Composting can be defined as the controlled biological decomposition of organic materials under aerobic and thermophilic conditions. Composting is a controlled process, like any other manufactured product. It is also an aerobic process in that the organic materials decompose in the presence of air. Composting is a thermophilic process, meaning that it takes place at temperatures above 45°C for extended periods during processing. Thermophilic composting is desirable for a few reasons – faster decomposition speeds up the composting process and helps to eliminate pathogens and weed seeds that might be present in the raw material. Composting transforms organic materials into a safe, reusable product called compost.

Process control is the distinguishing feature of composting because it enables operators to meet their biosecurity and environmental management goals and obligations. In this guideline, process control is emphasised because the term ‘compost’ has often been wrongly attributed to many different types of organic materials derived from uncontrolled processes. For example, poultry litter that self-heats in a stack without further management controls cannot be called compost.

In poultry operations, a major factor to consider is the predominant raw materials (‘feedstock’) to be composted. For example, due to biosecurity risk factors, mortalities must be handled differently compared to other feedstock.

With a basic understanding of the biology of composting, operators will be better placed to exert control over the process. The biology of composting will therefore be covered briefly in the next section.