This Week's Experiment - #279 The Science of Ice Cream
On the way home from the airport, I stopped by the grocery to pick up some
ice cream, for scientific research; of course. Then I had to eat enough ice
cream to come up with an idea for the experiment. To try it, you will need:
milk
sugar
vanilla extract
sandwich sized plastic bags (the "zip to close" kind works best)
a large plastic bag
ice
salt
a small dish
From the list above, you may have guessed that we are going to make some ice
cream. We will investigate some of the science involved in making good ice
cream.
Start with the sandwich sized bag. Into it, put one cup of milk, one
tablespoon of sugar and 1/2 teaspoon of vanilla extract. Close the bag and
shake it a bit to mix the ingredients. Open the bag and pour a little of the
mixture into a small bowl. Reseal the bag.
Put the bowl of mixture into the freezer. We will let it sit undisturbed as
it freezes. Put the sealed bag with the rest of the mixture into a larger
plastic bag. Add enough ice to fill the larger bag about half full and then
sprinkle a handful of salt onto the ice. Seal the large bag. Shake the bag
for about 5 minutes. If your hands get cold, you can wrap the bag in a towel,
or you can get a friend and play "cold potato" by tossing it back and forth.
Of course, then you would have to share the ice cream. Keep going until you
can see that the ice cream mixture is frozen.
After it is well frozen, open the large bag and pour out the ice and
saltwater. Open the small bag and use a spoon to taste your results. Yum!
You now have some homemade ice cream. As you eat it, pay close attention to
its texture.
By this time, the mixture in the bowl should be frozen. Try to eat this with
the spoon. Not as easy is it? And the texture is much different.
What is the difference? The biggest difference is that the mixture in the
freezer sat still as it froze. When the mixture is undisturbed, the ice
crystals grow quite large, making the ice cream very hard and icy. By
constantly disturbing the ice crystals, you wind up with lots of small
crystals instead of a few larger ones. This makes the texture of the ice
cream much smoother and more pleasant.
The mixing also traps air bubbles in the mix, making it fluffy and lighter.
You can see how much air they mix with store bought ice cream by letting some
melt and then refreeze. You will find that it shrinks by almost 1/3 of its
size once the air bubbles come out.
If you are a dedicated scientist, you could also test to see whether adding
chocolate syrup to the mixture changes the way that it freezes. Of course,
you should also test it with fresh strawberries, diced peaches, blueberry
jam, .............
From Robert Krampf's Science Education Company
PO Box 60982
Jacksonville, FL 32236-0982
904-388-6381
krampf@aol.com
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