Ice Cream in a Bag for kids | Kidstir (2024)

FAQs

What is the science behind ice cream in a bag for kids? ›

Add salt and the freezing point drops by a few degrees. When you add salt to the ice in the outer bag, the ice (at 0°C) is now above its freezing point – so it begins to melt. Melting requires energy, and in this case that energy comes from the flavoured milk mixture in the inner bag.

The two-bag method works because of the combination of salt and ice. Salt causes the ice in the bag to melt at a lower temperature than usual (if you've sprinkled salt on an icy sidewalk, you know the drill), keeping everything much colder for longer.

This is an example of an exothermic reaction . An exothermic reaction is a chemical reaction that releases light or heat, otherwise known as energy . In this case, heat is released from molecules moving around, freezing cream into ice cream! More exothermic reactions include the burning of materials and explosions.

Ice cream is an emulsion—a combination of two liquids that don't normally mix together. Instead, one of the liquids is dispersed throughout the other. In ice cream, liquid particles of fat—called fat globules—are spread throughout a mixture of water, sugar, and ice, along with air bubbles (Fig. 1).

In a Plastic Bag

In a small plastic bag, add ½ cup heavy cream, ½ cup milk, 2 tablespoons fine sugar and ½ teaspoon vanilla extract. In another larger bag, add 2 to 3 cups ice and ¼ cup salt, then place the smaller bag inside and seal it. Shake the big bag for about 6 to 8 minutes, and presto! Instant ice cream.

Salt: Rock salt, which is also sometimes labeled as "ice cream salt", works best for lowering the temperature of the ice to freeze the ice cream quickly. But coarse kosher salt or even regular table salt will work in a pinch if that's what you have on hand.

Rock salt helps slow the melting rate of ice. In fact, rock salt was used for making old-fashioned ice cream! Scatter a handful or two of rock salt directly on top of the ice. Put the ice cream in freezer bags inside the cooler for added insulation.

Why does putting ice cream in a bag keep it soft? ›

Similar to how a winter coat can help buffer against cold air, a plastic bag acts as an insulator in the freezer. The cold must penetrate the bag, the air within it, and then the carton itself before finally affecting the ice cream. The plastic bag layer helps keep the ice cream soft and easily scoopable.

Instant Ice Science Explained

When ice freezes, the water forms small crystals that gradually spread. If you catch the cold water before the crystals have time to form, you can still pour out the water and it will freeze as you pour. Pouring it over an ice cube triggers crystals to form faster than they normally would.

Shaking the bag while this heat transfer is happening also helps by adding air to the ice cream, which lightens the texture so the ice cream is nice and creamy.