Happy Thanksgiving! Just a few days ago, most of the country was celebrating Thanksgiving by having a turkey dinner. Traditionally, Thanksgiving dinners aren’t complete without mashed potatoes and gravy, but gravy is notoriously tricky to thicken to the right consistency. So how exactly do you make gravy, anyway? Let’s find out!
Some people swear by adding flour to the turkey drippings, while some say that the addition of corn starch is the secret to perfect gravy. The truth is, either ingredient will work to thicken gravy because both corn starch and flour contain starch, which is the one necessary ingredient to thickening a liquid such as gravy.
How does starch work? http://www.thekitchn.com/food-science-how-starch-thicke-83665
Starch will thicken a liquid, but the catalyst for starch to thicken is heat (Remember, a catalyst is a helper that gets a reaction going). When heat is applied, starch grains take in liquid and swell, causing that liquid to become thicker. Without heat, starch grains won’t take in enough liquid to make a difference.
Try to make your own gravy! What works better, flour or corn starch? Predict which ingredient will thicken the water quickest. You don’t have to go to the trouble of making real gravy to test out these ingredients. Just use warm water, and you’ll get a similar effect.
YOU WILL NEED:
- Two mugs or small bowls
- Corn starch
Here’s what to do:
- Put 1/2 cup of water in each mug.
- Microwave both mugs of water for about 1 minute (the water should be warm, not boiling).
- Add 1 tablespoon of corn starch to the mug on the left, and 1 tablespoon of flour to the mug on the right.
- Stir both mugs. Did the consistency change?
- Keep adding flour and corn starch 1 tablespoon at a time, stirring after each spoonful. How many tablespoons of corn starch does it take for the liquid to get noticeably thicker? How many tablespoons of flour does it take?
- You should have noticed that it took way more flour (about twice as much) to get the same thickness as the mug with corn starch. This is because corn starch is 100% starch, but flour is a mix of starch and protein.
If you continue to add starch to water, you’ll get a gooey substance that’s fun to play with. You can roll the starchy goop into a ball, but when you quit moving it will slip through your fingers like liquid!
If you’re looking for some messy fun, try out the first slime recipe in our blog: http://discoveryexpress.weebly.com/blog/two-times-the-slime-fun-with-polymers (you can continue to use corn starch instead of liquid starch).
If you want to try to make your own gravy, here’s a recipe to test out: http://saucepankids.com/index.php/2012/07/real-gravy-no-bisto-recipe/
Now that you know a little bit about starch and its properties, lets move on to our next activity.
A few weeks ago, we did an activity called Iodine Clock Reaction.
If you missed it, check it out here: http://discoveryexpress.weebly.com/blog/iodine-clock-reaction
In that activity, we combined iodine, starch, vitamin C, and hydrogen peroxide. Because of a chemical reaction, clear liquids suddenly became dark blue! In our activity today, we will use iodine to test certain substances for starch. If the substance contains starch, BINGO! the iodine will turn blue.
YOU WILL NEED:
- Iodine tincture (http://www.amazon.com/Cumberland-Swan-Iodine/dp/B00I3LNFT6)
- Plastic cup
- Polystyrene (styrofoam) cup
Here’s what to do!
- Create a work space where you can get messy. Either grab a large tray or cover your space with plastic or newspaper. This will be your testing area.
- Dilute the iodine with water. The ratio of iodine to water should be 1:10. (For example, you could use 1 tablespoon of iodine and 10 tablespoons of water). If you need help, ask an adult!
- Create a chart of substances that you will test for starch. You are going to test a plastic cup, styrofoam cup, apple slice, potato slice, piece of bread, paper, and tissue. If you want to test even more, add them to your chart. Then predict whether you think each substance has starch in it. Leave your final column blank to record your test results. Your chart may look something like this:
5. Fill your dropper with iodine solution.
6. Place your first substance in your testing area. Squeeze a drop of iodine solution onto your first substance and observe. Did the iodine change colors? If not, the substance does not have starch. If the iodine changed to a dark blue, the substance must have starch! Fill in your chart after you test each material.
7. After your testing is over, record your final observations. Were your predictions right? Were you surprised by your results?