Turn kitchen ingredients into a science experiment! Learn how to make plastic from milk using simple chemistry. This fun and Earth-friendly science project is perfect for any time of the year. Kids will be amazed as warm milk and vinegar transform into a moldable plastic-like material.
Milk and Vinegar Experiment
Field of Science: Chemistry
Grade Level: 1st–6th Grade
Concepts Explored: Chemical reactions, polymers, acids and bases, casein protein
When you mix warm milk and vinegar, a chemical reaction causes the milk protein (casein) to separate and form curds. These curds can be molded into shapes and will harden over time—just like plastic! This activity explores the science of polymers and how they can form from everyday ingredients.
💡 Find all of our Chemistry Experiments for kids here. You can also learn how to make bioplastic ornaments here.
Materials:
- 1 cup milk
- 4 tablespoons white vinegar
- Sharpies
- Cookie cutters
- Strainer
- spoons
- Paper towels
How to Make Plastic Milk: Plastic Milk Demonstration
Watch the Video!
STEP 1: Add 1 cup of milk to a microwave-safe bowl and heat for 90 seconds.
STEP 2: Mix in 4 tablespoons of vinegar and stir for 60 seconds.
Stirring slowly, you’ll notice that solid chunks called curds start to form and separate from the liquid called whey.
STEP 3: Pour the mixture into a strainer and press out all the liquid leaving just the solid clumps or curds behind. This will resemble the consistency of ricotta cheese!
STEP 4: Press the paper towel into the strainer to soak up any of the leftover liquid or whey and remove it.
STEP 5: Lay out a piece of paper towel, place a cookie cutter onto the paper towel, and press your vinegar-milk mixture or plastic dough into the cookie cutter and let set for 48 hours.
STEP 6: Wait the 48 hours and color with a Sharpie if desired!
What Happens When You Mix Milk and Vinegar?
This milk and vinegar experiment does not produce real plastic. The new substance is called casein plastic. Plastics are a group of different materials that may look and feel different but can be easily molded into different shapes.
💡 If you want to explore real plastic polymers, try some homemade slime! Click here to read all about making homemade slime for easy science.
This plastic-like substance forms from a chemical reaction between the milk and vinegar mixture. When the molecules of a protein in the milk, called casein, comes in contact with the vinegar, the casein and vinegar do not mix. When the milk is heated, the casein molecules, each a monomer, unfold themselves, move around, join forces, and create a long chain of polymers, creating the casein plastic!
The casein molecules become these plastic-like blobs you can strain and mold into shapes. This is one way of making simple cheese from milk.
💡 Remember that the milk might smell strong while experimenting with it!
Make It a Science Project
Want to go further than just an activity? Turn this into an actual experiment! Try changing one variable at a time and ask questions like:
- What happens if you use low-fat or non-fat milk instead?
- Can lemon juice work instead of vinegar?
- How does changing the vinegar-to-milk ratio affect the result?
🔎 Use the scientific method, write a hypothesis, and choose variables! Look through our science fair resources here.
Plastic Milk Extension Activities
- Color the Plastic: Use food coloring in the milk before adding vinegar.
- Compare with cheese-making, research how cheese is made from curds and whey.
- Explore Other Polymers: Try slime, bouncy balls, or oobleck to see how polymers behave differently.
Free Chemistry Challenge Calendar
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More Helpful Science Resources
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- Best Science Practices (as it relates to the scientific method)
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- All About Scientists
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If you’re looking to grab all of the printable science projects in one convenient place, plus exclusive worksheets, our Science Project Pack is what you need!
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