Growing Microorganisms – Dirty Potatoes

Welcome to more Spectacular Summer Science, today we’re growing microorganisms

Following on from our hand washing exercise last week we tried another related activity. We boiled some potatoes to destroy any microorganisms already present on the surface and then touched one of them with dirty hands leaving the other untouched.

What would you expect to happen?

Our hypothesis was that micro-organisms from our hands would have been transferred to the potato when we touched it, and so that one should grow more bacteria than the clean potato.

We also added a potato left in the air and one in vinegar to see what would happen.

What you need:

  • 2 small potatoes sliced in half
  • Boiling water – get an adult to help
  • Vinegar
  • 4 containers


  • Boil the potatoes for a few minutes, this is to destroy any microorganisms already present on the skin.
  • Carefully remove one potato with a spoon and place into a jar, cover the jar and label it. This is the clean potato.
  • Remove another potato but don’t cover this one, we are exposing this potato to the air.
  • Remove a third and place in a jar containing vinegar.
  • Finally remove the last potato, let it cool enough to hold and then rub it around your hands, before placing in a sealed jar.


Leave the jars on a window sill for a few days and observe and changes.


The potato exposed  shrivelled up a little bit, and there is some evidence of micro-organism growth.


The clean potato, ended up quiet slimy, with some possible micro-organism growth.


The dirty potato didn’t seem to have more more evidence of micro-oroganism growth than the clean potato.


The potato kept in vinegar looked mostly unchanged.



You can see that the vinegar has definitely preserved the potato. This is because vinegar is an acid and microorgansims find it hard to grow in such a hostile environment. That is why we pickle things to make them last longer.

I was hoping to see more growth on the dirty potato, but with science things don’t always work out as you expect. It could be that my jar wasn’t airtight, or it hadn’t been boiled for long enough so there were still some bacteria on the surface.

The healthy schools project has more information about good hygiene.

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Spectacular Summer Science

Week 1

Day 1 –  Baking Soda Ice Cubes

Day 2 – Slipping and Sliding

Day 3 – Fun Heart Rate Investigation

Day 4 – Mini Beast Hunt

Day 5  – Pretty Flowers

Week 2

Day 1 – Splatter patterns

Day 2 – Monster Tea Party

There are 3 comments

  1. Pinkoddy

    What a great experiment. Think the boys would love this but can’t see my husband liking growing germs on his window sill. May try this as an outdoor experiment. Thank you for sharing.

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