Science, Tech, Math › Science How to Make Ice Cream in a Bag A Delicious Experiment With Freezing Point Depression Share Flipboard Email Print BRETT STEVENS/Getty Images Science Chemistry Projects & Experiments Basics Chemical Laws Molecules Periodic Table Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated November 28, 2019 You can make ice cream in a plastic bag as a fun science project. The best part is you don't need an ice cream maker or even a freezer. This is a fun and tasty food science project that explores freezing point depression. Materials 1/4 cup sugar1/2 cup milk1/2 cup whipping cream (heavy cream)1/4 teaspoon vanilla or vanilla flavoring (vanillin)1 (quart) zipper-top baggie1 (gallon) zipper-top baggie2 cups iceThermometer1/2 to 3/4 cup sodium chloride (NaCl) as table salt or rock saltMeasuring cups and spoonsCups and spoons for eating your treat Procedure Add 1/4 cup sugar, 1/2 cup milk, 1/2 cup whipping cream, and 1/4 teaspoon vanilla to the quart zipper bag. Seal the bag securely.Put 2 cups of ice into the gallon plastic bag.Use a thermometer to measure and record the temperature of the ice in the gallon bag.Add 1/2 to 3/4 cup salt (sodium chloride) to the bag of ice.Place the sealed quart bag inside the gallon bag of ice and salt. Seal the gallon bag securely.Gently rock the gallon bag from side to side. It's best to hold it by the top seal or to have gloves or a cloth between the bag and your hands because the bag will be cold enough to damage your skin.Continue to rock the bag for 10-15 minutes or until the contents of the quart bag have solidified into ice cream.Open the gallon bag and use the thermometer to measure and record the temperature of the ice/salt mixture.Remove the quart bag, open it, serve the contents into cups with spoons. How It Works Ice has to absorb energy to melt, changing the phase of water from a solid to a liquid. When you use ice to cool the ingredients for ice cream, the energy is absorbed from the ingredients and from the outside environment (like your hands, if you are holding the baggie of ice.) When you add salt, it lowers the freezing point of the ice, so even more energy has to be absorbed from the environment for the ice to melt. This makes the ice colder than it was before, which is how your ice cream freezes. Ideally, you would make your ice cream using "ice cream salt," which is just salt sold as large crystals instead of the small crystals in table salt. The larger crystals take more time to dissolve in the water around the ice, which allows for more even cooling of the ice cream. Other Types of Salt You could use other types of salt instead of sodium chloride, but you couldn't substitute sugar for the salt because (a) sugar doesn't dissolve well in cold water and (b) sugar doesn't dissolve into multiple particles, like an ionic material such as salt. Compounds that break into two pieces upon dissolving, like NaCl breaks into Na+ and Cl-, are better at lowering the freezing point than substances that don't separate into particles because the added particles disrupt the ability of the water to form crystalline ice. The more particles there are, the greater the disruption and the greater the impact on particle-dependent properties (colligative properties) like freezing point depression, boiling point elevation, and osmotic pressure. The salt causes the ice to absorb more energy from the environment (becoming colder), so although it lowers the point at which water will re-freeze into ice, you can't add salt to very cold ice and expect it to freeze your ice cream or de-ice a snowy sidewalk. (Water has to be present.) This is why NaCl isn't used to de-ice sidewalks in areas that are very cold.