Film Lid On Packaged Food Swelling Up

[koster]

If you've got some pre-packaged food in a plastic container with a film lid, stored in the fridge, and the film lid has risen up as though there's more air inside - is this a sign it isn't safe to eat? What is it that causes the lid to rise?

[excelsior-1]

it is caused by the emission of gases from the decay --- the food is no longer fit to eat

[EDDIE51]

It is the food starting to decompose and give off methane , I would bin it.
Is it 'in date' still?

[boxtops]

If that starts to happen in our fridge, I bin it straight away. Some foods do that earlier than others.

[koster]

In this case it was a chicken meal, one day past the Use By date. I was surprised that it went like this so soon, because I thought that supermarkets would be slightly over cautious (one day anyway) with the dates.