Microorganasims drive this process and are composed of bacteria, actinomycetes and fungi. Bacteria are composed of three different types that work best and different temperature ranges. Psychrophilic bacteria start the composting process and prefer the lowest temperature range and are most active at 55 degrees F. Their activity produces a small amount of heat so that the mesophilic bacteria can take over. Mesophilic bacteria prefer a temperature within the pile of 70 to 100 degrees. They are followed by the most heat-loving bacteria which are the thermophilic bacteria. They thrive at temperatures between 113 to 160 degrees F. These microorganisms die when they finish digesting the material in the pile and the temperature drops.
Actinomycetes are a special bacteria that are similar to fungi and molds. They are important as they help decompose some of the more resistant materials such as lignin and cellulose. They work best at moderate temperatures.
Fungi are less heat resistant and prefer temperatures between 70 and 75 degrees F. They are compost “finishers” and are most active after the other microorganisms are done.
So the compost pile goes through a process whereby the compost pile starts cool, builds up to a high temperature and then cools. Next week we will look at what we need to make a compost pile. For more information on compost pile microbes, see https://www.calrecycle.ca.gov/organics/homecompost/microbes (Ward Upham)