LAMORINDA WEEKLY | Science in the Kitchen ~ Magic with Milk


Jefferson and Jonathan Wake make color swirls Photos Jennifer Wake

One thing you can find in just about every kitchen refrigerator is milk. Even if you're out of milk there are usually other things in the kitchen made from milk, like butter, yogurt, cheese, and ice cream. Here are a couple of easy experiments you can do using milk and cream.

1. Gather these supplies for your first experiment:

Milk (lowfat works well)

Pie pan or cake pan

Food Coloring

Dishwashing detergent

(one drop)

Toothpick

2. Start your first experiment:

Pour enough milk in the pan to cover the bottom (maybe 1/4 inch deep)

Carefully add two drops of food coloring to the milk in four different places. Pretend the pan is a clock face and place the drops at 12:00, 3:00, 6:00 and 9:00. If you like you can put different colored drops in each of those four places. Dip the end of the toothpick into the dishwashing detergent, and touch that soapy end into the middle of the pan.

3. What happened in your first experiment?

Milk is an emulsion. That means that it is made up of two liquids that do not mix together. Tiny particles of mostly fat are floating in mostly water, and fat and water don't mix. The food coloring mixes easily with the water part of the milk but not the fat. The detergent breaks up the fat and the result is the colorful movement you see. Try the experiment again with a different type of milk, like nonfat milk or soymilk. Do you get the same results?

4. Gather these supplies for your second experiment:

Sweet Cream

Jar with a lid

5. Start your second experiment.

Pour some cream into the jar until it is about half full. Put the lid on (tightly!) and shake it well for about 15 minutes. Open the jar and pour off any extra liquid.

6. What happened in your second experiment?

The cream is like the milk, made of mostly fat and water. The fat is surrounded by little bags called membranes. Shaking the cream breaks apart the membranes and the tiny fat droplets start joining together. Pretty soon the droplets start surrounding the water part, along with air bubbles from the shaking. So where the cream was a fat-in-water mixture (emulsion), it is now a water-in-fat emulsion. The water you poured off was extra water trapped along with broken air bubbles. You just made butter! Try putting some on toast to taste your experiment!

Jonathan Winter has been a science teacher at Lafayette Elementary School in Lafayette since 2001. He lives in Moraga with his wife, children, numerous pets - and he experiments frequently in his kitchen.