In its simplest form, healthy compost is a collection of organic, compostable materials that have been mixed together, and is in the process of decomposing. Your compost pile is healthy if it is decomposing the materials that you put into it. Optimum composting health is occurring, if your compost pile is decomposing at a maximum rate, producing finished compost, under ideal conditions, in as little as 14 days!
Compost health can be measured in the speed at which it takes the materials to decompose. From start to finish, a batch of compost can be made from 14 days to 2 years. A compost pile that is not decomposing, or is decomposing ever so slowly, is not healthy.
Another example of a compost pile that is not healthy, is when composting grass clippings. Mow the lawn and bag it. Pile the grass clipping up into a pile. Come back just a day or two later, and you find a slimy, gooey pile, that is giving off an obnoxious ammonia odor. By all means, this is an unhealthy compost pile. However, by mixing in ample amounts of brown materials with the grass, you avoid this mess.
You can maximize the health of your compost pile by paying attention to composting basics: