When lava comes out of the earth, it is hot and liquid. Once it is out in the open air, it cools down and becomes solid. It might cool down quickly or slowly, and it might sit undisturbed or move around a lot. Let’s see what happens when something hot and liquid cools down in different ways, by making fudge!
This is an adaptation of an activity by the exploratorium, see here for more info.
Materials: (Don’t be afraid to substitute if you don’t have something – see how it turns out!)
- 3 ounces unsweetened chocolate
- 21 ounces (3 cups) sugar
- 1 cup half and half
- 1 tablespoon corn syrup
- 1/4 teaspoon salt
- 3 tablespoons butter
- 2 teaspoons vanilla
- kitchen thermometer (candy or digital)
- stove
- large pot (ideally heavy)
- wooden spoon or similar
- pastry brush (optional)
- containers (glass is best)
Here are the directions. You don’t have to follow these exactly – science is about trying new things and seeing what happens! But make sure you write down what you do differently. You can also compare two things (scientists call that a variable). The variable in the directions below is whether you stir the mixture at the end or not. How do you think stirring will affect the final product?
- Mix chocolate, sugar, half and half, corn syrup, and salt in the pot, and heat on medium. Stir with the spoon until the chocolate melts and the mixture begins to boil.
- As soon as the syrup starts to boil, stop stirring and attach the thermometer to the side of the saucepan, being careful not to let it touch the bottom.
- Let the syrup cook, undisturbed, until it reaches the soft-ball stage, about 235° F–240° F. While it cooks, wash down the sides of the saucepan with a pastry brush dipped in a small amount of warm water to loosen and dissolve any sugar crystals clinging to the sides.
- Turn off the heat and let the mixture rest, undisturbed. Let it cool to approximately 110° F.
- Add the butter and vanilla and stir briefly with a wooden spoon to combine. Then take a scoop (about 1 cup) out and put it into a container. Don’t touch it again until it is solid!
- Stir the remaining mixture until it gets really difficult, and the fudge gets dull and lightens in color, about 15 minutes. Then move it to another container.
- Once the fudge in both containers has totally set, compare them by looking, touching, and tasting. How are they the same? How are they different?
