How to prove that there is air in a piece of dry bread?

If you take water into any vessel and put a piece of dry bread on it, then it will be afloat for some time. This suggests that it contains a lighter element than water, namely air.
Then, after a while, the dry piece will begin to gradually soak and go to the bottom.
At this moment, with its smooth immersion, bubbles will be released.
As a result of the fact that air molecules are lighter than water molecules, they will rise upward, escaping from the water mass.