Thanksgiving Science

Thanksgiving is all about the food and being together with family. In turn, cooking has everything to do with chemistry and physics: heating and cooling ingredients, mixing, changing liquids into solids, interactions between different types of matter. These are all things that a scientist might investigate, and you and your kids can too. It’s a great time to get into the kitchen to do some easy science experiments!  

Here are two experiments that will get your kids thinking about a couple of the foods they eat on Thanksgiving Day: cranberries and potatoes. 

Cranberries have some fascinating properties and are fun to explore with kids. Grab a handful of fresh cranberries and examine them (if you have a magnifying glass or hand-lens you can really get up close and personal with these little berries). You might even want to have your kids weigh and measure them. Carefully cut one open and observe their insides. You will see they are filled with air pockets (which is ideal because the farmers who grow them flood their cranberry bogs in order to harvest them). Have the kids experiment with these and other berries to see which ones sink and which ones float in a pan of water. Homemade cranberry juice makes a great ph indicator. Contact me for the recipe and how to proceed with that experiment! 

With your close supervision, kids will love making cranberry sauce and learning about the science behind it. Please use caution, as cranberries will pop when they hit the hot water. 

 Cranberry Sauce Science (by Kristen May)

 Materials:

• 4 cups of cranberries (approximately one 16-ounce bag)
• 2 cups sugar
• 1-1/2 cups water
• Deep saucepan
• Long handled spoon

 What You Do:

1. First, wash and pick over your cranberries.
2. Mix the sugar and water in your saucepan, and bring the mixture to a boil. Cook over medium heat until the sugar has completely melted, and the solution is clear. (Psst: this is an example of crystalline sugar dissolving into water to form a solution).
3. Now add the cranberries all at once, and turn your burner heat up to high. Invite your child to look at the mix and stir with you, while taking care that his face isn’t too close to the mixture, which can spatter. At first, the cranberries will float and bob. Within a few minutes, however, you’ll watch them start to pop open and turn the whole mixture bright red.
4. Keep stirring as the mixture cooks. Quite quickly—within 5-10 minutes on most stovetops—you’ll feel the whole batch thicken substantially. Take it off the heat, stir a little more, and then pour it into glass jars or a pyrex storage container which have either been run through a very hot dishwasher or sterilized in boiling water. Let it cool…and watch it thicken some more. Store in the fridge for up to two weeks before serving, or just enjoy right away!

What’s Going On

When they first made cranberry sauce, our colonial ancestors were actually taking advantage of a natural substance called pectin, which is found in the cell walls of fruit, especially their rinds. When high-pectin fruits (this also includes some grapes and apples, as well as cranberries) are cooked with sugar and water and sometimes a bit of citric acid, the pectin molecules separate from the fruit cells and reconfigure to form a stiff network of complex carbohydrates. This is the jell that we feel when we stick a spoon into a jam pot…or a dish of cranberry jam.

Note: it is possible to “goof” with this experiment. First, make sure you follow the recipe and add the amounts of sugar and water that are required. If the balance isn’t right, the network made by pectin molecules may not come together properly. You can still have a tasty sauce, but it won’t be firmly jelled!

The following potato experiment was adapted from the North Carolina State University “Science Junction” website. Please use care when slicing your potatoes! 

Floating Potato

Background Questions

• Why do some things float?
• What is density and does it have anything to do with controlling what floats?
• What is solubility?
• How soluble are salt or sugar in water?

 Materials

• Water
• Potato slices, 3 about 1/4 inch slices
• 3 clear cups or glasses, tall and skinny will be the most dramatic
• Stir rod or spoon
• Salt 
• food coloring

 What You Do

Your goal is to make one of the potato slices sink, one of the slices float, and one of the slices be suspended right in the middle of the glass!

1. Cut your potato slices out of a raw potato.
2. Fill one of the glasses about three-fourths full with water and put in a potato slice. What happened?
3. Now add the same amount of water and different amounts of salt to the two remaining glasses. Your goal is to make one of the slices float and one of them be suspended half way down the glass that you are using.

 Thinking about it

• What was different about the three glasses that allowed the potatoes to float or sink?
• Why didn't the water spill out the top of the glass when you added the salt?

 Extension

• Take a little bit of water and add a drop of food coloring.
• Very carefully, so that it doesn't mix, add that water to the top of the glass with the potato that is floating. What happened?
• What does that tell you about the two kinds of water in the glass?

 Happy experimenting everyone, and have a safe and joyous Thanksgiving!