this post was submitted on 12 Nov 2023
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@hamtron5000
This temperature target is really just to begin killing weed seeds - it takes a sustained temp above 140F/60C to begin killing pathogenic bacteria, with ~160F/71C being required to get to the most tenacious. If all that's being composted is grass and garden waste and leaves and wood chips then by all means aim for 120F/49C but if the pile incorporates manures or carcasses then 160F/71C should be the target temperature.
Pathogen destruction is a function of time and temperature. Generally speaking, a compost bin at 140F/60C for an hour will kill most pathogens, or 130F/55C for a day, or 120F/49C for a week. And generally, compost bins will hold a peak temperature for between 24-72 hours before slowly dropping again, while adding fresh material will make the temperature rise again. Part of the reason time matters is because it isn't just heat that kills pathogens - it's also compost microorganisms that physically kill pathogens in the bin.
Getting compost very hot like 160F/71C like you say will kill pathogens quickly but it's not only unnecessary, it's also harmful, as a lower temperature will result in a more diverse culture of bacteria in the finished compost. Personally I aim for about 140F/60C.
And anyway, note that I said above 120F. It sounded like the GP was having issues with their compost that made me think that 120F would be a reasonable target to shoot for given their current situation.
These are very good points, and I hope you understand that my comment was coming from a place of care for a novice composter in the same vein as yours. My experience teaching new composters has caused me to give the 140-160F targets as that's the most likely way for their pile to reach the minimum temperatures for these processes to play out.