Ice Cream Preparation
You can use store-bought ice cream, but it's more fun to make your own. Ice cream production relies on the fact that adding a non-volatile solute to a solvent lowers the freezing point of the solvent:
Tf(solution) = Tf(solvent) – mKfi
Kf = cryoscopic constant for the solvent
i = van't Hoff factor
For ice cream, the addition of salt to ice lowers the freezing point of water. Along with constant mixing, the cold freezes the cream/milk/sugar/flavor blend into a creamy frozen treat.
1. Combine half & half, sugar, cocoa, and vanilla in a quart-sized, zippered plastic bag. Seal tightly and place inside another bag. Seal the second bag tightly.
2. Place inside a gallon-sized zippered bag or large, watertight container. (If using plastic bag, be sure to double-bag.) Add ice and salt.
3. Wrap container in a towel and/or wear gloves, and gently shake for 20 minutes.
4. Carefully remove the smaller bags. The milk mixture will now be a soft-serve ice cream. To use in the van't Hoff Factor Koffie Ijsje, transfer the ice cream to a freezer-safe container and freeze for 1 hour or until firm.