The Science of Ice Cream


THE SCIENCE OF ICE CREAM

We fell in love with European ice cream – dense and creamy, with elegant flavors. It was like nothing we could get back home. So, we researched the science and technique for making ice cream and learned how to make it ourselves. The key to the best flavor was to use the best quality, most flavorful ingredients. But the secret to keeping it smooth and creamy was a combination of ingredients and technique.

There is more to ice cream than just freezing quality ingredients. The key is making it smooth and creamy. This is actually more difficult than it seems. Ice cream stays smooth while it is being churned, but then it is put in the freezer in order to harden, and that’s when ice crystals form, ruining the smoothness.

There is a lot of science to keeping it smooth. Making ice cream requires a method and ingredients that prevent large ice crystals from forming. The method is accomplished with a properly designed ice cream maker that keeps all of the mixture moving, and freezes it quickly. The other key is using certain ingredients that keep the ice crystals small. Cultured cream, eggs, invert sugar and alcohol are the keys to keeping the ice crystals small and the mixture creamy.


INGREDIENTS

Creme fraiche is cultured cream, like sour cream, but with a much milder taste. The culture in it prevents ice crystals from forming once the ice cream has been churned and is hardening. We make creme fraiche in an Instant Pot from Horizon cream, which makes this an eco-friendly swap as well, since Horizon is taking action on climate change.

CREME FRAICHE
Check out this recipe

Eggs increase the fat and protein in the mixture. The eggs are raw when whipped with the sugar, but are cooked when the hot cream is slowly added. It is important to bring the mixture to a safe temperature (160 degrees F., according to the USDA). This method will do that without having to go through the added steps of making a custard and risking over cooking the eggs. French ice cream is made with a custard, which requires cooking and tempering, so this method is much easier. Heating the eggs will also denature the protein in the eggs and prohibit ice growth.

Invert sugar, like corn syrup lowers the freezing point of water, making the ice crystals smaller and the ice cream smoother. Corn syrup is NOT the same as high-fructose corn syrup. Honey, and some syrups are partially invert sugars and will do the same thing, to some extent, so we use these for certain flavors. However, honey and syrup will add a lot of flavor.

Sugar lowers the freezing point. The sugar molecules interfere with the water molecules becoming organized into a solid as it freezes.

Alcohol lowers the freezing point, making the ice crystals small. It also keeps ice crystals from forming as the ice cream hardens. Too much, however, and the ice cream won’t freeze. Use one tablespoon of an 80 proof alcohol, and adjust the amount for liqueur that contain more or less alcohol.

Air softens the ice cream and provides insulation allowing the flavors to be tasted even though the ice cream is cold. The air is added continuously as the ice cream is churned.


THE ICE CREAM MAKER

Making ice cream also requires a method that prevents the cream from freezing solid. The mixture must be constantly churned in an ice cream maker to add air and to keep the ice crystals small, so the ice cream stays creamy. When selecting an ice cream maker, the important thing is that it keeps all of the mixture moving, and freezes it quickly. There should be very little space between the paddle and the walls of the container, and the paddle should be designed to turn over the mixture as it rotates. If there is a gap allowing too much ice cream to build up on the container walls it will cause ice formation. The temperature must be cold enough to freeze the mixture quickly, before ice forms.

We use a Whynter Ice Cream maker (model ICM-200LS) which does an excellent job of freezing it quickly. It doesn’t require ice and rock salt or freezing the insert, so it is really easy and convenient. It has a capacity of 2 Quarts, but we found the ice cream is better when we make 1 Quart, so our recipe makes 1 Quart.

Whynter ice cream maker
Whynter ice cream maker

TIPS: It also helps if everything is cold. Make the mixture and thoroughly chill it down to 45 degrees F. Before putting it in the ice cream maker. Making it the day before will ensure that it is thoroughly chilled and it also improves the flavor. Let the ice cream maker run for five minutes before putting the mixture in, so it freezes as fast as possible. Freeze a glass container to store the ice cream. And work quickly when the ice cream has finished churning. Allow it to harden overnight.


FOOD SAFETY

Ice cream is made from dairy products and eggs, so it is very important to take steps to ensure food safety. Follow the instructions in the recipe carefully.

  • Start with everything washed in hot soap water, including knives and cutting boards.
  • Use pasteurized cream.
  • Simmer the cream and fruit mixture for two minutes to bring it to a safe temperature.
  • Add the hot cream mixture to the egg mixture, which will bring the eggs up to 160 degrees F., the safe temperature for eggs.
  • Fresh fruit can not be added after this, because it is not cooked and could contaminate the ice cream.
  • Some recipes call for adding things after the ice cream is churned, such as nuts, preserves or chocolate. These should all be fresh, clean, and handled in a manner to keep them clean. Nuts should be toasted and cooled just prior to adding. Anything chopped should be done on a clean cutting board with a clean knife. Preserves should be a newly opened jar.
  • The ice cream should be consumed within a week.