Get a rise out of your dough with a simple acid-base reaction!
Safety: When dealing with food, use clean hands and clean equipment. Be safe when using the oven, wear oven mitts and ask an adult to help you out. Be careful when using a sharp knife to cut up your scones and ask an adult for assistance with this step.
You will need
- 3 cups all-purpose flour
- 1 teaspoon salt
- 1 teaspoon baking soda
- 1 teaspoon sugar
- 1½ cups buttermilk (alternatively, milk with 2 teaspoons lemon juice)
- Jam and cream to taste
- Baking tray
- Baking paper
- Large mixing bowl
- Large chopping board or clean surface
- Oven mitts
What to do
- Pre-heat the oven to 210 °C and line a baking tray with baking paper.
- In the mixing bowl, whisk together the flour, salt, baking soda and sugar.
- Slowly add the buttermilk, bit by bit, until the dough mixture is wet but not too sticky. You might not use all of the buttermilk.
- Sprinkle generous amounts of flour on the chopping board and then put the dough on top. Knead it for a minute or so (see steps below). If the dough gets sticky, sprinkle flour on top of it and keep kneading.
- Gently pat the dough into a disc about 2-3 cm thick. Then, use a knife to cut the disc into triangular eighths – ask an adult for help with this step. Space these triangles on the baking tray a few centimetres apart.
- Bake the scones for about 18-20 minutes or until they are golden on top. How tall did the scones get?
- Let them cool for about 10 minutes, then try a bite of your creation. What flavours do you notice? Now add the jam and cream, but don’t go overboard!
Heat and expanding carbon dioxide gas turned your dough into a fluffy delicious treat. We often think of carbon dioxide as waste breathed out by many living things, including us. So where did the carbon dioxide in the scone come from?
In scones, the key to rising dough lies in combining an acid with a base. An acid is a substance that gives off hydrogen ions (H+), which we taste as sour. A base is a substance that takes up H+ ions, which we often taste as bitter. When we combine an acid with a base, it triggers an acid-base reaction where both substances change as they exchange H+ ions.
In this activity, you combined acidic buttermilk with basic baking soda, which kicks off an acid-base reaction that produces a lot of carbon dioxide gas. In chemical terms, the buttermilk supplied H+ ions which were taken up by the baking soda (also called sodium bicarbonate). This chemical reaction caused the baking soda to break down, releasing its carbon atoms as carbon dioxide gas and giving your scones a rise.
Try a bite or two of your baking soda scone with jam or cream. Then close your eyes, and focus on what you taste! Be your own food critic and write down your observations.
Did you detect a slight tang? Tangy or sour flavours can come from the acid in buttermilk called lactic acid (or citric acid if you used lemon juice). Lactic acid is a by-product of the probiotic microorganisms added to milk to make buttermilk. It’s the same acid created by your muscles under intense exercise!
Did you detect any bitterness? Baking soda is bitter so ideally, a baking soda scone recipe should call for enough acid to react with all of the basic baking soda. It’s important to whisk your dry ingredients thoroughly to avoid clumps of baking soda that can’t react with the buttermilk.
Did you detect sweetness? Unlike yeast breads, microorganisms aren’t eating significant amounts of sugar. This recipe calls for the same amount of sugar as the Yeast bubbled bread activity but probably tastes a lot sweeter. Note that buttermilk also contains sugars.
What else do you taste? Food is chemistry you can eat!