Sunday, February 5, 2012

Bananas and balloons

J goes on banana kicks.  He loves them, and then he won't eat them for weeks.  He's doing the latter at the moment.

So, we decided to make an experiment from one of our rotting bananas.

I took the idea from the book, The Everything Kids' Science Experiments Book, which happens to be my favorite Christmas present I received this year.  Don't worry, I have a review in the works to give some opinions on this book and twists to toddlers and preschoolers (it's geared for 8+).  I hope to finish this review in the near future.

Anyways, it's a fairly easy set-up.  You mash up a very ripe (think brown) banana, stick it in a bottle (we used one of our many 20oz soda bottles), pop a balloon over the top of the bottle, and document the process.  The book recommends putting it outside in a sunny place to expedite the process.  However, we live in an apartment complex with a lot of boys who have potential of screwing up well planned science experiments...and it's not really "warm" outside, mid-60s at best.  Our apartment has been ~70 deg during the day, but the balloon hasn't been exposed to sun.

Peeling the bananas

Mashing it up with a spoon

We documented through pictures and also by measuring tape once the balloon inflated enough to measure:

Monday 1/30: Set-up the experiment

Tuesday 1/31: no noticeable change in balloon

But, there's some icky changes going on with the banana (there was some bubbly action)

Wednesday 2/1: balloon is a little more full, but still sad looking

Thursday 2/2: Balloon stands up!  J is excited that science is working.

And take a look at that gross banana mush.

Friday, 2/3: Began balloon measuring - 5 cm

More bubbly grossness in the banana mush:

Saturday 2/4: 5.2 cm

Sunday 2/5: 5.2 cm (no change, no new pic)

I'll leave the bottle alone for a week and report back next weekend.

What's going on?  As the banana decomposes/decays, it's releasing gas which wants to escape the bottle but is trapped by the balloon.  It puts pressure on the balloon, causing it to inflate.

Our Personal Extensions:
Trying this experiment during the summer inside and out (assuming we find a safe "sunny" location).  We'll compare them to each other and to the growth of the balloon during the winter inside.  Maybe we'll try one at the same time in the fridge too.  Stay tuned for another banana and balloons post over the summer.

We'll also try a smaller bottle and/or more bananas for hopefully a more dramatic response.


  1. This sounds so cool! The banana mush gets really gross though! Were fruit flies a problem?

    1. The balloon closes off the bottle opening very well. We didn't have fruit fly problems, but we did mush up the bananas before they got to the fruit fly stage on the counter :-). Let me know how your experiment goes.

  2. Left a shake I made in the car. Fell under the seat for 10 days.

    When I opened the container to clean it, it popped like a champagne bottle. Scared us lol.

  3. I tried this experiment recently with my son recently after finding it in the book "Dad's Book of awesome Science Experiments". But after more than a week we have no results. The only thing I think we did differently is we included the chopped up peel in the mush. I am wondering if there is some bacteria-inhibiting property in the peel.