The day food scraps become infrastructure — a map for seven days on composting

Most writing about composting begins with first principles. Aerobic microbes break organic matter down, the pile heats, humus remains; you balance carbon against nitrogen and keep the moisture in range. That account is accurate and self-contained, which is why what it leaves behind is an impulse to try it rather than a question about how to design a system. In the 2020s, though, the centre of gravity of the argument moved. Composting as it now appears in government documents is not a story about microbes but about collection frequency, capture rates, contamination rates, gate fees and emission factors. The same bucket has moved, within a decade, from being a hobbyist's tool to being an object of law.

The series assumes an earlier column, Composting: the science and the societies, which covered the science of decomposition and the collection-and-composting systems built in Japan, South Korea, Taiwan, Europe, the United States and India. None of that is repeated here. What this series takes up is the part that understanding the principles does not solve. Why, in countries that made separation compulsory, do the scraps still fail to arrive as expected? Who pays to build a processing plant and what revenue keeps it running? What actually decides whether a given tonne of food waste becomes compost or becomes methane for a generator? And how much substance is there in the charge that finished compost is itself a source of contamination? Seven days, in that order.

Why the 2020s? Looking for a single cause will mislead. At least three independent currents happened to converge on food waste at roughly the same moment. The first is climate targets: policy attention shifted from carbon dioxide alone toward methane — short-lived but powerful — and landfills were named as a major source of it. The second is the codification of food loss: countries translated an international goal into domestic statute, and a moral intuition about not being wasteful turned into numerical targets and reporting duties. The third is the physical container itself. Landfills are extraordinarily difficult to open, existing capacity is finite, and organic matter consumes volume while generating leachate and odour.

The three move independently. From the climate side, the objective is to keep organic matter out of landfill; whether it becomes compost or is digested for energy is a choice of means. From the legislative side, what matters is reducing the total generated, while the treatment of what is nonetheless generated falls under a different statute. From the landfill's side, the value is simply volume avoided. That the three objective functions do not coincide is a fact that will resurface repeatedly across this week. Where mandates stumble, and why compost and methane compete for the same tonne, both trace back to it. Today we set the three layers out separately and ask what each of them is actually demanding of a bag of food scraps.