Kitchen Pantry Scientist: Tie-dye milk, Spy Juice

8:24 AM, Nov 18, 2010   |    comments
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GOLDEN VALLEY, Minn. -- The Kitchen Pantry Scientist Liz Heinecke joined us on KARE 11 News Sunrise again to show us the fun behind science.

Spy Juice

Using cranberries and baking soda, you can create invisible messages that will be revealed to friendly eyes and self-destruct before your enemies have a chance to read them.

You will need:

Half a bag of cranberries, water, baking soda, printer paper and a small paintbrush, Q-tip, or something else with an absorbent tip to write your message with.
Boil the cranberries in about three cups of water for 15 or 20 minutes. ( Be sure to put a lid on the pan.) Crush the cooked berries and push the liquid through a sieve or colander to collect the concentrated cranberry juice.

Let the juice cool and pour it into a large rectangular casserole dish or cake pan. If your cranberry juice seems thick and syrupy, add some water (maybe half a cup) so that it will soak into the paper.

Add 2 teaspoons of baking soda to about 1/3 cup of warm water and dissolve it as well as you can. (Don't worry if you can still see some baking soda.) Using a Q-tip, paintbrush, or your homemade writing tool, use the baking soda solution to write a message on your paper. Let your message air dry, or speed things up with a blow dryer. To reveal your message, place your paper in the cranberry juice and see what happens!

The science behind the fun:

Cranberries contain pigments called anthocyanins (an-tho-SY-a-nins), which give them their bright color. In nature, these pigments attract birds and other animals to fruit. This is important because animals eat the berries and spread plants seeds from one place to another.

These pigments, called flavanoids, change color when they come in contact with acids and bases. Cranberry juice is very acidic, and the pigment is red in acids. When you add it to a base, it turns purple or blue. Baking soda is a base, so your baking soda message will turn blue when it comes into contact with the pigments in the cranberry juice. Eventually, when enough cranberry juice soaks into the paper, it will dilute the baking soda and make the paper acidic, turning the pigment back to red and your message will disappear.

There are over 300 kinds of anthocyanins which are found in many fruits and vegetables including blueberries, red cabbage, grapes and blueberries. Scientists think they may have many health benefits and some researchers are even making organic solar cells using flavanoids. What other juices can you use to reveal secret messages? What other bases could you use as ink? Try making your own recipe for spy juice.

Tie-dye Milk

Food coloring isn't just for frosting any more! You'll be amazed as you watch the forces of surface tension at work in this "brilliant" experiment.

You'll need a small, shallow dish or plate, milk, dishwashing liquid, Q-tips and food coloring. Add enough milk to cover the bottom of the dish. In a separate small container, mix together about a half cup of water with a squirt of dish-soap (a teaspoon or so.) Put several drops of different colored food coloring into the milk (maybe two drops of each color.) Finally, dip a Q-tip into the dish-soap mixture and then touch the Q-tip to the milk. The detergent will break the surface tension of the milk and the food coloring will swirl around in interesting patterns, as if by magic.

Play with it! It works better if you don't stir, but you can keep re-wetting your Q-tip with soapy water and touching it to the milk.
Compare how the experiment works with skim milk versus whole milk.

What Happened?

Imagine that surface of liquids is a stretched elastic skin, like the surface of a balloon full of air. The scientific name for the way the "skin" of a liquid holds together is surface tension. When the skin of the liquid is broken, whatever is underneath will be able to escape, like the air rushing out of a balloon.

In this experiment, the surface of milk is like the elastic skin and dish detergent is what breaks the "skin" of the milk, sort of like a pin popping a balloon. Food coloring and more milk then escape from underneath the milk's surface, swirling to the top.

For more great science projects head go to:

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