The following post is from Shaina of Food for My Family: Food Science Camp: Ice Cream in a Bag
Summer is officially underway!
The first week was exciting, the second was filled with camp and plenty of activities for the younger kids while their sister was away, and the last was summer. Hot and sticky days are stuck at home, where I try to instill the importance of cleanliness and daily chores in the midst of meeting deadlines.
In an attempt to bridge the gap of time between now and the next outing, adventure, or scheduled summer activity, the kids and I are having weekly food science camps. We’ve churned our own butter, and today we’re making ice cream. With our hands. Outside. In 90-degree heat. It’s always a party here.
Ice Cream in a Bag
3/4 cup cream
1/2 cup milk
1/4 cup sugar
1/4 teaspoon vanilla
1 quart-sized zip-top bag
1 gallon-sized zip-top bag
1/2 cup rock salt
3 cups ice
gloves or towel for mixing
Add the cream, milk, sugar, and vanilla to the quart-sized bag and squish to mix, sealing tightly. Add ice and rock salt to the gallon-sized bag and place the quart-sized bag inside it. Seal and shake the gallon-sized bag with one hand below it and one hand holding the top, rocking it back and forth quickly. Use gloves or a cloth to hold the bag.
Shake for 10-15 minutes until the ice cream is stiff. Remove the small bag from the larger one. Carefully open the bag to avoid letting the salt water drip in, and scoop out frozen ice cream. Have your kids take the rock salt and ice temperature to see just how cold it was as you enjoy your bowl of ice cream.
Makes 2 small servings.
The Science Lesson
Why do we need salt? Ice alone will not cause your liquid ice cream mixture to freeze. If you tried that, you would end up with a bag of cool water and a bag of soupy ice cream because as the ice cooled the mixture, its own temperature would increase above freezing, melting the ice.
By adding salt, you are lowering the freezing point of water, which allows it to absorb more energy (heat) from the ice cream liquid, and its final temperature will be much lower than 32º F (or 0º C for you metric folk). This causes the ice cream mixture, which does not have any salt in it, to freeze as the salt and ice melt.
Is salt the only substance that will work? No solute (dissolved particles) will lower the freezing point of water. The reason is that when other molecules are introduced to water, they interfere with water’s ability to solidify at 32º, thus resulting in a lower freezing point.
Salt is the most commonly used because its chemical structure allows it to rapidly dissolve in cold water, causing it to be more effective.
What are you doing during the long days of summer to keep your kid’s bodies and minds working and to help keep you sane? Do you have any fun activities planned for the days you’re spending at home?
|Shaina Olmanson is the freelance writer, photographer, and home cook behind Food for My Family. Cooking daily with and for her four kids and husband, Ole, drives her desire to inspire other families to do the same. Shaina is also the author of Desserts in Jars and regularly contributes to various online sites and traditional print magazines.