Few home experiments get a bigger reaction than a tower of colored foam erupting from a bottle. The elephant toothpaste experiment is sold in plenty of kits, but you don’t need one. Grocery-store hydrogen peroxide, a packet of yeast, and dish soap will do it. This guide follows the methods published by the USDA Agricultural Research Service and the American Chemical Society, and explains the chemistry behind the foam.

Like every project in the 25Pages experiment collection, it follows the same loop: predict, test, record, explain.

Make a prediction first

Hydrogen peroxide breaks down on its own, just very slowly. What do you think will happen when you add yeast? How high will the foam rise? Would more yeast make it faster, or bigger? Write your guesses down.

What you need

These quantities are from the USDA recipe:

• ½ cup of 3% hydrogen peroxide (the standard drugstore strength)
• 1 tablespoon of dry yeast
• 3 tablespoons of warm water
• 1 tablespoon of liquid dish soap
• About 10 drops of food coloring
• An empty plastic bottle or clear vessel
• A cookie sheet, tray, or dishpan to catch the foam
• Measuring spoons, a small cup, and safety glasses

Step-by-step

1. Put on safety glasses and set the bottle on the tray. Outdoors, a kitchen, or a bathroom all work. It’s messy.
2. Add the dish soap to the bottle, then pour in the hydrogen peroxide. Swirl gently to mix.
3. Add the food coloring. For a striped effect, drip it down the inside walls of the bottle.
4. In a separate cup, stir the yeast into the warm water until it’s a smooth slurry. The ACS version lets the yeast sit in warm water for at least 5 minutes, and stresses that the water must be warm.
5. Pour the yeast mixture into the bottle quickly and step back. The ACS puts it simply: don’t get too close to the bottle.
6. Watch the foam climb out of the bottle and spill across the tray.

The science: a catalyst at work

Hydrogen peroxide (H₂O₂) naturally breaks down into water and oxygen gas. The USDA explains that this normally happens slowly, which is why peroxide is sold in dark, opaque bottles that block light. Yeast contains an enzyme that speeds the reaction up dramatically. USDA identifies it as catalase, which is found in most living things that use oxygen. It’s the same enzyme that makes peroxide fizz on a cut or scrape.

An enzyme like this is a catalyst: a substance that makes a reaction happen faster. The American Chemical Society’s Middle School Chemistry lesson points out that the catalyst’s atoms don’t become part of the products. The reaction is:

2 H₂O₂ → 2 H₂O + O₂

So where does the foam come from? The ACS explains that the dish soap traps the oxygen gas as it’s released, turning it into millions of bubbles. Without soap, the oxygen would simply escape into the air. The foam lets you see that a gas is being made.

Turn it into an experiment

The ACS suggests predicting how the reaction will change under different conditions. Change one thing at a time, and measure the foam height against a ruler or tape on the wall:

• Yeast amount: try ⅛ teaspoon, the ACS amount, versus 1 tablespoon, the USDA amount.
• Water temperature: compare warm water with cold water for activating the yeast.
• Bottle shape: USDA suggests trying different-sized vessels. A narrow neck makes a taller column.
• No soap: run one trial without dish soap and watch what happens to the oxygen.

Safety notes

• Use only 3% household hydrogen peroxide. Higher concentrations, like those in some online demonstrations, are hazardous and not for home use.
• Wear safety glasses, and keep your face away from the bottle when you add the yeast.
• USDA notes that peroxide can bleach fabric and food coloring can stain, so wear old clothes or an apron.
• If any mixture gets on skin or clothing, rinse with cool water. Don’t eat or drink the foam.
• USDA says the finished foam can be washed down the drain with water or thrown in the trash. Wash all tools with warm soapy water.
• Children should do this experiment with an adult.

Check your prediction

Did more yeast make the foam rise faster? Did the soap-free trial produce foam? Explain your results using the words “catalyst,” “oxygen,” and “enzyme.” Then you’ll understand the chemistry, not just the eruption.

Skip the single-use kit

Experiment kits are fun once. A guided library keeps you experimenting for months. The DIY Blue Book of Experiments 2026 Standard Edition ($347) is the core hardback collection of hands-on projects. The DIY Blue Book of Experiments MMXXVI Editor’s Edition ($480) connects each experiment to the science of everyday life. See every title at 25Pages.com.