what chemically happens to milk when it goes sour?

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what chemically happens to milk when it goes sour?

In: Chemistry

The lactose (milk sugar) is converted to lactic acid by lactobacillus bacteria (same ones that make yoghurt and cheese). The increased acidity causes the milk proteins to denature (unfold), exposing bits of protein that are hydrophobic (want to stay away from water). These bits then stick to each other, making clumps that hide the hydrophobic bits from the water.