Compost temps higher than 160F

josko021July 19, 2010

I've been learning to compost fish scrap together with suitable browns, and have got to the point where there is no noticable outgassing or undesirable odors. However, temps in a pile typically soar to more than 160F within a few days.

For instance I just made a pile with 300+ lbs of fish scrap and about 2 cubic yards of finely-chipped ramial chips. The 4'x4'x5' pile measured 171F abot 18' from the top three days after i set it up. I deliberately left it a bit on the dry side, and am pretty confident that chip size is large enough to allow aerobic decomposition.

Trouble is, I read that thermoplilic bacteria die off at 160F, so I'm wondering what's going on to maintain such a high temperature. Typically, 160+F temps will last for about a week before slowly tapering off.

Is this due to overenthusiastic thermophilic bacteria, or is ther eanother decomposition process that takes over at 160F?

Also, should I be concerned about all these wood chips catching on fire?

The link below is a thread with some details of my learning process.

Thanks in advance.

Here is a link that might be useful: composting fish scrap

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I haven't gotten anything over 165 myself and even then that is in isolated pockets in the windrows.

From what I've read,some of the thermophiles begin to die off at 160. Wiki says the range is up to 176 and after that it's the "extreme" thermophiles. Those guys must be some kind of bad a$$ bacteria!


    Bookmark   July 19, 2010 at 7:36PM
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Thermophiles may die at a certain temp, but they survive at the fringes and beyond the nuclear temperature core of your compost. You basically got one smokin compost pile and it's gonna be seriously rich good stuff when it's done. You can slow it's roll a bit by adding more browns. By the way congrats on reaching the stratosphere of compost temps! You're like the Tesla of compost!! LOL

    Bookmark   July 19, 2010 at 9:01PM
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There are many different thermophilic bacteria that are at work, not just one species and each functions at different temperatures. The problem is not so much that some of the thermophilic bacteria might die off at temperatures above 160 degrees but that sopontaneous combustion is possible when temperatures of piles of organic matter get that high.
Frank Teuton, some years ago, wrote a very good treatise here about thermophilic bacteria. It may still be here.

    Bookmark   July 20, 2010 at 6:38AM
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I make the 160s pretty regularly with shredded stable bedding, leaves, and grass clippings. What I find is that the heat drives out the moisture so I have to turn and re-hydrate the piles often. The result is quick compost but lots of work.

I turned my two main piles yesterday sprinkling with the hose as I moved them one pitch fork at a time. I was surprised to see the thermometer reading above 150 degrees this morning.

The fresh stable bedding (no grass clippings yet) that I shredded yesterday are at 135 degrees now so that stuff came to life really fast. It was urine soaked bedding so I guess the nitrogen levels are high. Can't wait to see what happens to that pile when I toss in some fresh clippings when I next mow! I'll probably be roasting hot dogs over it. ;)

    Bookmark   July 20, 2010 at 12:36PM
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I have a chipper that can chip branches up to 3" dia. When I chip freshly cut green branches and pile up the chips, the pile gets very hot, very quickly. I seem to recall temps in that range, but my memory is fuzzy.

Next time I chip up some ramial wood, it's going straight into the soil instead of being put into a compost pile. I'll be enlarging some beds this fall, so I'll be doing it then.

    Bookmark   July 23, 2010 at 11:10PM
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So what's the ideal temperature of a 'hot' pile? Mine's been running above 165 for a week now, but it's not at all smelly, seems to have settled a good 8"-10", and all seems well, although it hit a high of 175. I'm pretty sure I can get peak temps to drop by mixing in more wood chips, but am unsure what temperature to try to shoot for.
Other than the risk of fire, is there a downside of letting a pile get that hot?

    Bookmark   July 24, 2010 at 7:05AM
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175 Wow! I've never had a pile get quite that hot. I would guess the danger of that kind of heat is that the microbes might start being killed off.

I like to turn my piles often to mix and keep the hydration right. I think turning brings down the temps a bit and puts new "fuel" into the core of the furnace.

    Bookmark   July 24, 2010 at 9:13AM
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When I had two compost thermometers, I found there was a difference of 10F or more. My best core temp was 165F with the bin size of 4' round and 2' high.

    Bookmark   July 24, 2010 at 3:35PM
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pkapeckopickldpepprz(z9 a/b FL)

175!!! Man you deserve a medal for that temp!

    Bookmark   August 2, 2010 at 12:08AM
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Most everyone that haws studied composting will tell you that you should be turning and remixing your compost pile when the core temperature reaches about 145 degrees.
The link below may be of some help.

