Casein has many uses -- from an edible thickener in cooking to a surfactant in the manufacture of paint, dye and paper. It can also be used in simple plastics to make buttons, bags and jewellery. Also known as rennet, casein is a protein derived from milk that can be bought in powdered or paste form. For home application, it's easiest to use in a paste form, which you can then add to food or as a sort of moulding clay to make a plastic figurine. In food, use casein as a substitute for emulsified fat or cream.
If you are planning to make a plastic figurine, cover the mould or surface in aluminium foil smoothing out all wrinkles as you cover.
Line the colander or strainer with a double layer of cheese cloth.
Fully mix together 15 ml (1 tbsp) of milk and 5 ml (1 tsp) of baking soda in the small bowl so that no lumps remain.
Add the remaining milk and baking soda slurry to the pot and warm it on a hob on medium to low heat, stirring occasionally to ensure that it does not burn on the bottom.
When the milk begins to simmer turn off the heat and add the vinegar while stirring. The mixture will thicken and become slightly lumpy.
Pour this mixture into the cheese cloth-lined strainer over the sink. When all liquid has strained through the cheese cloth, pull up the sides and gently press out excess liquid.
Form the solids remaining in the cheese cloth into a small disc or ball and place it on the waxed paper.
If making a plastic figurine, roll out the casein ball to fit your mould and allow it to cure for about three days or until solid. If using as a food thickener, pinch off a small amount and whisk into the item to be thickened.
Wrap any unused casein tightly in cling film for up to four days before use. If air reaches the wrapped casein, it will solidify.
You will know when the milk begins to simmer when you see foam forming on the top and small bubbles rising. Do not bring the milk to a full boil.
If you are using a mould to form the plastic, you can replace the aluminium foil with a thick coat of solid cooking shortening to avoid all wrinkles and lines that may be created by the foil.
If you're mixing the casein into a large amount of liquid as a food thickener, it will blend in easier if you blend it with a small amount of liquid first, then mix the thickened liquid with the bulk liquid.
To make casein powder for extended shelf-life, roll the casein out into a thin sheet and allow it to dry. Break off small pieces from the sheet and grind in a coffee grinder to a fine powder.
Do not leave the pot of milk unattended while the heat is on.