Cooking & Science

Study rising bread:

Yeast is a kind of fungus that breaks sugar down into smaller components. Mixed in with bread dough, the yeast converts sugar molecules into molecules of carbon dioxide (CO₂), alcohol (this evaporates in the oven), and water. The CO₂ expands and creates small gaseous bubbles that cause the bread to rise. The more CO₂ in the bread, the faster it will rise. In your laboratory-kitchen, you can experiment to discover what conditions cause the yeast to produce CO₂ the fastest, and thus make the bread rise faster.

First you should form a hypothesis: predict under what conditions the yeast will most quickly make CO₂. Do you think it will work best in hot and dry conditions? Cold and damp? Write down your idea.

A scientist will not only record his procedure steps and results, he will often draw pictures as well. Use a magnifying glass to look at yeast, and draw a picture in your notebook. After your bread dough is mixed and kneaded, cut off a cross section of the dough and draw a picture.

Divide your dough into three oiled bowls and cover them with towels. Place one bowl on the counter, and another on the door of the oven with the oven set to its lowest setting (about 150 degrees). Place your third batch in the conditions that you predicted at the beginning. (If you said cold and damp, put it in the refrigerator.)

When each batch has doubled in size, write down the time it took to rise. (This will happen at different times.) Cut another cross section and see if the dough looks different from when you looked at it before, then pound it down again and put it in a bread pan. Let the dough double its size again, recording the time.

When you are done and enjoying your fresh bread, think about your hypothesis. Were you right? Which batch of dough rose fastest? What conditions caused the yeast in that batch to create the CO₂ the fastest? What can you do next time to increase your knowledge of rising bread? You could try using a thermometer to check the temperature every 15 minutes to see if it changes while the bread is rising. To more clearly show the effect of temperature on rising bread, try changing the position of your batches of dough: move the batch on the stove door to the refrigerator and move the batch in the fridge to the stove door. Observe how the change in temperature effects the rate of rising. Record all your results, and form conclusions from your data.

Study crystallizing candy:

Pioneer families used to make delicious candy by pouring maple syrup on snow. When the snow cooled the maple syrup quickly, it caused crystals to form. The crystals in candy are bigger or smaller depending on how fast the syrup cools. In this experiment you can make candy while trying a couple of different methods to cool the syrup. See whether you like big crystals or small crystals better!

First, predict whether faster cooling or slower cooling will make larger crystals. Do you think large crystals will make the candy harder or softer? Remember to record your predictions and observations.

Place a pan of water in the freezer to make a sheet of ice, and set a sheet of wax paper on the counter. Boil the maple syrup until it becomes thicker and more concentrated. (Be careful not to burn it.) Pour some of the concentrated syrup onto the sheet of ice and some onto the wax paper. If you have snow, you can also pour syrup on some clean snow.   When your first batch of candy is the same temperature as the ice, take it off and look at it under a magnifying glass. Draw any crystals you see. Do the same thing for the syrup on the wax paper and the snow. Does the candy look the same? Does it taste the same? Check to see if your predictions at the beginning were correct.

• Find out more with these Kitchen Science Projects!