Freezing Point Depression Ice Cream
Chill out! The Science of Freezing
You know that ice makes things cold. But to make ice cream freeze really fast, we need to get the ice even colder. Adding salt to ice lowers its freezing point. This means the ice will melt at a temperature below 0°C (32°F), drawing heat away from our ice cream mixture even faster and freezing it quickly. This is called freezing point depression – a key concept in chemistry and physics!
Ingredients:
- Approximately 1/2 cup of Half-and-Half
- 1 tablespoon of Sugar
- 1/4 teaspoon of Vanilla Extract
- About 1/2 cup of Salt
- Plenty of Ice Cubes
- 1 Quart-sized Ziploc Bag
- 1 Gallon-sized Ziploc Bag
- Spoon for eating!
Instructions:
- Mix Your Sweet Base: Take your quart-sized Ziploc bag. Carefully measure and pour in your Milk (or Half-and-Half/Cream), Sugar, and Vanilla Extract.
- Seal it TIGHT! This is super important! Gently squeeze out as much air as you can from the quart bag before sealing it completely. Make sure the seal is really closed along the entire top. You might even want to double-check it or ask a facilitator to help you seal it extra securely. You don’t want salt water getting into your ice cream mixture!
- Prepare the Freezing Chamber: Now, take your gallon-sized Ziploc bag. Fill it about one-third to halfway full with ice cubes.
- Add the Magic (Salt!): Measure your Salt (about 1/2 cup) and add it directly into the gallon bag with the ice.
- Combine the Bags: Place your securely sealed quart bag (the one with your liquid ice cream mix) inside the gallon bag with the ice and salt.
- Seal the Outer Bag: Just like with the inner bag, squeeze out some of the excess air from the gallon bag and seal it tightly. Double-check that seal too!
- Shake, Shake, Shake! Now for the fun part! Grab the sealed gallon bag and start shaking, squishing, and massaging it constantly. The salt is lowering the temperature of the melting ice, making it cold enough to freeze your mixture. Keep shaking for about 5 to 10 minutes.
- Feel the Change: As you shake, you should start to feel the liquid in the inner bag thickening and freezing into ice cream! Keep going until it feels like soft-serve ice cream.
- Rinse and Reveal: Once your ice cream is frozen, carefully take the small quart bag out of the larger gallon bag. You might want to quickly rinse the outside of the quart bag under cold water to get any salt residue off before opening it.
- Open and Enjoy! Open your quart bag, grab a spoon, and enjoy the delicious ice cream you made using the power of science!
Science Reminder: Adding salt to the ice lowers its freezing point. This makes the ice melt at a temperature below (), creating a super-cold slushy mixture that quickly pulls heat away from your ice cream ingredients, causing them to freez