Last winter, teams of researchers in three U.S. cities donned goggles, gloves, and respirators, tore into bags of other people’s household garbage, and then pawed though the contents. Separating slimy banana peels from clumps of coffee grounds was dirty work, but it had a laudable goal: trying to get a handle on how much food waste could have been consumed or diverted before winding its way into the waste stream with a one-way ticket to the dump.

The problems associated with urban food waste are …