lesson
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If you look at a slice of potato and a chunk of cheese, they look totally different — but both hide invisible chemical fuels called nutrients, which are substances your body uses for energy and growth.
How can food scientists tell which food contains starch for slow-release energy and which contains fats without tasting them?
The Iodine Test for Starch
Starch is a type of carbohydrate that plants make to store energy, found in large amounts in foods like potatoes, rice, and bread.
To find starch, scientists use an indicator — a test liquid that changes color when a specific nutrient is present.
In 1814, French chemists Jean-Jacques Colin and Henri-François Gaultier de Claubry discovered that yellow-brown iodine solution turns an intense blue-black color the instant it touches starch molecules.
📊Interactive/visual science lab diagram illustrating the Iodine Starch Test. Top banner shows 'Iodine Test: Starch Detection'. Left side: Dropper bottle with amber/yellow-brown iodine solution. A drop falls onto a potato slice, turning dark blue-black on contact with label 'Positive Result: Blue-Black (Starch Present)'. Right side: A drop falls onto a cucumber slice, staying yellow-brown/amber with label 'Negative Result: Yellow-Brown (No Starch)'. Safety icon in the corner: Goggles and 'Do Not Taste' badge. Clean, modern flat-card UI with high contrast, light gray card background #ffffff, border #e2e8f0, text #1e293b.
For safety in the lab, always wear protective goggles and never eat any food tested with iodine, because iodine can be poisonous if swallowed.
What happens if a food doesn't have starch, but is loaded with cooking oils or butter instead?
The Paper Spot Test for Fats
Fats (also called lipids) are rich energy-storage nutrients found in butter, oils, nuts, and meats.
To test for fats, you rub a small sample of food onto plain brown wrapping paper or blotting paper, let it sit for ten minutes, and hold it up to a light bulb.
While a drop of water dries up and leaves the paper opaque (blocking light), fat permanently soaks between paper fibers, making the spot translucent — meaning it lets light glow through.