"What am I looking for when I take my compost pile temperatures?"

1. Our primary goal is for your compost to reach and exceed 131°F for at least three days. This is referred to as a "Process to Further Reduce Pathogens" or PFRP.
   
   
2. The rate at which the pile temperatures change during the first week to 10 days of active composting is equally important as achieving the PFRP. High energy feedstocks (e.g. chicken manure) will rise very quickly whereas low energy feedstocks (e.g. alpaca manure) will rise more slowly.
   
   
3. When building a pile with daily additions of manure and stall bedding, the pile will already begin to build heat in its core before turning on the airflow. With aeration, the pile temperature is expected to increase 20 to 30 degrees in 12 to 24 hours. If it doesn't, something is wrong and we need to do some troubleshooting.
   
   
4. Read the following and then immediately forget that I said it:  From a biological standpoint, the optimum pile temperature is between 100º and 120ºF. Within this temperature range, we have the greatest number and diversity of bacteria doing the composting work for us and the rate of composting is optimized.
   
   
5. "Too hot" is when core pile temperatures exceed 165-170ºF. At these higher temperatures, the biologic process becomes less efficient and the pile is prone to release odorous gases (i.e. volatile organic compounds).
   
   
6. If the pile temperature gets too high, we want to increase the airflow into the pile as a way of "mechanically" displacing the heat out of the pile, replacing it with ambient air. Reducing the pile temperature does not happen quickly and may take a day or two.
   
   
7. Increasing the airflow to cool the pile down will also dry the pile out. If the pile moisture content drops much below 50%, the composting process stops. This is particularly true during the winter months when ambient air is cold and very dry.
   
   
8. For this reason, I prefer a pile that runs a bit too hot (biologically less efficient) to one that becomes dry. This is why I'm asking you to forget #4 above. 
   
   
9. If the core pile temperature drops precipitously (over a day or two), your mix has likely become too dry. If this happens, the only option is to remix and remoisten the compost.
   
   
10. Pile temperatures after four weeks become less relevant. For example, large curing piles can stay warm for months because compost is self-insulating and the pile is retaining heat, not generating heat.
    
    
11. Pile temperatures can vary greatly depending on where you insert the temperature probe. Don't worry about aberrant temperature readings from day to day.
    
    
12. It is important to take temperature readings for the first few batches so that you understand the cause and effect of managing airflow into the pile. However, you have my permission to relax your monitoring efforts after you have become comfortable with the process.