This is a huge and fascinating topic and there are numerous books, articles and websites available for you to lose yourself in! However, Peter Harper at the Centre for Alternative Technologies in Powys came up with this rather tasty summary (2001). Note that it refers primarily to garden waste and favours cool composting.
If you intend to take up the challenge and compost your own household waste it is handy to understand some of the principles that make composting work. To make things easier for beginners, we have introduced a new terminology based rather whimsically on bread and cheese.
The creation of a tasty bread-and-cheese sandwich is an excellent guide to what will and will not work in composting. Both practices, sandwich-making and compost-making, work best when they draw on the complementary qualities of light, open-textured, carbohydrate materials and dense, moist, protein-rich materials. If you are ever in doubt about what to do in composting, ask yourself this: what makes a good cheese sandwich?
Firstly the proportions of bread and cheese need to be right. Too much bread is dry and tasteless. Too much cheese is equally unpleasant in a different way. Equal volumes is roughly right, although it is usually better to have somewhat more bread. But it works well within quite a broad range: there’s no need to be too fussy.
Secondly the ingredients need to be combined in the right way. A block of bread and a block of cheese eaten one after the other is no good, even if the proportions are right. Neither is putting the ingredients in a blender and eating the resulting baby food. They need to be combined fairly intimately while still retaining their identity, and thin layers of each is a very effective way to achieve this.
Thirdly, the ingredients must be digestible. Slabs of overcooked, unleavened bread too hard to bite or chew do not make a good sandwich. Soft bread is best, but crackers or ‘Ryvita’ are ok for some tastes.
Given that the transformation of dead organic matter into compost depends on decomposer organisms, it stands to reason that you will get the best results if you provide the conditions they prefer. Although there is a huge diversity of decomposers and they seem so alien in many ways, the ones we want to encourage are biochemically very similar to people, and need oxygen, water and the right sorts of food. Without these they will fail to thrive and will eventually die.
What happens when the materials are combined ‘correctly’ is that the structural rigidity of the ‘bread’ maintains a complex pattern of air spaces which allows the decomposer organisms to breathe, and as it breaks down, supplies them with energy. The ‘cheese’ provides nitrogen-rich food, and moisture which fills the spaces with humidity without waterlogging. So we have air, water and a balanced diet, and the decomposers are able to multiply quickly. In a large heap constructed all at once, the heat generated by all the metabolic activity cannot escape fast enough and the temperature rises. This favours fungi and bacteria (thick-bordered boxes) and excludes larger organisms. If the heap is small or assembled over a longer period the heat escapes and the temperature, as in most natural situations, is not much higher than the surroundings. This situation favours a full range of decomposers, enabling the material to be broken up quickly. Bringing in material from outside to heat the heap really doesn’t make sense. Cool composting is the prudent third way — a low effort composting system that works.