The Science of Ice Cream (kitchen science)

[science_spot]

July is National Ice Cream Month!  Ice cream is one of my favorite things, and making it at home is also a great (easy) science activity for kids of all ages (see notes below).  There are a few great scientific concepts that can be learned easily through homemade ice cream.  And the best part is... it's edible!

 

For this activity, you will need the following materials:

1 quart size Ziploc bag

1 gallon size Ziploc bag

1/3 cup milk (vitamin D milk will work the best, but you can use a lower fat kind)

1/3 cup half & half or heavy cream (if you omit this ingredient, increase the milk about to 1/2 cup)

1/4 teaspoon vanilla (or a squirt of chocolate syrup)

2 tablespoons sugar

2 cups ice

1/2 cup salt (larger grain salt will work the best, but table salt is fine)

gloves or a small kitchen towel (to protect hands from the cold bag)

bowl & spoon

thermometer (optional)

 

Procedure

1.  Add milk, sugar and vanilla (or chocolate syrup) to the smaller bag.  Squeeze the sir out of it and zip it closed tightly. 

2.  Add ice to the larger bag. If using the thermometer, record the temperature of the ice.  Add the salt to the large bag.   Place the small bag in the large bag and zip the large bag closed.

3.  Wearing gloves, or using the small kitchen towel to protect your hands, rock, shake and jiggle that large bag until the contents of the smaller bag have solidified; this could take about 15 minutes.

4.  Open the larger bag.  If using the thermometer, record the temperature of the salty ice.  Remove the smaller bag and scoop the ice cream into a bowl.  Enjoy!!

 

The Science

For the youngest kids, ages 4-8:  Talk about what a liquid is (something that cannot hold its own shape, like milk), and what a solid is, like the sugar and ice.  At the end, show how the solid ice melted into liquid water and the liquid milk froze to solid ice cream!  You can even leave out some extra ice cream and show how it turns back to a liquid once it melts.

For all ages:  Most of you have probably guesed the milk, cream, vanilla and sugar are the ingredients that make up the ice cream once mixed together and frozen.  If you used milk only, your finished product is really ice milk, not ice cream.  This difference in name reflects the lower fat content of your milk and ice milk.  If you used the cream in your recipe, the fat content is higher and your finished product really is ice cream.

For older kids, ages 8-ish and up: The purpose of the salt and ice mxture is to freeze the ingredients in the small bag.  Using just ice would only be able to freeze water (about 32F), but the milk mixture freezes at a lower temperature.  Adding salt to the ice lowers its freezing temperature about -6F.  If you recorded the temperature of the ice and salty ice, you will see they are different.  This decrease in freezing temperature means the salty ice will take more heat energy from the milk mixture (and your hands) while it is thawing.  Removing heat from the milk mixture is what causes it to freeze.

For older kids, ages 8-ish and up:  You can experiment using different kinds of salt.  Table salt and kosher salt are both made of sodium chloride (see my past post on salt), but kosher salt has larger grains.  Using a salt with larger grains will dissolve in the melting ice slower, which will slow the freezing of the milk mixture, making for a smoother ice cream.  If you use rock salt (calcium chloride) instead, the different chemical will allow you to achieve a much colder ice mixture temperature: -20F!  Make sure you wear gloves!

 

Additional Concepts

For older kids, ages 8-ish and up:  Once you have discussed this activity with your kids, you can continue on to a discussion about melting ice on the roads during winter time.  Some states use different types of salt, based on the temperature range expected.  The concept of changing the freezing temperature of the ice is the same as in our ice cream activity above.

If you would like a complicated (and delicious) homemade ice cream recipe and discussion, check out sci-toys.com  .

You can add to this experiment by trying different types of salts.  I do NOT recommend the liquid nitrogen or CO2 fire extinguisher methods you may find on the internet.  These items can be dangerous in the kitchen, may render the ice cream inedible due to chemical contamination, and actually freeze the ice cream by a different method.

 

Enjoy your kitchen science!

 

Tonya

AKA sunmoonstars

The Science Spot

 

 

  

 

 

[comfycouch]

Jul. 6, 2009 at 1:21 PM

I love this recipe!  I did it with my kids for years when they were little and with my first graders when I taught first! Thanks for posting this.

[Mama0f3grlz]

Jul. 6, 2009 at 6:01 PM

So cool! I can't to try this one with my kiddos.

[TwinMomma122304]

Jul. 6, 2009 at 9:22 PM

Yay!  Something fun (and yummy!) I can do with my 4 year olds!  =)

[PaxMommy]

Jul. 7, 2009 at 3:08 PM

I'm going to do this with my kids! I'll let you know how it turns out:)

[arthistmom]

Jul. 7, 2009 at 4:50 PM

I told my husband about this kitchen experiment and he's excited to do it with our son, his partner in all things dessert. Thanks for the great idea! :-)

[Mickey28]

Jul. 9, 2009 at 2:10 PM

It's going to be quite a while til our little one to be is old enough to try this one, I'll have to make sure it works and test it in that time hahahaha... YUM!!