Why is cake fluffy?

Have you been helping with baking lately? The kitchen is like a home science laboratory where experimentation can happen.

  1. Gather two ziplock bags, bicarbonate of soda, vinegar, dry instant yeast, sugar, some lukewarm water and take them to a space where its ok to get a little bit messy.
  2. Add a few teaspoons of bicarbonate of soda to one ziplock bag, half-close the ziplock then pour in some vinegar and quickly close the bag completely.
  3. Take a second ziplock bag, add a teaspoon each of sugar and yeast then carefully pour in water to about halfway. Zip the bag closed.
  4. Did both bags act the same way? How long did it take for the second bag to fill with gas? Do you think the water temperature or the amount of yeast might change this?

Often when we bake, we want things to be light and fluffy – think about some bread you’ve had. It has lots of little holes in it. Those holes come from bubbles; pockets of gas that were trapped in the dough while it baked. Sometimes those little bubbles come from yeast. Yeast is actually a living thing. You feed it sugars, and it essentially farts out gases. Those gases make the little bubbles in your mixture. Delicious!

Our Scienceworks challenge to you

What else can you mix together in the kitchen to cause a fizzy reaction? You’ll need an adult to help with this one!

Find a small container with a tightly-fitting lid that pops off instead of screw-top - a film cannister is perfect if your parents still have one! Ask your adults for some effervescent or fizzy tablets like alka seltzer. Add half a tablet to the container, some water and close the lid completely and flip upside down.

Quickly stand back and watch and wait - this one is loud and messy!

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