Goldsmiths’ 2013

Making Plastic from Milk!

Milk contains a protein called casein—from the Latin word “caseus” meaning cheese. Casein is a polypeptide which is relatively insoluble in water. Milk is white because of the tiny particles of casein suspended in the solution—not dissolved.

This experiment uses the casein present in milk to make a natural plastic.


100ml whole milk;

10ml white vinegar;

Saucepan or large glass beaker;




1. Measure out 100ml of milk. Heat the milk in the beaker whilst stirring until it is hot, but not boiling—this will not take long if you are using a Bunsen!


2. Remove the milk from the heat. Then whilst stirring, add 10ml white vinegar. The casein should precipitate out in clumps.

3. Separate the casein from the remaining solution using the strainer. Squeeze as much liquid out of the casein as possible—the more liquid removed the better!


You can now mould your plastic into any shape you like. Leave it to dry on a radiator or in the sun for 24 hours. The result should be a fairly strong piece of biodegradable plastic which you can decorate!


1. Will more vinegar result in more casein?

2. What happens with low-fat milk, or soy milk?

3. Do all types of vinegar work?

4. You may wish to try some different acids e.g. lemon juice.

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