Organic Gardener's Composting by Steve Solomon

The main difference between composting in heaps and natural decomposition on the earth's surface is temperature. On the forest floor, leaves leisurely decay and the primary agents of decomposition are soil animals. Bacteria and other microorganisms are secondary. In a compost pile the opposite occurs: we substitute a violent fermentation by microorganisms such as bacteria and fungi. Soil animals are secondary and come into play only after the microbes have had their hour.

Under decent conditions, with a relatively unlimited food supply, bacteria, yeasts, and fungi can double their numbers every twenty to thirty minutes, increasing geometrically: 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1,024, 2,048, 4,096, etc. In only four hours one cell multiplies to over four thousand. In three more hours there will be two million.

For food, they consume the compost heap. Almost all oxygen-breathing organisms make energy by "burning" some form of organic matter as fuel much like gasoline powers an automobile. This cellular burning does not happen violently with flame and light. Living things use enzymes to break complex organic molecules down into simpler ones like sugar (and others) and then enzymatically unite these with oxygen. But as gentle as enzymatic combustion may seem, it still is burning. Microbes can "burn" starches, cellulose, lignin, proteins, and fats, as well as sugars.