The Rookery

A week ago Wednesday when we were trapped inside by a Thunderstorm, we set up some experiements with yeast.  The first balloon to expand with CO2 was from our 20g mashed banana and yeast bottle (at 116 degrees).  Soon, the other sugar and yeast bottles caught up to it, even the 140 degree bottle where some yeast had survived our attempt to cook them.  In the next few days, the balloons mostly deflated — which we attributed to poor seals or the fact that gasses can (slowly) permeate vinyl balloons – especially those bought at the dollar store.

 

But then the banana balloon began to get pulled back down into the bottle.  We'd pull it up and it would get sucked back in.   "A vacuum" one child announced.  But why?  Were there more microbes on the banana that are somehow consuming the CO2…or another gas in the bottle?  Is the water carbonated?  Why didn't the other balloons do it?  WHAT'S GOING ON?!?

 

These are not rhetorical questions — we're really curious.  We've left the experiment up over the weekend to see what happens.  (I'll admit that it was only through my laziness that we hadn't cleaned it up already…isn't that how penicillin was discovered?)

 

Anyone have any ideas?

 

Update on the update:

Turns out that the search query "banana and yeast experiment vacuum" actually yields a surprising number of results.  We live in a remarkable age.  This might lead us to our next steps:  Science Buddies