Casein is a protein that makes up approximately 80 percent of the total protein content of cow's milk. Existing as globules within the milk and largely responsible for giving milk its white color, casein precipitates out of solution when heated and then exposed to acid. A simple acetic acid solution, in the form of white distilled vinegar, works well to extract casein from reconstituted nonfat powdered milk. The precipitated casein forms an elastic white material that you can remove from the liquid within milk.
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Combine 50 g of powdered nonfat milk and 1 pint of distilled water in a heat-resistant glass container.
Heat the mixture to 105 degrees F. Monitor the temperature using an electronic thermometer.
Add the vinegar slowly to the milk mixture. Stir the mixture gently with the plastic spatula. Continue to add vinegar and stir the mixture until the casein begins to precipitate from the liquid in small blobs of white solid matter.
Press any precipitated casein to the side of the glass container with the plastic spatula, allowing the liquid to drain to the side of the container.
Collect the casein with the spatula and transfer it to another container. Continue to add vinegar and remove precipitated casein until no more casein forms.
Pour off any liquid that may have separated from the casein in the other plastic container.