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Denaturing protein


    Curdle milk in this experiment to see protein molecules form.

    Ingredients and equipment that you will need

    Any acid – vinegar or lemon juice work well

    Method and further information

    Pour a little milk into a glass – up to a height of around two centimetres. Swirl it around in the glass and look at it. It is liquid, with no lumps or bits.

    Now add a spoonful of vinegar or lemon juice and swirl again. This time you will see lumps of protein round the side of the glass.

    The protein molecules in milk fold up in a ball. Adding acid unfolds the molecules and then they tangle together. This is called denaturing or curdling. This is the first process in digesting protein and one reason why you have acid in your stomach.

    Be careful – you should ask an adult to help you with these experiments. Do your experiments in old yoghurt pots, jam jars or bottle tops. Don’t use cups or glasses in case someone thinks it’s a drink.