Teach Every Day

Looking for a fun Christmas science activity to do for the holidays? Give your students a fun, hands-on experience in protein denaturation with this easy milk plastic activity. By adding heat and acid, students turn whole milk into biodegradable milk plastic! I love doing this experiment around the Christmas season, using the milk plastic to create unique ornaments for our classroom Christmas tree!

Before doing this activity, your students will need to have a basic understanding of proteins. Check out this resource! It is one of my favorite hands-on activities that really gives kids a solid understanding of how proteins fold, and denature! 

Materials for the Milk Plastic Activity

To begin, gather your materials: 1 cup of whole milk, 4 tablespoons of white vinegar, and a few common science tools like a glass beaker, hot plate. You will also need a strainer or cheesecloth. To make something fun with your milk plastic, provide food coloring, glitter (if you are brave!) and small cookie cutters. 

Whole milk makes the best texture, but 2 percent will also work well. One cup of milk yields about 1/3 cup of milk plastic. I allow my students to work in pairs. At the end they divide the milk plastic into two balls so that each can choose their own color and shape. 

Heating Up the Milk

The first step is to heat the milk gently until it reaches around 50-60°C (120-140°F). Stir occasionally to ensure an even temperature. The milk should be hot, but not boiling.

Students can use individual hot plates to heat the milk. You could also opt to heat all of the milk up at one time in a single pot or beaker. I have also had success using a microwave to heat the milk. 

Once it reaches temperature, take the milk off the heat and add the vinegar while gently swirling. The heat and acid cause the casein proteins in the milk to unwind, denature, and come out of solution. Curds will form as the denatured proteins separate from the whey. 

You made curds and whey! Just like Little Miss Muffet. 

Get this Christmas science activity for free! The free resource includes student instructions, a student lab sheet with questions, a key, and a full teaching guide. 

Straining Off the Whey

Pour the curdled milk into a piece of cheese cloth to separate the curds. Cheese cloth is very inexpensive and can be found at Walmart. In a pinch, paper towels will also work, but can be a bit more messy. 

Students can knead food coloring (and glitter!) into the curds and mold it into whatever shape they want!

Place shapes onto wax paper or a styrofoam plate to dry for 48 hours (or longer depending on the size). The milk plastic will become very hard and somewhat brittle once dry. 

Christmas Science Activity

Since I like to do this near Christmas time, so I encourage students to create ornaments, stars, snowmen, trees, bells. I provide a few small cookie cutters, but they are not necessary.  

If students are making simple colored balls, have them mold the balls around the end of a loop of yarn. Once dry, the loop can be used to hang the ball. If students make holiday shapes, use a pencil point to poke a hole through the shape before it dries. Then use a length of fishing line to tie loops through the hole for hanging. 

Biodegradable Milk Plastic

Milk plastic does not look or feel like the petroleum based plastics your students are familiar with. But it is ‘plastic’ because it is composed of long polymers – the denatured casein proteins, long stands of amino acids! 

This project gives you a chance to discuss sustainability and the issues with typical plastic waste. What kinds of applications are there for biodegradable plastics like milk plastic? What are the limitations? 

After a few weeks in the classroom (after Christmas break) I allow students to take home their creations, or donate them to science! We place the donated milk plastic ornaments outside in various conditions to observe how biodegradable they really are. 

Some are laid out fully in the elements, some are buried to simulate the situation at a landfill, some are kept under shelter outside. We then take weekly observations of the plastics to see how long they take to break down. The timing depends a lot on the weather (amount of moisture and heat)  and the size/thickness of the milk plastic creation! 

Research the Problems of Plastic

Use this activity as a jumping point for research. What is plastic doing in and to our environment? Look into the great Pacific Garbage Patch. Research microplastics (they are everywhere! Antarctica, in the air, in our bodies!). What types of solutions are being put forward for the problems of plastics? 

Biomolecules Resources

Want to do the milk plastic activity in your classroom? Download this free Christmas science activity resource from Science of Curiosity! It includes lab instructions, a student question sheet, key, and a teaching guide.

Science of Curiosity has a ton of fun, hands on and engaging resources to help you teach the biomolecules! My favorites are the doodle notes and the awesome no-prep biomolecules review game!

Happy teaching!