Kids STEM ActivitiesDecember 12th 2018

Easy DIY Plastic


Easy step by step instructions to make plastic out of milk!

Kitchen chemistry is a great way to introduce scientific concepts to kids by using materials that are familiar. Mixing milk and vinegar with a bit of heat we cause a reaction that turns the liquid into a solid that can be moulded and turned into anything. Even if you are doing this experiment with a toddler they will grasp that the milk isn’t the same anymore and how or why that has happened

The science

So… we’re not really making plastic but another substance called casein, which is latin for ‘cheese’. Casein is created when the protein and fat in milk meets an acid – in this experiment it’s vinegar – and splits into curds (the blobs) and whey (the watery liquid). This is because the casein proteins in milk don’t mix with the acid and so it forms blobs

This activity was inspired by Bex the Biochemist and Chelsea the Chef in both professions they need to know about how molecules are made up and what they can do to separate them.  It might be done with another substance, temperature or time. In our experiment it is both the acid from the vinegar and the heat that helps us to separate the molecules and then have them reform as a different polymer.

Lets make plastic out of milk!

You will need:

  • 1c milk
  • 1.5 tbl white vinegar
  • 4-5 drops of food grade dye
  • Small sauce pan
  • Sieve
  • Large bowl
  • Paper towels
  • Spoon
  • Cookie cutters
how-to-make-casin-plastic-step 1

Step 1. Pour Milk into saucepan and add 4-5drops of food colour.  Slowly heat the milk until steam is rising – DO NOT boil.

Once you can see a small amount of foam appear around the edge of the milk remove from the heat

how-to-make-casin-plastic-step 2

Step 2. Add 1.5 tablespoons of vinegar to the warmed milk and stir gently.  The milk will separate and the coloured solid is casein

Step 3. Scoop out the casein and place in a sieve. Gently smush to remove some of the liquid.  Beware not to over strain as it will make the casein plastic too crumbly to use

how-to-make-casin-plastic-step 3

Step 4. Transfer to a paper towel and gently pat down using a spoon or your hand.  This is where you can be creative – smush it flat and use cookie cutters or you can knead and roll the casein plastic to form shapes

how-to-make-casin-plastic-step 4

Step 5. Leave your shapes to dry for 24-48 hours.  This gives the plastic time to completely dry out and be used as Christmas ornament, beads or anything you have made

As your shapes dry they will become darker in colour and smaller

Questions to ponder

  1. Will more vinegar make more casein?
  2. Will you get the same results with low-fat milk, soy milk?
  3. Do all types of vinegar work?
  4. Will other acids, such as lemon juice and orange juice work?

This kids STEM activity can be used to promote:

Language skills: asking questions and inquiry, discussing procedural elements of the task, counting the bones

Social skills: Sharing ideas, working with a partner to create the shapes, turn taking

Fine motor skills: manipulating materials and tools, using tools to create shapes/cut

Please don’t forget to share your creations on social media using the hashtag #inspiredbyokdolls

Printables are for home and educator/classroom use.

Terms of use: Please do not edit artwork, crop or cut any graphic/logo/website of original.