The microorganisms that turn compostable coffee pods and other food and yard waste into compost at large scale facilities need oxygen – but they also need the right food in a balanced diet from those compostable waste materials.
While compost microorganisms need various micronutrients or minerals, carbon and nitrogen are the two key food requirements of composting microorganisms. Carbon is contained in the molecules that make up the twigs, dry plant materials and coffee pods that we want to compost. We can find more nitrogen in fresher materials such as green leaves, grass clippings, and the remains of fresh vegetables.
Where does coffee fit? It has a relatively high nitrogen content so composters see coffee grounds as a plus for feeding the microorganisms that do the work in their composting operations.
Just like in our own diet, microorganisms need the right balance of nutrients for good health. Compost microorganisms thrive when the carbon to nitrogen ratio is roughly between 25 to 1 and 35 to 1. In other words, carbon is the primary food for the microorganisms and it provides the energy they need. But they also need some nitrogen to create their protein building blocks.
It all about balance. Too little nitrogen and the compost process will proceed very slowly, if at all. Too much nitrogen and the microorganisms will die, likely resulting in the compost pile being taken over by the anaerobic microorganisms that lead to a very smelly pile.
Operators of compost facilities know all this and they test the ratio between carbon and nitrogen regularly. When they see a little too much nitrogen in the compost pile, they will mix in more dry material, such as wood chips or paper – all often called “browns” by home composters, to push up the pile’s carbon content. If there is too little nitrogen then food waste, grass clippings, or animal waste and other “greens” can be used to increase the nitrogen content.
Want more detailed information about carbon to nitrogen ratios in composting? Try these sources: