The Science of Stretchy Cheese

Don’t use low-fat or preshredded cheese here. You can swap Monterey Jack, Swiss, or even mild or sharp cheddar for the extra-sharp cheddar.

1. Place bread slices on cutting board. Sprinkle cheddar evenly over 1 slice of bread. Sprinkle mozzarella evenly over second slice of bread. Place 1 bread slice on top of each sandwich and press down gently.

2. In 12-inch nonstick skillet, melt butter over medium-low heat, swirling to evenly coat skillet, about 1 minute. 

3. Place sandwiches in skillet and press down on them lightly with spatula. Cook sandwiches until first side is golden brown, 3 to 5 minutes.

4. Use spatula to flip sandwiches and press lightly again. Cook until second side is golden brown and cheese is melted, about 2 minutes.

5. Turn off heat. Use spatula to transfer sandwiches back to cutting board. Let cool for 2 minutes.

6. While sandwiches cool, make a prediction: Which cheese do you think will stretch more when you pull apart your sandwiches: cheddar or mozzarella?

7. Observe your results: Use your hands to gently break cheddar sandwich in half. Hold left half of sandwich still in your left hand. Use your right hand to gently pull other half of sandwich to the right. Stop pulling once cheese breaks and is no longer connecting 2 halves of sandwich.

8. Repeat test with mozzarella sandwich.

9. Eat your experiment: Share your grilled cheese sandwiches with a friend or family member!

Did the mozzarella cheese stretch much farther than the cheddar cheese? We were able to stretch our mozzarella grilled cheese 33 inches! That’s about the distance from one hand to the other when your arms are stretched out wide.

Why is mozzarella cheese so good at stretching? It has a lot to do with the way mozzarella is made. Adding acid or enzymes to milk starts the cheese-making process—it causes the milk to separate into solid curds and liquid whey. Those curds eventually get smooshed together into cheese.

To make mozzarella, the curds are then stretched and pulled over and over again. During the stretching and pulling, proteins (molecules in the cheese) make their way into very straight lines. When mozzarella is heated, those straight lines of protein loosen up and you can pull them into long strings. Many cheeses, like cheddar, aren’t stretched after their curds are pressed together. This means that their proteins don’t form straight lines. When these cheeses melt, their proteins flow in lots of different directions, so the cheese doesn’t stretch as much.