“… [M]odified atmosphere packaging (MAP) … involves either actively or passively controlling or modifying the atmosphere surrounding the product within a package made of various types and/or combinations of films … Edible films may consist of four basic materials:lipids, resins, polysaccharides and proteins …  The most common plasticizer used to cast edible films is food-grade polyethylene glycol, which is used to reduce film brittleness … Gelatin is … extracted from the boiled crushed bones, connective tissues, organs and some intestines of animals such as domesticated cattle, chicken, and pigs.”

Another theory floating about is that this coating isn’t really a coating at all, but rather an entirely natural occurrence, referred to as “epidermal peel,” caused by cold weather. Lettuces in particular appear to be affected in this way when exposed to frost conditions. Epidermal peel can be likened to “chapped lips,” in that the outer layer of a leaf will get damaged by freezing temperatures, causing a layer to peel away from the leaf. This peeling is typically considered unsightly, and harvesters will typically remove as many of the affected leaves as possible.