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Hands-on Activities

Why are peas and corn classed as starches on food guides?

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What You Need

  • 1% iodine solution (can be found at the pharmacy)
  • Samples of starchy foods – flour, bread, cooked or fresh pasta, lightly coloured cookies
  • Samples of fruits - apples, bananas, tomatoes, lemons
  • Samples of vegetables including – potatoes, peas, corn, cauliflower, onions

Safety First!

Wear safety goggles when working with iodine. Make sure to wash your hands with soap and water once the testing is complete.

Make sure to avoid the foods to which you are allergic or intolerant.

What to Do

  1. Take a small amount of a food that belongs in the starchy food group and put one or two drops of the iodine solution onto it. What happens?
  2. Repeat this with other foods belonging to the starchy food group.
  3. Test small amounts of different foods in the other groups with the iodine and record what happens. For best results, remove the skins, peels or husks of fruits and vegetable before adding the iodine.
  4. Based on your results, to which food group do peas and corn belong?


What’s happening?

When iodine comes into contact with a starch it produces a deep blue (or blackish) colour. We can use the iodine to test whether foods are starches or not.

You can see that all foods in the bread group give a blue colour with iodine-- all starches belong in the bread group. This experiment shows us that some vegetables have a considerable amount of starch in them. Some of them have so much starch that they are usually categorized with the bread group on food guides.

Why does it matter?

Starch is made of very long strings of sugar molecules. It is produced by plants as a way to store energy. It is common in many of the foods we eat.

If you are trying to balance your food intake, you must remember that certain vegetables are considered starchy foods and they do not count as vegetable servings according to Canada’s Food Guide.

Investigate further
  • Try the iodine test with samples of other foods that you eat regularly to see if they have a high starch content.