How is the meaning fermentation related to the word bubble?

During fermentation, yeast usually consumes sugar and converts into ethanol (ethyl/drinking alcohol) and carbon dioxide gas. This phenomenon is usually observable during the process of making bread (letting the dough rise) or brewing beer (adding yeast into a liquid that contains sugars that come from boiling malted grains [malting is a process in which the seeds be allowed to partially germinate to convert the contents of the grains into sugar] to release the sugars into the water).