A couple of days ago I took our compost thermometer out to see how hot the pile was. Here was the result.
Any pile of organic matter will eventually decompose if left long enough. But, it is best to build your compost pile in such a way as to produce aerobic decomposition. This method produces heat, and heat is beneficial in order to kill pathogens and weed seeds that lurk in the organic material. Ideally, you want your compost to reach 140 degrees. As you can see above, we are well above that!
In order to produce this much heat, you want to have both carbon and nitrogen organic materials. The optimum ration is 25 or 30 parts carbon to 1 part nitrogen. But, we don't worry about the ratio that much. Examples of carbon sources are leaves, wood chips, and sawdust. Examples of nitrogen sources include grass, food waste, and manure. These materials are decomposed by organisms utilizing oxygen, thus the name "aerobic".
The heat being produced is evident when the pile is turned. Here is a picture of Tom turning it with our tractor. Note the steam being emitted.