For the active composter there are a few key parts of the composting process that they will need to keep an eye in order to help the compost along in the most efficient way. What exactly those parts are can be a subject of much heated discussion but in general most people that deal with compost agree on the following four.
Having these four key of composting in sync can lead to producing quality compost in a efficient and predictable manner. For anyone that needs or wants compost on a larger scale it is vitally important to fully understand what the four elements of composting above can do to your pile if they are not managed correctly.
Finally we have come to the last key of active composting that I will be covering in my four part active composting series. The type of composting that is ideal for the backyard is aerobic composting. Aerobic composting produces the black gold that people imagine when they think compost and it does it quickly and with little smell when done correctly. The air around us is around 21% oxygen and the microorganisms in your pile need this oxygen to operate effectively. Now they will be able to do this till around 10% available oxygen in the pile. Below 10% and you will start to get “dead” spots in your pile that will start composting anaerobically and that produces hydrogen sulfide gas which is the rotten egg smell that turns a lot of people off of composting. Most of the time a pile can maintain sufficient oxygen levels through natural convection and diffusion through the piles materials. If you look to the diagram on the right you can see how convection pulls cool air into the bottom of the pile as hot air moves out the top. As the compost progress the pores that allow this natural oxygen flow to occur can become smaller or even closed and it may become necessary to physically turn the pile over to add oxygen. If maintaining oxygen in your pile is a consistent concern you can also use a perforated PVC pipes stuck into the pile which will provide a channel for air to get into the pile. Some people will also build a pile around some dead brush that keeps the pile loose and aerated but the heavy woody materials can make it difficult to turn the pile over.
With a correctly designed pile it will maintain oxygen levels on its own but as with many things in life it doesn't always work how it is suppose to. Like with the other keys keeping an eye on this one will greatly help you in your quest for the black gold that is compost.
One last bit of advice I can offer on the science/art of composting is that you just have to get out and do it to really learn how to create compost effectively. You can read a hundred articles and have all the books but until you take the time to get your hands dirty you wont really "KNOW" how to do it. With that in mind I want to wish all you brand new composters good luck and happy composting.