Ice cream is a deceptively complex mixture. One would think it’s roughly what’s in the name — frozen cream.
While that may have been true in the days before freezers, deeper understandings of chemistry have turned the process of making ice cream into a science.
There are six basic components to ice cream: air, ice crystals, sweeteners, fat, solids, and an emulsifier like egg yolk or xanthan gum. When combined properly, these ingredients can create the perfect bowl of ice cream. But how?
The fat, usually cream or butter, is what gives ice creams its flavor and structure.
Fat doesn’t naturally combine smoothly with any water-based syrups, and without the smoothness, air can’t get trapped inside the mixture, preventing it from gaining its distinctively rich texture.
Emulsifiers allow the fat to blend with the water-based ingredients.
Just as soap combines oil and water through its hydrophobic and hydrophilic ends, egg yolks do the same thing for fats and sugars in ice cream. Many of the compounds contained in egg yolks have the same emulsifying effects as soap.
And, of course, ice cream isn’t very icey without ice crystals.
The size of the crystals contributes to the texture of the dessert.
Anyone who’s eaten freezer-burnt ice cream knows that large ice crystals aren’t the chunks advertised in “Chunky Monkey.” When ice cream is frozen, the key objective is to keep ice crystals small.
This is achieved in one of two ways: either by freezing the ice cream very slowly while keeping it in constant motion or by freezing it instantly.
Ice cream machines work by slowly removing heat from the ice cream as it churns the liquid, reducing the chances of large ice crystals forming.
Using liquid nitrogen to instantly freeze ice cream reduces the likelihood of the formation of large crystals.
Since liquid nitrogen is can be difficult to acquire, there’s a more accessible way to make ice cream by supercooling it: rock salt.
Rock salt lowers the freezing point of water, allowing ice cream to freeze faster than in a mixer. Making homemade ice cream with rock salt is simple, affordable and fun.
This basic ice cream recipe is not going to yield ice cream your favorite Ben and Jerry’s flavor, but it is a tasty way to kill an hour between class and work.
To make rock salt ice cream, you need ice, rock salt, a cup of whole milk, cream or half and half, a teaspoon of vanilla extract and two tablespoons of granulated sugar. You also need either a sandwich bag and gallon bag or two clean coffee cans— where one fits inside the other with plenty of space.
In the smaller container, mix the milk base, vanilla, sugar and syrups or candies, and seal the container. Then, place the smaller bag or can inside of the larger one, and begin packing ice around the milk mixture. For best results, alternate packing ice and salt. Once the larger container is full, seal it and prepare for approximately 30 minutes of mild entertainment. Winter gloves are recommended at this point.
Either roll the bag (or can) around or find a friend to help, but keep the ice cream moving. After 30-minutes, there should be a frozen, if a bit salty, treat ready in the container.
Since July is National Ice Cream Month, why not kill some time with a delicious project? It’s a great way to deal with the stifling July heat.