How an Ice Cream Float Works

    An ice cream soda or ice cream float is made by adding soda pop or seltzer to ice cream. Some people add flavoring, like chocolate syrup, or a little milk. However you make it, as soon as the soda hits the ice cream you get fizzy, frothy, tasty bubbles.

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    Do you know how it works? It's basically the same as what is going on with the Mentos™ soda fountain (see “Mentos Mayhem” September 2004 ChemShorts), except not as messy. You are releasing the carbon dioxide in the soda out of solution. Bubbles of air in the ice cream provide nucleation sites around which carbon dioxide bubbles can form and grow. Some ingredients in the ice cream lower the surface tension of the soda so the gas bubbles can expand, while other ingredients trap the bubbles in much the same way as small amounts of protein in seawater trap air to form seafoam.

    Very popular varieties include black cows (cola and vanilla ice cream), brown cows (root beer and vanilla ice cream), and a coffee cola float (which is both bubbly and caffeinated). For kids, purple cows are also a big hit – they are both frothy and leave a purple tongue and mustache – a double win.

    A Purple Cow has purple grape juice and milk and/or milk products. Here's a few versions; take your choice.

    Purple Cow #1

    1 1/2 cups cold skim or reduced fat milk

    3 tbsp frozen grape juice concentrate

    1/2 cup low-fat vanilla frozen yogurt or ice milk

    5 medium ice cubes or the same amount of crushed ice

    Place all ingredients in a blender and process until smooth.

    Purple Cow #2

    3/4 cups 1 percent low-fat milk 

    1 1/2 tbsp frozen grape juice concentrate 

    1/4 cups fat-free vanilla yogurt 

    Combine ingredients in a container with lid and shake until well blended. Pour into a tall glass. 

    Welch's Purple Cow #3:

    in a 12 oz. glass combine two scoops of vanilla ice cream with chilled Welch's purple grape juice. 


    Kathleen Carrado Gregar, PhD, Argonne National Labs 
    [email protected]
    September 2008


    Reference:  Anne Marie Helmenstine at: and