Visit | Milk Mystery

Lab at Home

Watch colors swirl mysteriously in milk!
milk poured

Materials

  • Whole milk
  • Small dish with a flat bottom (we use a Petri dish in the Lab, but you can use a small pie plate)
  • Ruler
  • Food coloring (4 different colors)
  • Wooden toothpicks
  • Liquid detergent
  • Optional: Skim milk, buttermilk, cream, half & half, water, oil, pepper, plastic toothpicks, hand soap

Procedure

  1. Fill the dish about 1/4 inch high with whole milk.
  2. Let the milk sit for a moment until there is no movement.
  3. Place one drop of each of the four food colorings in the milk in four different
    locations. WARNING: Food coloring can stain clothing and hands.
  4. Here is a diagram to follow:

  5. Put liquid detergent on the tip of your toothpick.
  6. Touch the toothpick to the milk at the center of the dish and hold the toothpick just off the bottom of the dish.
  7. What happens? Make some observations.

Extension

Write a hypothesis about why the colors started moving. Was it the fat or proteins in the milk? Was it the detergent? After you make a prediction, test it out by changing one variable in your procedure at a time. For example, if you think that the experiment works due to the interaction between soap and fat, repeat the experiment once using no soap on the toothpick. Then repeat the experiment a third time, but substitute whole milk with skim milk. Be sure to clean your dish well between experiments.

Here are some suggestions:

  • Substitute whole milk with skim milk, buttermilk, cream, half and half, water, or oil
  • Substitute a wooden toothpick with a plastic toothpick
  • Substitute the liquid detergent with hand soap or don't use soap at all
  • Substitute food coloring with pepper