Yes, the vacuum seal helps, but there is always air trapped to a degree.
As the bag heats, the air expands. Usually not major, but can cause FLOATING.
If the bag floats, the TOP part may not be heated above 128!!!
I simply place a plate on top of my meat, and that keeps it weighed down.
And my wife lost the blade protector on my unit, so I had to use the backup unit.
I went online… And bought a new Sous Vide (always have to have a backup), WITH DELAYED START! Woot Woot!
So, now I can pre-cook. Freeze. Later drop it in an ice bath in the sous vide, with a delayed start, and then add 30-60 minutes to the re-heat time… And SAFELY have my food when I need it done…
So excited. 3 racks of ribs packaged, 2 in the sous video right now, 1 rack frozen.