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How to Make Ice Cream in Freezer Bags

Whether it's National Ice Cream Day, or just any old day (because every day should be Ice Cream Day)—let's celebrate! Enjoy this family-favorite frozen treat by making your own ice cream at home in freezer bags. On a snowy day, you can use the same technique to use snow to make ice cream! Find out how at the bottom of this post.

Please note: While clean snow is used to make Snow Day Ice Cream, we do not recommend eating the snow itself. 

So you want to make some ice cream. That’s easy. Just follow the instructions in the graphic above and BAM! Ice cream. A sweet treat, neat and ready to eat.

But why? What makes those ingredients mix together in such a heavenly dessert? Why did you mix a bunch of salt in with your ice? I mean, the graphic kind of told you why, but what’s really going on here? In short, what is the science of why ice cream do how ice cream do?

Let’s start with the ingredients

The big four are:

  • Ice crystals
  • Fat
  • Sweeteners
  • Believe it or not, air

The ice crystals come from the water that’s in your milk, cream, and vanilla extract. You want small crystals because they’ll make the ice cream smoother. Think about it: the bigger the crystals are, the more likely you’ll be able to notice them when you’re eating. Fat and sweeteners are both primarily for flavor. Ice cream is 10% fat (from the dairy) minimum; anything lower and it has to be labeled as low-fat or something similar. The sweeteners (just plain sugar in this recipe) make the ice cream nice and sweet, of course, but they also lower the freezing point of the ice cream mixture (more on this later), which makes it less likely to freeze into a solid brick.

The air is kind of weird, but all ice cream is whipped to have some air content in the mixture. You can probably think of times when you’ve had ice cream and thought that it seemed exceptionally light, or exceptionally thick and heavy. That is all down to the amount of air. Ice cream manufacturers call the amount of air “over-run,” and typically the fancier your ice cream is, the less air they whip into it. That increases its density and thickness. Cheaper ice creams whip a bunch of air in there, which means you’re getting less actual ice cream in the same size container than the fancy stuff.

There is a fifth category of ingredients in ice cream, a category that I’m simply going to call “Other Stuff,” because that’s what it is. Other Stuff can be anything from chocolate chips or fruit pieces to proteins, flavors (like your vanilla base or cocoa powder), and special chemicals called emulsifiers. Here’s some fancy science: ice cream is a type of mixture called an emulsion, which is a mixture where the ingredients (in this case the fat and the water) don’t normally like to play nicely together. Emulsifiers help keep the fat and water from separating out and ruining the consistency and flavor of the ice cream.

Now let’s talk about that salt and ice mixture

Also, everything next also applies to the effect the sweeteners have on the ice in the ice cream itself.

In order to properly freeze your ice cream, you need something colder than freezing point of water to crystallize the ice in the cream. Regular ice won’t work, because it is exactly the freezing point of water. So if you don’t have an ice cream maker handy, you add salt to your ice. When salt hits ice (technically, when it hits the thin layer of liquid water on the outside of most ice you’ll deal with), it dissolves into two parts called ions. The ions float around in the water and get in the way of the water molecules, which is a problem when those molecules try to hook up and form solid ice. Which means that salt added to ice actually allows it to get colder than normal ice because it lowers its freezing point. This, incidentally, is why ocean water stays liquid even in very cold temperatures.

So you have your ice cream mixture that, thanks to the sugar, has a slightly lower freezing point than plain water, and you have your ice/salt which has a much lower freezing point than plain water, and you stick the cream in the ice, massage it to break up the ice crystals and spread out the fat particles and mix in some air, and all the while the salty ice is sucking heat from the mixture, cooling it down and thickening it into one of the most delicious of summer treats. And that, folks, is how ice cream do.

Turn your Snow Day into Ice Cream Day

With just a few tweaks, you can turn your Snow Day into an Ice Cream Day! Use clean snow to freeze your ice cream. We do not recommend eating the snow itself.

Here's what you do:


  • 1 Cup half and half or ½ Cup milk and ½ Cup cream
  • 2 Tablespoons sugar
  • ½ tsp of vanilla extract (optional)
  • 1 Quart sized zip top bag
  • 1 Gallon sized zip top bag
  • Salt—kosher salt or rock salt works the best
  • Snow—a lot of snow!
  • Gloves or oven mitts

How to make Snow Day Ice Cream

  1. Gather enough snow to fill a gallon sized zip-top bag, and be ready to gather more!
  2. Mix the half and half, sugar and vanilla extract in the quart sized bag.   Seal the bag tightly, removing as much air from the bag as possible.
  3. Fill the gallon sized bag half full with snow, and add 1-2 tablespoons of salt.  Place the bag of ice cream mix inside the gallon sized bag.  
  4. Fill the gallon sized bag with snow, adding 1-2 more tablespoons of salt.
  5. Wearing gloves or oven mitts, shake the bag or roll it on the table. As the snow compacts in the bag, add more snow and ice.
  6. Continue to stake or roll the bag until the ice cream mix is the consistency of soft serve ice cream. This might take 30 minutes. The key is to keep the bag moving, and add more snow as it compacts together.
  7. If the bag of snow turns into a slushy mixture, it’s okay! Thanks to the salt mixed with the snow, the slush is still cold enough to freeze the ice cream mixture.
  8. Carefully remove the ice cream bag from the larger bag, open it and spoon it into a bowl.  Add your favorite toppings and enjoy. 

Tips and Hints!

  • It’s important to keep adding snow, when it compacts inside the bag. This is because there is air trapped between the snowflakes, which makes it appear fluffy when it falls to the ground. As snowflakes are compacted together when making the ice cream, adding more snow to the bag will help the ice cream freeze.
  • Don’t forget the salt! When making ice cream, in a bag or in an old fashion ice cream maker, salt is a key ingredient that helps the ice cream freeze. The salt lowers the temperature where water freeze. Another way to think about this is that ice will melt at temperatures below 32 degrees Fahrenheit. This means when the snow starts to melt in the bag, when mixed with salt, it’s colder than 32 degrees.  For the ice cream mix to free, it needs to reach temperatures below 32 degrees.