According to Cornell University, there are three main stages in the composting cycle in which different types of microorganisms thrive.

The first stage is typically only a couple of days long during which mesophilic microorganisms, or microorganisms that thrive in temperatures of about 68 to 113 degrees Fahrenheit (20 to 45 degrees Celsius), begin physically breaking down the biodegradable compounds. Heat is a natural byproduct of this initial process and temperatures quickly rise to over 104 degrees F (40 degrees C).

Mesophilic microorganisms are replaced by thermophilic microorganisms (microorganisms that thrive in the increased temperatures) during the second stage, which can last from a few days to several months. The thermophilic microbes work to break down the organic materials into finer pieces. The higher temperatures are more conducive to breaking down proteins, fats and complex carbohydrates.

Also, during the second stage, temperatures continue to rise and if not closely watched, the compost pile can get so hot that it can eventually kill off all the helpful microorganisms. Techniques such as aeration and turning over the compost pile help keep temperatures below about 149 degrees F (65 degrees C), as well as provide additional oxygen and new sources for the thermophilic microorganisms to break down.