Does the word ‘science’ make you think of white coats and laboratories, microscopes and bottles of chemicals? Sometimes we forget the science we work with on a daily basis. How did a cucumber become a pickle? Why does bread rise? Why does fruit turn brown when you cut it and leave it out? All of these questions are pondered in the kitchen—and they all have scientific answers. You have your own scientific laboratory in your home, so head on into the kitchen! The following are a couple of kitchen experiments you can perform. These ideas and many more are contained in the book Cooking & Science by Joseph Julicher.
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:
If you’ve ever read ‘Little House in the Big Woods’ by Laura Ingalls Wilder, perhaps you remember when Laura and her family poured maple syrup onto the snow to make candy. 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 try 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, just like Laura Ingalls did! 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.
Science Lesson: Polymers & Slime
Polymers are very large molecules, formed by repeated patterns of chemical units strung together. Although ‘polymer’ might bring to mind rubber or slime, did you know that there are polymers all around us, including inside our bodies? The protein DNA, which is the ‘blueprint’ for cellular reproduction, is a naturally-occuring polymer. The protein casein, in cow’s milk, is a polymer as well. Other natural polymers are cellulose and starch. Bone, horn, cotton, silk, rubber, paper, and leather all come from naturally-occuring polymers!
There are manmade polymers, as well. Fabrics such as rayon and polyester, polystyrene (used in styrofoam coffee cups), and PVC (used in pipes) are common examples of these artificially-occuring polymers.
You can use the following recipes to learn more about non-edible, naturally-occurring polymers.
Did you know you can make glue using the polymers in milk protein? In a glass, put seven tablespoons of non-fat or skim milk—whole milk contains more fat, which can change the experiment results. Add a tablespoon of white vinegar to the milk; you should see solids begin to form suspended in the liquid. The solids will have a grainy appearance. Allow them to settle toward the bottom of the glass, then drain the liquid off, using a coffee filter or paper towel. Now, pat the solids with a paper towel to absorb any excess liquid. You can use the resulting slimy substance as glue—coat two pieces of paper with it, stick them together, and let it dry. How well does your homemade glue work compared to other glues?
When you added the vinegar to the milk, it caused the milk’s protein, the polymer casein, to separate from the liquid part of the milk and clump together to form solids. Casein is used in adhesives, paints, and even plastics.
You can make a slimy substance using milk, vinegar, and baking soda. Form solids like you did in the glue project, using seven tablespoons of milk and one tablespoon of white vinegar. After the solids have formed within the liquid, use a coffee filter or paper towel to drain off the remaining milk. Gently squeeze the filter or paper towel to wring as much liquid out as possible, and then use a paper towel to soak up any remaining liquid from the clump of solids. Next, mix baking soda with the solids; start with 1/4 teaspoon and then add more if necessary to pull the solids together. Make sure you mix the substance well! The end result should have the consistency and appearance of custard or thick vanilla pudding. Now you have a slime made from the polymers in milk protein!
For a different kind of slime, mix white glue (like Elmer’s) with cornstarch and water. (White glue contains polyvinyl alcohol, a polymer.) Use four parts glue to one part cornstarch mixed with one part water: combine the water and cornstarch, and then add the glue gradually, stirring well. You’ll need to let the mixture stand for several minutes before it turns to a solid putty-like slime.
For other fun slime recipes, along with an explanation of the science behind them, consider our Slime Science Kit.
Noteworthy Scientist: Robert Boyle (1627-1691)
Robert Boyle is often called the ‘father of modern chemistry.’ He was born on January 25, 1627, in Ireland, the son of Richard Boyle, the Earl of Cork, who was possibly the richest man in Great Britain. Boyle was the 14th in a family of 15 children, 12 of whom survived childhood. He was educated both at Eton College and by tutors at home, but never attended a university. In 1641 Boyle traveled with his tutor to Italy, and he was still there when Galileo died in 1642. He began to study Galileo’s works, which influenced him greatly and directed him to scientific study.
In 1654, Boyle moved to Oxford where he was a part of the ‘Invisible College,’ a group of scientists that eventually became the Royal Society of London, which is still the oldest continuous scientific society. Boyle’s major scientific contributions included developing the vacuum pump and using it to prove that air is necessary for sound to travel. His most important work was done in the field of chemistry, earning him the name, ‘The Mighty Chemist.’ By publishing detailed accounts of his experiments, including the procedure steps, apparatus and observations, Boyle made a strong case for an empirical approach to science. This means that he tested his theories and derived conclusions from his actual observations. Previously, many scientists had devised theories and tried to prove them with logic alone, rather than using physical experimentation. Because of his strength in experimentation, Boyle is considered one of the pioneers of the scientific method. Among many other things, Boyle’s experiments provided methods for classifying substances by performing acid tests and alkali tests.
In addition to his scientific endeavors, Boyle was a devout Christian. He saw no conflict between religion and science, but rather he appreciated the fact that nature proclaims God’s power. From a desire to bring the gospel to the nations, he promoted and supported efforts to translate the Bible into other languages. In 1680 he was offered the position of president of the Royal Society, but declined because the oaths of office violated his Christian principles.
He lived in London from 1688 until his death in 1691.
Inventions: Vulcanized Rubber
In the early 1830s, America excitedly embraced the new craze—rubber, the wonder water-proof substance made from the sap of tropical rubber trees. The trouble was that the rubber of the time was not suitable for weather extremes. In heat, the rubber melted. In cold, it became hard and brittle. It stuck to everything. Many scientists set to work trying to improve the product. One of these scientists was Charles Goodyear. For years he experimented with adding substances to rubber to make it more durable. In 1839 Goodyear added sulfur to his rubber. He accidentally dropped some of the mixture on a hot stove, and was surprised to see that instead of melting, the rubber changed into a material that was harder and less sticky, while still maintaining elasticity. This kind of rubber was called ‘vulcanized rubber,’ and is now used in many products, including automobile tires. And now you know how the tire company got its name!
Rockin’ Rosin? Rosin, used by gymnasts and violinists, is made from naturally-occurring polymers in pine trees: the pulp from the wood is used to make the rosin.
Rubbin’ Rubber? How did rubber get its name? Over 200 years ago, the scientist Joseph Priestly used a solid substance to rub out his pencil marks. He named it ‘rubber.’
The Scientific Speaker
Polymer comes from the Greek word polumeres, ‘having many parts.’ The prefix poly means ‘many’ and the affix mer, ‘parts.’
Visit the ‘Macrogalleria,’ where you’ll find out more about the how polymers function and how we use them.
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