HomeArticlesSari on Science: Super-secret spy messages ... via banana!

Sari on Science: Super-secret spy messages … via banana!

My daughter started kindergarten this year, so I’m packing her daily lunches for the first time. As I was admiring our new collection of bento boxes and character lunch bags, I started brainstorming other ways to make her lunches extra special.

I love the idea of including a personal Post-it note, but I needed an idea for a little one who can’t yet read. I recalled this fun activity, which creates a secret science opportunity for any age. So grab a banana! We’re about to have a bunch of fun using science to create super-secret spy messages.


  • Banana(s) — yellow with no brown spots work best
  • Bamboo skewer or toothpick
  • Timer (optional)
  • Imagination (required!)


  1. Gently lay a banana on its side to use the broadest surface to write on.
  2. Use a skewer to carefully scratch a message and/or pictures onto the banana skin. Don’t break the skin; pressing on it gently will do the trick.
  3. Watch your banana as the message or image begins to emerge in dark brown or black. Optional: Use a timer to track how long it takes for the message to develop.
  4. Slip the banana into your favorite person’s lunch box for a surprise.

What’s happening?
When the cells of the banana skin are damaged (cut, bruised, scuffed, etc.), the cells release a chemical called polyphenol oxidase, which reacts with oxygen to produce brown pigments.

Bananas also produce ethylene gas, which speeds the ripening process by breaking down cell walls, continuing the browning process as the banana ripens. Try comparing how long it takes a banana with a message to go completely brown versus an unmarked banana. Is there a difference?

Did you know?
Bananas are among the most popular fruits in the world, running neck-and-neck with tomatoes.




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