Blending waste materials to balance these nutrients results in faster composting with less potential for odor problems. Microorganisms need water to maintain their metabolic activity. It should feel damp to the touch, expelling just a drop or two of liquid when tightly squeezed in the hand. Composting is an aerobic process, which means it occurs in the presence of oxygen. When a pile receives too little oxygen, parts of it become anaerobic, and offensive odors can result.
Oxygen moves into the pile primarily by diffusion.
If a pile is too large, not enough oxygen can get to the center. Forced aeration is sometimes used to supply oxygen in large compost piles. An oxygen analyzer is useful for determining the aerobic quality of the compost. As organisms decompose waste, they generate heat. Overheating results in drastic population fluctuations and possibly unpleasant odors, as the pile sterililzes itslf and microorganisms die.