Follow the simple step-by-step below and then grab 30 more easy-to-follow science experiments kids will beg to repeat (plus a no prep science journal to keep track of their results!) in our shop!
To make rainbow milk, you can choose to keep it super simple and use only one kind of milk, or you can really get those scientific wheels turning and compare what happens with various kinds of milk. Whatever you choose, the set up only takes a few minutes.
To prep, I gathered a few supplies:
- A pint of 2% or whole milk
- A pint of fat free and heavy cream (if you choose to compare milks)
- A shallow pan or plate for each type of milk
- Non-gel food coloring
- A measuring cup
- Dish soap
Making Rainbow Milk
As soon as I walked outside with the armful of supplies, my 4 year-old came running over. I lined up the three pie pans and placed a carton of milk in front of each pan. Then, I asked her to measure two cups of fat free milk for the first pan. She carefully measured, poured and then repeated with the whole milk and heavy cream.
Starting with the center pan of whole milk, I placed two drops of each color (red, yellow, green, blue) in the center of the pan. I handed her a clean Q-tip and asked her, “What do you predict will happen if you place the Q-tip in the center of the milk but don’t mix it?”
“It will all mix together,” she quickly replied.
“Let’s see if your prediction is right,” I said as I helped her insert the Q-tip into the milk without mixing.
“It didn’t do anything,” A said with disappointment.
Next, I added a drop of dish soap to a new Q-tip and asked A what she thought would happen if she placed the Q-tip with soap into the milk. “Nothing,” she answered. A was fascinated when she carefully put the Q-tip into the milk and the colors instantly swirled around. Rainbow milk! She kept placing the Q-tip in and out of the milk to watch the colors race into a swirly rainbow.
“What do you think happened to the rainbow milk?” I asked A.
“The soap made the colors move,” A answered. I explained how milk is made up of many things including water and fats and that fats act like oil. We have done experiments with oil and water before so she knows water and oil don’t like each other. I then explained how one side of soap like oil/fat and one side likes water, so when the soap was added to the milk, the soap molecules moved through the milk, looking for fat.
“The soap moving through the milk made the colors move,” I said to A. “Now if we did this with milk that had no fat, what do you predict will happen?” I asked.
“I don’t know,” she replied.
“If there is no fat to search for, do you think the soap will move?” I asked.
“No,” A said. So, we repeated adding the dye to the fat free milk to attempt rainbow milk again. This time when I handed her the clean Q-tip I asked her why we are trying it with a clean Q-tip. I explained we had to see if a plain Q-tip would cause a reaction. Since we know it didn’t do anything, we know that it was the soap that was causing the colors to move. “The plain Q-tip is what scientists call the control, ” I told A. We repeated the experiment with a soapy Q-tip and was surprised when the dye actually moved.
“Hey, it moved!” A exclaimed. Turns out fat free milk isn’t truly fat free.
“Does that one have fat in it?” she asked pointing to the heavy cream. “Yes, it has a lot of fat,” I replied. We predicted the dye would move a lot. Again, we were surprised when the dye didn’t move at all. “What do you think happened?” I asked. “Did you notice something about the cream when you poured it?” I questioned.
“It was thick,” A said as she stuck her finger in. “Do you think the thickness made it hard for the soap to move?” She leaned over the pan to look closer and noticed the soap was still sitting in a little drop in the cream.
“The soap is right there, it didn’t move at all,” she said. Then, she quickly moved back to the first pan to dip her Q-tip back in.
We ended up pouring out the pans and repeating the experiment with the whole milk for A and her little brother to make the magic rainbows swirl. This experiment was a hit and a easy way to introduce some science terms like prediction, control, reaction, and result. We’ll be repeating it again and again as it was simply magical!
Get 30 More Science Experiments!
Grab 30 easy-to-follow science experiments kids will beg to repeat (plus a no prep science journal to keep track of their results!) in our shop!