i m sure they might explode. Some people regularly open these jars to let the pressure off, close them, then shake them (to cover the top air space with the liquid to wash over bacteria from air or mold-spores) and close the jars again.
my brother once had an explosion. He tried to make fruit wine (different kinds slushed and mixed into pulp). He use a wide (belly-round) bottle with a self made airlock-seal (it looked like the ones above). As far as i remember, the airlock worked, you could see little bubbles in the water of it.
but theeeeeen .... when he tried to open the cork, it exploded into an geysir which hit the room-ceiling... nice, yucky, sticky, smelly
i am thinking about making airlocks: just drill a hole into cork or bottle-cap. put a lenght of plastic tube into it. seal the tube to the cork/cap. put the tube into a bucket or bottle with water. Would that work?
blesses
tobias