[alkonaut]

I fully expect plastics labelled with e.g "up to 90 degrees C" to not release anything unwanted into my food if I stay well below that temp. I'd also expect the label to have a wide margin to dangerous temperatures.

In theory you can use anything that handles the temperature, such as silicone. You could in theory force your food into a jar with a bit of oil.

[pflanze]

You might be making matters worse with a jar: those with screw-on lids have a plastic lining in the lid that's traditionally PVC with plasticizers which are considered to be bad for health. To make matters worse, oil will support the migration of the plasticizers out of the plastic.

[dpeck]

food in jar with oil = confit, a fairly popular, and very long lasting, preparation in the sous-vide at home world.