Today’s [salad] bags are a triumph of practical ingenuity. Their plastic is made of up to five to ten layers, each with a different function. Some are designed to make the package shiny or crinkly, others to carry print well. Together, they have to be just permeable enough to keep the bag’s artificial atmosphere in balance – the wrong ink alone can suffocate a salad. As the lettuce sits on the shelf, the gases in the bag are constantly consumed, released, and replaced. Oxygen, nitrogen, and carbon-dioxide molecules bond with the polymers on one side of the plastic and are released on the other, diffusing from high concentrations to low. Every type of salad requires a different type of bag, tailored to its respiration rate by gas chromatography and computer analysis. Every bag is a miniature biosphere.
That’s from the recent double-issue of The New Yorker, Sept. 6, p.140; it is devoted to food and may be the finest issue yet under Remnick’s tenure. And here is a brief defense of eating from salad bags.