Homemade Ice Cream – Sick Science!
Use science know-how to create a tasty vanilla treat!
Legend has it that the Roman emperor, Nero, is credited as the first person to make ice cream. Nero commanded slaves to bring snow down from the mountains, which was then used to freeze the flavored cream mixture. The secret was to lower the freezing point of ice in order to freeze the cream. How? The scientific secret is salt! Here’s a scientific recipe that you can use at home to make your own ice cream.
- Large (1 gallon) plastic jar (a coffee can works, too)
- 2 quart-size zipper-lock bags
- Half & Half
- Crushed ice (or snow in the winter!)
- Rock salt
- Towel (or winter gloves)
- Fill the plastic jar about half full with crushed ice.
- Add about 6 tablespoons of rock salt to the ice. Seal the plastic jar and shake the ice and salt for about five minutes. You’ll need to wear your gloves when you’re handling the jar. If you’re curious as to why you have to wear gloves, measure the temperature of the mixture with a thermometer. The rock salt and ice mixture gets down to about 14 degrees F (-10 degrees C)!
Use one quart-size zipper-lock bag to mix the following ingredients:
- 1/2 cup of Half & Half
- 1 tablespoon sugar
- 1/2 teaspoon vanilla extract
- Seal tightly, allowing as little air to remain in the bag as possible. Too much air left inside may force the bag open during shaking.
- Place this bag inside the other quart-size bag, again leaving as little air inside as possible and sealing well. By double-bagging, the risk of salt and ice leaking into the ice cream is minimized.
- Place the two bags inside the jar with the ice and seal the bag. Wrap the bag in the towel or put your gloves on. Shake, rock, roll, and mix that can! Your ice cream should be ready after about 15-20 minutes.
- Once mixed, remove the inner bags from the jar and rinse them well with water. You don’t want any salt water accidentally getting into your ice cream.
How Does It Work?
What does the salt do?
Just like we use salt on icy roads in the winter, salt mixed with ice in this case also causes the ice to melt. When salt comes into contact with ice, the freezing point of the ice is lowered. The lowering of the freezing point depends on the amount of salt added. The more salt added, the lower the temperature will be before the salt-water solution freezes. For example, water will normally freeze at 32 degrees F. A 10% salt solution freezes at 20 degrees F, and a 20% solution freezes at 2 degrees F. When salt is added to the ice (or snow), some of the ice melts because the freezing point is lowered. Always remember that heat must be absorbed by the ice for it to melt. The heat that causes the melting comes from the surroundings (the warmer cream mixture). By lowering the temperature at which ice is frozen, you were able to create an environment in which the cream mixture could freeze at a temperature below 32 degrees F into ice cream.
Did You Know? In 1846, Nancy Johnson invented the hand-cranked ice cream churn and ice cream surged in popularity. Then, in 1904, ice cream cones were invented at the St. Louis World Exposition. An ice cream vendor ran out of dishes and improvised by rolling up some waffles to make cones.