Casein is the main protein in cows milk. It precipitates rapidly when vinegar is added to warm milk. The precipitated casein and other milk solids can be filtered, shaped and dried into a hard plastic like material frequently referred to as milk plastic.
Both full cream milk and low fat milk contain casein and give a good yield of product. The casein obtained from full cream milk gives a more pliable, less crumbly material, presumably due to the higher fat content. However, the solid also exudes more oily liquid during the drying stage.
We used the following recipe:
1. Heat 300ml milk to 65 C.
2. Add 20ml of white vinegar and stir.
3. Allow the precipitated casein to cool a little before filtering through a sieve.
4. Press the filtered solid between several layers of paper towel.
5. Mould the solid into the desired shape and dry in a low temperature oven or on a warm shelf near to a radiator.
Making milk plastic
Add vinegar and stir to precipitate out the casein and other milk solids.
A closer look:
Cottage cheese anyone?
Filter it through a sieve
Press out the excess fluid before drying
What shape will you make?
You can add food dye to colour the milk during the heating stage
The drying stage takes several days or even weeks, until a very hard plastic-like material is produced.
Hey presto! Milk plastic.
It’s too hard to eat, but it may still go mouldy under the right conditions.
Finally, on the chemical reaction in the baking powder submarine last time
The baking powder used in the toy submarine last time contained two active ingredients, disodium diphosphate and sodium bicarbonate. These two chemicals react to produce carbon dioxide which was released as bubbles that caused the submarine to rise.
Na2H2P2O7 + 2NaHCO3 → Na4P2O7 + 2H2O + 2CO2
This reaction tends to release carbon dioxide at a slower rate than the sodium bicarbonate reacting with an acid like vinegar.