How to make ice cream in a bag

the science of ice cream left brain craft brainSunday, July 20, 2014 is National Ice Cream Day.  So of course we had to celebrate!  We did this by trying out the Ice Cream in a Bag technique over at a friend’s house today.  Plus we learned about the science of ice cream too!

Ice Cream in a Bag Recipe

We used the VERY! yummy recipe over at Spoonful for our ice cream.  Three simple ingredients: half and half, sugar and vanilla extract, shake inside a Ziploc surrounded by a another Ziploc full of ice and salt.  And voila!  Purely yummy soft frozen ice cream, ready to top with whatever toppings you like.

ice cream in a bag instructions left brain craft brain

The Science of Ice Cream

ice cream cup left brain craft brainWhat makes ice cream creamy?  This ice cream is made of sugar, fat, ice crystals and air.  The more you shake, the smaller the ice crystals become and the more air is incorporated into the ice cream.  Doing both makes for a creamier cream.  You can also adjust the creaminess by changing the fat content of your dairy – heavy whipping cream has 6g of fat per Tbsp. vs 3.25g for whole milk.  We went with half and half at 1.7g fat per Tbsp.

Why does shaking some dairy in a bag make ice cream?  Ice cream is an emulsion, which means small droplets of one liquid dispersed or spread throughout another liquid.  Think salad dressing…  Oil and vinegar don’t dissolve, but they can disperse into an emulsion with the help of a whisk.  So when you shake the bag, it emulsifies the ice cream, dispersing the ice crystals, fat molecules and air.

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Why do you need salt in the ice?  Salt lowers the melting temperature of ice.  This lets you shake that bag of ice long enough to get the ice cream to solidify.  The more salt you add, the lower the melting temperature.  And the colder the temperature of the icy solution around the ice cream, the faster the cream freezes. This is the same reason that salt is put on the roads when it’s cold and wet.  Lowering the freezing temperature (which is the same as the melting temperature!) keeps the roads covered with water, not ice.

ice cream collage 2Enjoy your ice cream!  And science :)  Did you like this?  Come like me on Facebook :)

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