• Question: Why does milk go off quickly?

    Asked by syra kate to Chris, Hayley, Jimi, Omur on 16 Mar 2016.
    • Photo: Jimi Wills

      Jimi Wills answered on 16 Mar 2016:

      Milk has lots of protein and sugar and fat that bugs can eat. Milk already has some bugs in , and every time you take the lid off more bugs get in. They grow and divide, feeding on the sugar and protein and fat in the milk. The warmer the milk is the faster they grow. That’s why we keep it in the fridge.

      The bugs mostly eat the sugar, called lactose, and they release lactic acid, which make the milk more acidic (sour) and causes the milk proteins to clump. That’s how yoghurt is made, and is also the first step in making cheese.

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