van't Hoff Factor Koffie Ijsje


Simple coffee and ice cream belies the complexity of the freezing point depression required to make the ice cream.



1 scoop favorite ice cream
1 cup hot coffee
chocolate or caramel syrup (optional)


1. Put ice cream in a mug.
(If using van't Hoff Factor Ijsje, see recipe below.)
2. Pour coffee over ice cream.
3. Top with chocolate or caramel syrup.

van't Hoff Factor Ijsje Ingredients

1 cup half & half (or 2/3 cup heavy cream, plus 1/3 cup 2% milk)
2 tablespoons sugar
2 tablespoons unsweetened cocoa (optional)
1 teaspoon vanilla extract
6 cups ice
5 tablespoons kosher salt (rock salt or table salt may also be used)

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.

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