Who knew that salad dressing holds the secret to getting oil and water to mix? Learn how to make it happen in this “shaky” experiment. (Plus, make delicious salad dressing!)
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The saying goes that oil and water—like cats and dogs or siblings in the back seat of a car—don’t mix. An easy way to see whether the old saying is true is to use oil and vinegar (vinegar is mostly made of water). Use tape and a marker or pen to label 1 jar as “Control.” Measure your first 6 tablespoons oil and 2 tablespoons vinegar into a glass jar. Screw the lid on tightly. What do the vinegar and oil look like in the jar?
But (spoiler!) there is a way to get oil and water to play nicely. You have to turn them into an emulsion (“ih-MUHL-shun”). Emulsion is a science term for a combination of 2 liquids that don’t usually mix, such as oil and water. An emulsion of oil and vinegar is also called a vinaigrette, which is used as a salad dressing or sauce.
There are a few ways to make an emulsion:
Let’s find out which makes a better emulsion: just mixing the liquids really well or adding an emulsifier, too!
Use tape and a marker or pen to label a second jar “Mustard.” Measure the next 6 tablespoons oil, 2 tablespoons vinegar, and the mustard into the jar. Screw the lid on tightly.
Use tape and a marker or pen to label a third jar “Mayonnaise.” Measure remaining 6 tablespoons oil, 2 tablespoons vinegar, and the mayonnaise into the jar. Screw the lid on tightly.
Get your arm muscles ready! Make sure the lids are on tight and then vigorously shake 2 jars, 1 in each hand, for 30 seconds. Set the jars aside. (You can also enlist a friend or family member to help. Have the second person shake the 1 remaining jar at the same time.)
Check that the lid is on tight and then immediately start shaking the remaining jar for 30 seconds. Set the jar aside next to the other 2 jars.
Now it’s time to see how long each emulsion lasts. Set a timer or watch the clock for 15 minutes. After 15 minutes have passed, check on your emulsions.
Continue to observe your jars every 15 minutes, until 1 hour has passed. Have any of the emulsions separated into layers of oil and vinegar again?
Turn your emulsions into a vinaigrette salad dressing by following these steps.
Who knew that the condiments in your refrigerator or on your pantry shelf were the solution to getting oil and water—typically sworn enemies—to become friends? Here’s what our jars looked like after sitting for 15, 30, 45, and 60 minutes:
Here at the America’s Test Kitchen Kids lab, we found that mayonnaise was the best emulsifier of the bunch, with mustard a close second. The mixture that we shook without an emulsifier was almost back to two fully separate layers after 15 minutes.
Without an emulsifier, as soon as you stop mixing or shaking, droplets of oil and vinegar start to find each other again. And you know how much oil loves to hang out with oil and water loves to hang out with water. Pretty quickly, the vinegar and oil separate into two separate layers again.
So, how do the emulsifiers—the mustard and mayonnaise—get water molecules, with their “sticky” positive and negative charges, to snuggle up with oil molecules, which don’t have any charge?
Emulsifiers are molecules that bridge the gap between two substances that don’t typically get along.
Emulsifiers, just like water and oil, are made up of molecules. One end of an emulsifier molecule is attracted to water, and the other end is compatible with oil. Imagine the emulsifier is holding hands with oil on one side and with water on the other side. When we shook the jars, we broke the oil and water up into tiny droplets. The emulsifiers surrounded those tiny droplets and prevented them from sticking together again . . . at least for a while.
When making an emulsion to eat, flavor is important to consider. Since you’re dressing your salad right after you mix (or shake!) your vinaigrette, any of our emulsions will work, so pick the flavor you like best!
Want to learn more about the science of mixing and about emulsions in particular? Check out the podcast we did in collaboration with Brains On!