Here is a link that might be useful: Composting Tutorial

    Bookmark   August 2, 2010 at 6:51AM
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Well, yes, in principle, I agree. However, these piles contain a considerable amount of animal matter carefully layered with browns, and I don't want to risk bringing that stuff to the top or to the bin side, because of the risk of odors and putrefaction.
Instead, I've been trying to increase the brown:green ratio and making sure the piles are well wetted. My principal concern is spontaneous combustion, since the piles are not outgassing anything smelly, and the end product seems fine.
I just turned a pile started in early June, and ammonia smell from the center of the pile is still strong. Until I turnwed it, I couldn't smell anything, although it had cooled to 110F.
So until I learn a downside of leaving it alone and wetting it, I'm tempted to just leave these piles be until they cool down, maybe with a few more wood chips in the mix. I'd appreciate hearing about the downside of not turning - maybe there's an issue I've neglected.

FWIW, I tested my 20" compost thermometer in boiling water, and it read ~215, so it is a few degrees high, but not significantly.

    Bookmark   August 2, 2010 at 11:36AM
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pkapeckopickldpepprz(z9 a/b FL)

Ironic kimmsr is posting a composting tutorial to someone who I would regard as one of the best composters to attain such a high temperature. Josko, I think what you are doing is working as you are minimizing odor while maintaining super high temps. You shall be crowned master composter!

    Bookmark   August 2, 2010 at 9:49PM
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The ratio of vegetative waste to manure should be 3 to 1, or as Sir Albert Howard and many others since have found 6 inches of vegetative waste to 2 inches of manure. A lower ratio can result in higher temperatures and higher temperatures get very close to the potential of spontaneous combustion, whihc is why many people that do compost do not consider temperatures in the 160 degree range good.

    Bookmark   August 3, 2010 at 7:27AM
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Whoa, folks, my 10 4x4' compost bins to date do not an expert make. I think we'll all agree that burning down the yard for a palletbin of compost is not a good trade.
So far, I've learned to mix in fish scrap and finely-chipped (ramial) brush to almost completely stop undesirable outgassing and produce decent-looking compost.
But it seems we have a concensus that letting it get above 160F is a bad idea, certainly from a safety standpoint, and also possibly from a chemical point of view, although I really haven't found a reference for or evidence of deletorious chemical processes in >160F compost piles.
It's intuitive that increasing the chips:fish ratio should cool the pile, but sice fish scrap is easier for me to get than brush chips (which I got to chip with my little Mccullogh electric chipper) the temptation is to use the least brush possible. I've been using shredded office paper as a brown as well, with good effect.
I've been very appreciative of all the composting links provided on this forum, particularly the Cornell website and their on-farm composting handbook (link below). Please keep the advice coming. I do appreciate it.

Here is a link that might be useful: on-farm composting handbook

    Bookmark   August 3, 2010 at 8:53AM
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I think you're doing great. I look at my high composting temps with pride. I also use a lot of fish but not in the piles. I dig 10 to 12 inch deep holes directly in the garden and dump the bait fish (3"- 4" shiners) right in and re-cover with dirt. They degrade so fast that I can repeat the process in the same spot in a month or less and not dig up any rotting fish. SW Florida here so maybe the subtropical heat helps?

    Bookmark   August 6, 2010 at 4:41PM
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Has anyone got any hard data on spontaneous combustion in compost piles? 160 degrees F seems far too low to be even remotely worried about combustion. You'd need to be somewhere over 400F for cellulose, lignin, or other common compost materials to burn. Is there something I'm missing?

Here is a link that might be useful: Auto-ignition temps of selected fuels

    Bookmark   August 6, 2010 at 5:13PM
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I've not seen anything where someone deliberatly tried to make a compost pile self ignite although both the National Fire Protection Association and the people at the Forest Products research lab have done this with sawdust, bark, and other similar material. Research has not been done on improperly cured hay spontaneously combusting either but most evey rural firefighter has been to a barn fire caused by that as well as many of us being at a fire caused by spontaneous combustion of a compost pile.

    Bookmark   August 7, 2010 at 7:57AM
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Josko, there are two booklets on composting only fish products. Have you read them? I'll find the names and authors if you are interested.

    Bookmark   August 7, 2010 at 3:23PM
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I am a retired fire captain and in 35 years I never heard of compost pile causing a fire. Large MULCH piles of freshly chipped materials can and do ignite spontaneously, as can oily rags. A home compost pile lacks sufficient oxygen and has too much moisture to be considered a fire hazard, IMO.

