Activities & Days Out / 5 August, 2026 / Nanny Anita
I’m not going to lie; making casein plastic from milk and vinegar is a really cool experiment. That takes no time to prep and about 5-10 minutes to do. I’ve seen it before as a milk into plastic experiment, but that isn’t completely true.
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To make your own casein plastic will need:
- 1 cup of milk
- 4 tablespoons of vinegar
- Sieve
- Kitchen towel
- Saucepan
- Food colouring (optional)
First heat the milk; it needs to be warm rather than boiling.
Next add 4 tablespoons of vinegar and then stir it together. I asked YC what she thought would happen and she thought it would fizz like the reaction you get when you add vinegar to baking soda.
You should immediately see the milk start to curdle. This is how cheese is basically made (please don’t try this though, it will taste horrid); obviously they don’t use vinegar.
Pour the curdled milk into a sieve to get rid of the excess liquid.
Put the remaining curds on the kitchen towel, cover it with some sheets and press down to remove any remaining liquid.
You should be left with a malleable substance. YC decided that she wanted to turn them into cakes; she got a little chocolate mold and pushed it into them. You could also use a cookie cutter to make your shape. We added a little food colouring, but that is optional.
If you leave it for 48 hours you should be left with a hardened plastic like shape.
The Science Behind It
Until the mid 40s there were many items that where made out of this milk plastic, otherwise known as casein plastic. Obviously this plastic is very different from the plastic we use today which is made from petroleum.
Plastics are a group of materials that may look and feel different, but can all be molded into different shapes. All plastics are made of molecules that repeat themselves in a chain, this is called a polymer. These can either be made of one type of molecule or different ones, which are linked together in a pattern.
Milk has many molecules of a protein called casein. When the milk is heated and an acid is added, like vinegar, the casein molecules unfold and reorganise into a long chain. This is a polymer, which can be scooped up and molded.
Pretty cool huh!
Edible Version
As I said earlier this is basically how cheese is made, with a few steps left out. If you wanted to try the experiment again and use lemon juice rather than vinegar, you would get Paneer which is a cheese commonly found in South Asia. YC was really excited to try it again with the lemon; she even tried it, but wasn’t overly impressed with it.
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