Ice Cream and Air Experiment #433
Grade Level(s): 1-2, 3-5, 6-8
By: Robert Krampf

July is National Ice Cream month, so I thought I should do an experiment that focused on ice cream. I usually have to find a way to tie ice cream in, but this week ice cream is the main focus.

Materials:

a grocery store that sells ice cream and has a scale in the produce department.
a small container of ice cream

Plan:

First, go to the ice cream section of your grocery. Look around at all of the different brands of ice cream. Find the cheapest ice cream, and the most expensive. There will probably be quite a difference in price. Some of that price difference is due to expensive flavorings and the amount of butterfat, but it is also due to something that is all around you. Air.

Air? What does air have to do with ice cream? Air is added to give the ice cream a soft texture. The mixture needs a certain amount of air bubbles mixed in with it to make it pleasant to eat. Without that air, the ice cream would be more like eating chunks of flavored ice.

Some types of ice cream use more air than others. This air takes up room, which means that it takes less ice cream mixture to fill the container, which means it costs less. The space taken up by air is called the overrun. In the United States, up to half of a container of ice cream can be air.

Find similar sized containers of cheap and expensive ice cream. Try to use similar flavors, since added fruit and nuts can change the total weight. Lift one in each hand and you will probably be able to tell which is heavier just by lifting them. If not, take them to a scale and weigh each one. If they both contain the same volume of ice cream, the cheaper one will almost certainly weigh less, although some expensive ice creams have high overrun too, so try several brands.

You can also measure overrun by melting the ice cream. Buy a small container of ice cream and place it in the refrigerator instead of the freezer. Leave it overnight to melt. You will probably have to stir it a few times to break up the foam, so that all the air can escape. When all the air is out, it will look like a lot of the ice cream is missing. Actually, the container still has the same amount of stuff. Part of the container is taken up by liquid, and the rest by air. Now they are separate, instead of being mixed together.

So is over run bad? Should we start a campaign to keep air out of our ice cream? Wouldn't it be better to have "pure" ice cream without the air? To find out, put the melted ice cream into the freezer overnight. When it is frozen, try to scoop up a spoonful. Be careful not to break the spoon. If you can break off a piece, try eating it. That is why we melted the ice cream in the refrigerator instead of just sitting it on the table, where it might spoil.

Of course, you can also compare overrun by eating the ice cream. Ice cream with a low percentage of air will be denser and creamier. Ice cream with a lot of air will be light and fluffy. Less liquid and more air makes it melt faster, so be careful with the hot fudge sauce.

From Robert Krampf's Science Education Company

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