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There seems to be two different ways of storing food in bowls with plastic wrap between countries (Saran wrap, Cling film etc). Method 1 is to stretch the film tightly over the opening of the container, leaving an air gap between the food and the film inside the container. Method 2 is to place the film directly over the food and press it onto the side of the bowl, thereby creating a seal and eliminating any air gap.

All things being equal and the risk of modern films leaching plasticiser being minimal, what are the pros and cons of each method? The only benefit I can see from Method 2 is that it would prevent any skin forming on custards etc. That is the only downside I can see for Method 1, although it does entirely remove any risk of plasticiser contamination. Method 1 also provides a slightly better seal, especially if the container has a lip.

(Confession: I'm a diehard "Method 1" man. Part of my childhood amusement was to "Ping" the taught film on various dishes, as pitched by the advertisers of this new technology at the time ('It stretches as tight as a drum')).

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    I suspect the ingredients might be a factor. Technique 2 is going to be better for foods that might oxidize as you don’t trap as much air in there
    – Joe
    Sep 19, 2022 at 0:50
  • Also of note: I have lids for most of my bowls, so don’t need to do the first one, only the second occasionally. My larger use is wrapping stuff tightly before freezing
    – Joe
    Sep 19, 2022 at 0:52

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Method 1 will usually allow for a water-tight seal along the container-film interface, good for when you expect sloshing of liquid contents. It'll also slow down cooling of contents in a refrigerator as the headspace forms an insulating layer - instead of a food<>cold air heat transfer interface, you'll have:
food<>warm air<>film<>cold air
for multiple heat transfer interfaces, with the film surface area a likely limiting variable - before even considering vapour enthalpy.

Method 2 allows for the film to conform to the food surface, and when done correctly eliminates insulating headspace. As you noted, it will prevent skin formation from dehydration, and as @Joe noted it will inhibit oxidation - it's the ideal method for guacamole.

Another effect for method 2, as a non-polar surface, is that the film can adsorb certain non-polar compounds. For example, it can pick up unwanted green or yellow lipid-soluble pigments on the surface of a cream soup, or the 2,4,6-trichloroanisole responsible for cork taint in a glass of wine. A downside effect is that it can wick oils from the surface of the food over the rim and onto the exterior of the container.

My preference is method 1 with two opposing sides lifted for convection then sealed when fully cooled, and method 2 for for specific use cases.

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