Carl's Corner:
Ice Cream Chemistry
by: Carl Antholz

As I matured and learned more about the world, I realize that I still want to make ice cream. A culinary adventure is born – how does one make their own ice cream?

Unlikely as it seems, the technology required to make ice cream probably originated in the Arabian dessert a few thousand years pre-gelato. This is where it was discovered that salt lowers the freezing temperature of water. When you add salt to the ice, it lowers the freezing point of the ice, so more energy has to be absorbed from the environment in order for the ice to melt. By lowering the temperature at which ice is frozen, we are able to create an environment where a milk or cream mixture can freeze at a temperature below 32 degrees F into ice cream. Sugar, including the lactose from the milk or cream, also contributes to a lowered freezing point so that the ice cream still contains some unfrozen water at the very low temperature typical of their serving temperatures of between 15 and –18 degrees C. Without this unfrozen water, the ice cream would be too hard to scoop. Whew, chemistry, I know, but it’s dire to the process of making delicious homemade ice cream.

In addition to cream, sugar, and enhanced chilling methods, two other interlinked elements are necessary to make basic ice cream. Air has to be incorporated to produce the desired density, and stirring is required to produce the desired texture (smooth and creamy instead of crystallized and icy). Fortunately, this is done as a single action, much like folding fluffy egg whites (that would be the air) into dense batter (that would be the sweetened cream), and stopping when the desired texture is achieved. And, that’s all there is to it, right?

Nope!

Leave it to the Italians and the French to turn basic creamed ice into an American craving. They discovered the benefits of stirring the mix in the 1600s, and they each decided to not leave well enough alone.

“It’s got to be better than this simple combination of cream and sugar. Let’s freeze an egg custard!” A few decades before Waterloo, the French had discovered that frequent stirring of the egg yolk-loaded mix gave a finer, less crystalline texture. Imagine Napoleon’s delight! He may have even taken his hand out of his shirt to take a taste.

While the French were adding eggs to the mix, the Italians were still scooping up ice from their local mountains and transforming it into basic, bland gelato, when they also had a great idea. I picture it going something like this. An unsteady but eager young child was toddling toward the collected ice and tipped over a vial of rose water onto it. Oh no, they cried, you’ve ruined the “ice cream.” Not a culture to waste, they tried it anyway, and lo and behold, it was better than ever! Said toddler got an extra helping that night because she had made a wonderful discovery: you can add flavorings to ice cream!

FLAVORED ICE CREAM!

If you want flavored ice cream (and who doesn’t), here’s where the chemistry gets really interesting. Adding vanilla extract or vanilla from a scraped vanilla bean can lead to two different textures. High quality vanilla extract contains at least 36% alcohol and vanilla scraped from the bean contains none. Alcohol retards the freezing process dramatically, leading to a softer ice cream, while the bean’s vanilla will yield the truest consistency. Neither is better nor worse, as it’s just a matter of taste and availability. There’s no such problem with high-quality chocolate. It will melt into most cream/custard mixes smoothly.

Adding whole fruit for flavoring brings up an old set of physical problems:

• Unless blueberries are slightly mushed before freezing, they’ll become marbles.
• Unless strawberries are cut into 1/8th segments, they’ll become large rock hard clutter.
• Unless peaches are cut into medium dice, they’ll become large rock hard clutter.

Adding whole, slightly mashed fruit to lightly cooked basic custard (including a puree of said fruit) is the best way to add pure fruit flavor to high quality ice cream. This way, the flavor mixes throughout instead of leaving you with hard chunks swimming around.

While you can create ice cream with simply a small bowl with cream nestled into a larger bowl containing salted ice and some serious stirring, I wouldn’t recommend it. You will receive much better results with an ice cream maker, not only because all the “bowls” fit together perfectly, but also because you actually want to be able to use your arms to eat the homemade treat when it’s ready!