Cooking Up Science: Ice Cream, You Scream!

As hot weather creeps towards Oregon, the thoughts of many turn to usual summer pastimes: swimming, hiking, barbeques, and of course, ice cream! Beyond the love affair with our taste buds, there’s a lot of cool science behind this sweet treat. Keep reading to learn what makes ice cream so sweet and smooth, and how you can make it at home without any fancy equipment!


By weight, the main ingredient in ice cream is water. This water mostly comes from milk, the main ingredient in most ice creams. Milk is about 87% water and 4% milk fat. Fat is a lot like oil, and if you’ve ever tried to mix oil and water together you know what happens.(If not, try it now!) Fortunately, cows are amazing water and fat mixing machines. Their bodies emulsify the fat and water. That means the fat is so finely dispersed throughout the water that it can’t clump up and float to the top.
Additional fat in the form of cream is another key ingredient in ice cream, and serves four main purposes:
1) it keeps your ice cream just soft enough to get a spoon into it;
2) it insulates the tiny ice crystals to keep them from melting quickly;
3) it mixes with air and creates fat foam that give ice cream a sturdy structure; and
4) it just tastes good!
Despite this tastiness, fat has so many calories that some treats (dairy and non-dairy alike) have stabilizers in place of milk fat. These ingredients—with names like xanthan gum, carrageen, sodium alginate, and eggs—do the same job as fat without contributing as much to your waistline.

As ice cream freezes it needs to be stirred frequently. This helps to mix in the air that forms the fat foam and also breaks up any large ice crystals that may grow. When things freeze quickly, the molecules don’t have a lot of time to arrange themselves into a few large crystals so instead form many small ones. The many small ice crystals in ice cream make it smooth and creamy. A slow-freezing ice cream would have large crystals that would give the ice cream a crunchy, cereal-like texture.

Even though your ice cream may feel frozen solid, up to a third of the water stays liquid, all thanks to sugar. Sugar dissolves very well in water but interferes with the water molecules’ ability to get near each other and lock into the solid ice crystal structure. At temperatures below freezing, these molecules stay in their liquid state in tiny sugar-filled pockets throughout your ice cream. This lends to ice cream’s scoopability and your ability to taste the sweetness through the chill.

After all this information, I can imagine that you are starting to get a hankering for this cool sweet treat. Don’t worry, OMSI has you covered! You won’t need any fancy equipment for our recipes below, just two plastic bags, some ice, and some salt. The salt lowers the freezing temperature of the ice, and the colder temperature freezes the ice cream faster. Enjoy! Dairy Ice Cream Ingredients:
2 c. whole milk
1 c. whipping cream
1/3 c. sugar
1 tsp. vanilla extract
other flavoring ingredients (optional, see suggestions below)

OR

Non-Dairy Ice Cream Ingredients:
2 c. soy milk, almond milk, or coconut milk
1/2 c. canned coconut milk
1/2 c. sugar
1 tsp. vanilla, almond, or coconut extract
Other flavoring ingredients (optional, see suggestions below)

Supplies:
Ice salt
2 1-gallon zip-sealed plastic bags

Procedure:
1. Pour the milk, cream, sugar, and vanilla into one of the plastic bags and seal it well. Shake the bag gently to mix all of the ingredients together.
2. Fill the second bag about halfway with ice and sprinkle very generously with salt.
3. Place the first bag (still sealed) inside the second and seal the second bag. Do not let the salt and ice get into the ice cream mixture! Shake these continuously for 20 minutes or until the ice cream mixture in the inner bag is frozen.
4. Eat and enjoy!

Optional: 
Change the flavor of your ice cream by adding other ingredients to the bag in step 1! 
- Try a different extract flavor, like orange or raspberry 
- Crush your favorite candy bar 
- Mash up about 3/4 c. of your favorite fruit 
- Add 1/2 c. chocolate chips, chopped nuts, or shredded coconut
- Use chocolate milk instead of regular milk, or add 1/3 c. chocolate syrup 
- After 10 minutes of shaking, add 3/4 c. miniature marshmallows 
- Use brown sugar instead of white sugar 
- Add a dash of salt—this is especially tasty with coconut milk



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