This Magic Milk Experiment is a fantastic science investigation that is always lots of fun. With just a few simple ingredients you can learn all about soap and how it affects different kinds of milk.
You can do this experiment with young children, like preschoolers, to get them excited about learning. Or older kids can make their own magic milk science fair project.
Disclosure: Adult supervision is required for all activities at all times.
More STEM Activities to try
Kids of all ages love a classic science activity. If you want another fun way to teach your kids STEM, then check out these other fun activities.
- Make a Book – STEM Invitation to Play
- How to Make A Pom Pom Shooter
- Floating City – STEM activity for Kids
- What Melts In The Sun Science Experiment
- Pine Cone Science Experiment
For more ideas, take a look at these 42 STEM Activities for Kids.
Materials Needed
- 1 Cup of whole milk
- Food coloring
- Dish soap
- A plate
- Cotton bud (optional)
How to do the Magic Milk Experiment
1. Pour a glass of milk onto a plate.
You’ll need a wide, shallow dish for this simple science experiment. A plate, which allows for a thin layer of milk is perfect for watching the color explosion that is about to happen.
2. Add drops of food coloring.
I added a variety of colors to my milk. Just placing drops all throughout the surface of the milk.
You can add your drops wherever you like. If you are doing this with a curious preschooler who will want to try it more than once, you can even experiment to see what happens when you only place dots near the center of the plate versus what happens when you only place them around the edge.
I definitely added too much food coloring to my milk, feel free to just add a few drops because the experiment will still work.
3. Place a drop of dish soap in the middle
Place a little dish soap (you’ll only need a drop) in the middle of the plate.
I just poured mine straight out of the bottle. However, it may be easier for young kids to scoop up a few drops of soap using a cotton swab and then placing the swab in the middle of the milk.
4. Watch the reaction.
The colors in the milk will instantly move to the outer edges of the plate. But if you keep watching then you’ll see the constant movement of colour as the colors swirl around all by themselves. This is best to see in the video, which shows a sped up version of 10 minutes of the reaction happening.
The Science Behind the Magic
What is actually happening to make this milk magic?
Milk consists of a variety of different molecules including proteins, nutrients, fats and water. In this experiment we are going to be focusing on the fat molecules (which are non-polar) and water molecules (which are polar).
These two molecules do not mix. When they are in milk, they are floating around separately.
Soap is both polar and nonpolar, which means it will be attracted to and bond with both fat and water. The hydrophobic part will bond with fat and the hydrophilic part will bond with the water. This means that soap acts like a bridge or a magnet between these two different types of molecules.
Since soap is like a magnet for both fat and water, this means that when you add soap into milk these different types of molecules are going to be attracted to the soap. This movement of molecules is what you see in the experiment. Initially the movement you observe is of the separate fat and water molecules being attracted to the soap molecules, and then the whole soap/fat/water molecule as a whole goes flying around the plate.
Without food coloring, we wouldn’t be able to see this movement. By adding in some color, we can see how the molecules in the milk move around, causing tiny little currents for the food coloring to follow.
When all of the fat has been bonded by the soap then the reaction will stop and your experiment is complete. This is why milk with higher fat content will react for longer than skim milk, because it has more fat available to be reacted with.
Why is this important?
Knowing how soap works explains why it’s important to wash our hands to prevent the spread of diseases.
Bacteria are organisms, some of which (not all) can cause diseases.
The cell membrane of the bacteria (which is kind of like the skin of the cell) is made up of fats (otherwise known as a phospholipid bilayer). When we rub soap over our hands it bonds to the fat in the bacterias cell membrane (just like it bonded to the fat in the milk experiment).
Then when we place our hands under running water, the other part of the soap bonds with the flowing water. Since the water is flowing, it takes the bacteria it has already bonded to with it down the drain.
Turning it into an Experiment
The easiest way to turn this chemical reaction into an actual experiment is to try milks with different ratios of fat. You can try the same experiment with different types of milk (or water) and then time how long it takes for the reaction to slow down or stop.
Different types of liquids to try include:
- Water (0% fat)
- Skim or low fat milk (0.5 – 1% fat)
- Whole / high fat milk (3.25% fat)
- Whipping cream (30% fat)
This is a wonderful way to teach children about the scientific method. You can explain the basic principles of this easy science experiment and then get them to write down a hypothesis before timing how long the food colouring spreads.
You can also download and print the following recording sheet to use at home or in your classroom. Just click the large blue button below to get your copy.
Are you going to try the Magic Milk Experiment with your kids?
Don’t forget to pin the idea for later.
