How to make casein from milk

Written by sarah davis
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How to make casein from milk
Turn milk into a firm, white casein paste. (amisb/iStock/Getty Images)

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.

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Things you need

  • 500 ml (2 cups) milk
  • 30 ml (2 tbsp) vinegar
  • Medium-sized pan
  • Cooking spoon
  • Fine-sieve strainer or colander
  • Cheese cloth
  • Small bowl
  • 5 ml (1 tsp) baking soda
  • Waxed paper
  • Aluminium foil
  • Rolling pin

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  1. 1

    If you are planning to make a plastic figurine, cover the mould or surface in aluminium foil smoothing out all wrinkles as you cover.

  2. 2

    Line the colander or strainer with a double layer of cheese cloth.

  3. 3

    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.

  4. 4

    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.

  5. 5

    When the milk begins to simmer turn off the heat and add the vinegar while stirring. The mixture will thicken and become slightly lumpy.

  6. 6

    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.

  7. 7

    Form the solids remaining in the cheese cloth into a small disc or ball and place it on the waxed paper.

  8. 8

    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.

  9. 9

    Wrap any unused casein tightly in cling film for up to four days before use. If air reaches the wrapped casein, it will solidify.

Tips and warnings

  • 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.

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