colonize the grains before contaminants have a chance to re-emerge. Bacterial endospores are what we are trying to slow down enough to allow our grains to colonize. Molds such as trichoderma are killed off by much lower temperatures.
RR


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Re: thermal death times of various grains at various temps [Re: RogerRabbit]
    #5193970 - 01/18/06 04:46 AM (11 years, 3 months ago)

Quote:

RogerRabbit said:
Complete sterilization is not necessary and would render the grains unusable for mycelium.



So do you think that heating at 97C or 100C can give the same "acceptable sterilization" that 90min 15psi can?

I have access to a boiler that is constantly at 97C. I will try a jar or grain and see. I have already done a manure/pasta mix in a 4.5litre glass jar for 28hrs in it.

I do not understand why completely sterile grains are unusable for myc...


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Re: thermal death times of various grains at various temps [Re: blackout]
    #5201800 - 01/20/06 08:40 AM (11 years, 3 months ago)

Well I am going to try about 100g of barley at 99C for 48hrs and see how I get on.


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Re: thermal death times of various grains at various temps [Re: blackout]
    #11247215 - 10/14/09 06:26 PM (7 years, 6 months ago)

Quote:

blackout said:
Well I am going to try about 100g of barley at 99C for 48hrs and see how I get on.



I cannot remember what happened to that jar, I have found several jars a few years old which are still showing no signs of contams, some were microwaved others I cannot remember. I am currently heating grains in water at ~98C for a planned ~14hours. 4 jars with 110g of oat & wheat grains.

I found a site listing the TDT of Clostridium botulinum at 5-5.5hours. And I found another site which comments on fractional sterilization which I have had success with, though different to the textbook recommendations

Quote:

Her experiments with 10 strains of C. botulinum involved heating suspensions of free spores at various temperatures and pressures for different periods of time. Conclusions from her studies include:

  1. Spores of C. botulinum will survive boiling for 3½ hours or more; therefore, kettle canning cannot be relied on to sterilize material contaminated with spores of C. botulinum.
  2. The one-period cold-pack process was not sufficient to kill spores of C. botulinum. Blanching in boiling water for 5 minutes did not destroy spores. Heating in boiling water for 5 hours or less would not sterilize food contaminated with C. botulinum.
  3. Fractional sterilization on three successive days was of doubtful value because the initial exposure to 100C for 15 to 60 minutes delayed the germination of the spores until after the third sterilization period.
  4. Pressure canning was the only method of sterilization considered safe; however, a pressure of 5, 10 or 15 psig for 10 minutes was not sufficient.




http://www.uga.edu/nchfp/publications/usda/review/earlyhis.htm


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