Coagulation of Milk Proteins

Using common materials, demonstrate how milk colloids coagulate by adding an organic acid. In this demonstration, the ratio of milk, water, and acid is important. Your ratio may vary depending on your water's alkalinity, and the acid strength. Vinegar will give the most consistent results, but it's just a kick to squeeze a lemon at the demonstration for the younger students. For easier storage of metals use dry powdered milk. Just a suggestion, you may want to try this at home to make sure it works with your materials.


  • One beaker to hold 1 liter
  • One of the following acids: 25 mils white vinegar, 50 mils lemon juice, or the juice of one lemon
  • One stirring spoon
  • Measuring utensils
  • Milk (Either 120 mils 1% or 3 heaping teaspoons nonfat dry milk)
  • Water


Measure 900 mils water and add your choice of 1% or dry milk. Stir the mixture and add the acid while stirring. Let settle. Some floc may settle and some may float.

The water will stay cloudy, but most of the milk proteins will coagulate under acid conditions. If there is too much milk, the proteins will not separate. Too little or too much acid and the milk won't coagulate.

It's my understanding that the milk proteins don't like the acid conditions. When the acid is added they come together and form a larger mass, which has less surface area exposed to the acid environment.


School Talk Ideas, Demonstrations and Lessons