    Bookmark   August 7, 2010 at 4:42PM
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"Research has not been done on improperly cured hay spontaneously combusting either..."


Much research and study has been done on this.


Here is a link that might be useful: Hay Fires: Prevention and Control

    Bookmark   August 7, 2010 at 5:02PM
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Robert, I'd love to get a reference to those fish-composting booklets you mention.

    Bookmark   August 8, 2010 at 8:56AM
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josko, I would love to know what you & captturbo have learned in the last 7 months , about fish composting. How about a up date.
captturbo, have you ever seen muck- horse straw/hay & manure- smoke when in a pile(not compost pile), just dumped out of a cart. I have saw this at a stable, I ask the stable hand does it flame up(combust, he said not in the three year he had worked there. Even then many OG came to get the older,4-5 weeks, piles for their compost piles.
We always left the hay in the field for at least 3 days, even if rain was in the forecast.

    Bookmark   January 9, 2011 at 9:52PM
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Well, I've learned to make compost (in a pallet bin) consisting of up to 400 lbs of fish or fish scrap and a couple cubic yards of finely-ground woodchips mixed in with shredded paper. I stockpile woodchips, paper and pallets for the times when I can get a lot of fish scrap. This ranges from herring to dogfish to striper/bluefish racks and is the stuff I used to use for lobster bait, so I've learned to scrounge for it.
If I don't have a full 400 lbs, I'll freeze fish in ~60 lb 'totes' so I can build the whole pile at once.
Construction is pretty straightforward: wire together 4 pallets (I tend to look for large ones) and put down a couple of inches of brush. Then layer 3-4" of woodchips and a tote of fish, taking care the fish doesn't get within 6" of a side. If possible, mix woodchips or paper with each tote's contents. Keep layering until 6-8 totes are used up. Wet each layer down copiously. This ends up with a ~4' tall pile. At the top stick on a 4"-6" layer of woodchips, and then wire another pallet on top. I have shepeherds that discourage other animals, so animal scrounging hasn't been a problem.
Somewhat surprisingly, the piles don't smell, or if they do, they'll give off a faint ammonia odor after about a week. I was very nervous about putrid odors, but now think that layering and mixing each tote with shredded paper or wood chips help in this aspect.
Such a pile will typically go to or even above 160F for up to three weeks and then slowly subside. During the first month height will drop by about 1' or more. Trying to turn it at this stage exposes VERY strong ammonia smell - it can be overwhelming; so I've learned to leave it alone for 3-4 months. When opening it at this stage, sometimes there are dry pockets of undecomposed wood chips, but overall, most of it will sift through 1/4" hardware cloth.
I use the compost on my lawn, and sift it through 1/4" before topdressing, or on the veggie garden, where I do't bother sifting. In 2010 I made 8-9 pallet bins, and they all worked out great. (I made one with ~500 lbs of starfish instead of fish scrap.) I haven't had my compost tested, but it looks and smells very nice. Right now I have 4 bins maturing, ready to go on when the ground is ready to spade.
Overall, it worked very well. I suppose I should have the compost tested, to make sure I'm not unbalancing the soil over the long term.
I'd be glad to answer any specific questions.

    Bookmark   January 10, 2011 at 10:24AM
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Unbalancing can be a problem, when you use the same ingredients over & over, like the tons of coffee waste I have. I am going to add gypsum, azomite, Biochar & do a soil test after cutting the finished compost in to the raised beds. This may or may not be the best way ,but it is what I am doing.
Thank you for the up date.

    Bookmark   January 10, 2011 at 12:33PM
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When I was a boy and we had a farm running with lots of horses, some cattle, sheep, and pigs, I had to keep the piles of stable litter away from the barn siding. We would toss it out the windows and it would mound up against the barn. Yes, these piles would start smoking pretty quickly but the fear wasn't that they would ignite. The worry was that this stuff was so biologically hot it would begin to compost the barn siding. So, I had to pull the tractor cart or the manure spreader up to the piles and I always started at the part that was in contact with the barn. The wood would be wet and hot from the composting manures.

As to my experince with dumping all those bait fish and fish carcasses into holes in my garden. I'm glad that I did it but I will do it differently for the next go-round. I put too much in each hole this time. As I was setting in my plants I found spots where there was a good bit of bones and scales that were not completely broken down. I don't think there was enough air getting to it the way I just piled in five gallon buckets and covered it all.

The next attempt will be done by digging trenches and pouring in the fish in a more spread out area where there will be more fish / soil contact. Hope this makes sense to you.

    Bookmark   January 12, 2011 at 12:00PM
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