Leftovers took on moral urgency in World War I, when the United States launched its first formal international food-aid program. Intended to provision European allies in regions where the war had upended food production and distribution, the initiative included a home-front conservation campaign focused on getting Americans to eat their leftovers. Propaganda instructed housewives to use up every crumb and to cook leftover-incorporating dishes such as goulashes and casseroles.

In their zeal to send whatever food they could to war-torn Europe, a lot of individuals went further still. Some said restaurants should resell the uneaten food scraped from dirty plates. Others argued that it was immoral to keep pets because they ate food that could be used to feed hungry Belgian babies. (A neutral country invaded by Germany at the beginning of the war, Belgium was, to Americans, the prototypical victimized country.) That was true, at least in theory; at the time, American dogs and cats lived mainly on human food past its prime, such as stale bread and souring milk. In wartime, some Americans actually killed their pets rather than continue feeding them leftovers, and newspapers across the country celebrated them as patriots.

Leftovers’ patriotic glamour dimmed in peacetime, however, and by the mid-1920s Americans were openly discussing the “problem of leftovers,” a new source of annoyance as food prices fell and home refrigeration became almost ubiquitous. As abundance democratized leftovers, wealthy people increasingly went out of their way to emphasize that they rarely ate them. For instance, some white southerners publicized the fact that they sent their domestic servants home with the leftovers from their own dinners. Never mind that those same employers used that practice—“pan-toting,” as it was called—to justify wages whose miserliness could not possibly be made up for by somebody else’s leftover food.

But another wave of pragmatism set in during the Depression, when, at the same time that tens of thousands of Americans were investing in The Joy of Cooking’s economical cooking advice, radio broadcasts sponsored by the U.S. Department of Agriculture reminded listeners of the crucial importance of eating leftovers in lean times. “Of course, if you’re the wife of a multimillionaire, you probably won’t bother much about leftovers,” winked one broadcast. For everybody else, making the most of leftovers was both important and potentially pleasurable. And that pleasure came from creativity.

In fact, the economic imperatives of the Great Depression helped to usher in a golden age of leftovers, a three-decades-long stretch that was inspired by the family budget but sustained by aesthetics. Then, if it was a good thing to reheat leftovers, it was even better to mix them with sauce and sculpt rice rings around them. Transformation was key. Leftovers of all kinds could be hidden in a potpie, blanketed in crepes, chopped up and molded into meat loaf.