At its simplest level, composting requires gathering a mix of 'Greens' and 'Browns'. Greens are materials rich in nitrogen such as leaves, grass, and food scraps. Browns are more woody materials rich in carbon-like stalks, paper, and wood chips. The materials are wetted to break them down into humus, a process that occurs over a period of months. Most organic standards demand at least a 60 days composting process, however, composting can also take place as a multi-step, closely monitored process with measured inputs of water, air, and carbon- and nitrogen-rich materials. The decomposition process is aided by shredding the plant matter, adding water, and ensuring proper aeration by regularly turning the mixture when open piles or "windrows" are used. Fungi, earthworms and other detritivores further break up the organic material. Aerobic bacteria and fungi manage the chemical process by converting the inputs into heat, carbon dioxide, and ammonium.