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Why does milk turn sour?

After being in the fridge for one or two days milk turns sour. But you can make it sour and turn it into cottage cheese not in two days, but in two seconds.

To do this we must add some vinegar to the milk. Curd will immediately secede.

Cottage cheese is casein, milk protein. It is dissolved in milk, like sugar in water. But it is necessary to add some acid to milk to make casein separate.

But nobody add acid into milk. Why does it turn sour?

Tiny fungi like yeast, which fly in the air, are to blame. Once in the milk, they start their work and convert milk sugar to lactic acid. And then the acid makes milk sour.

To protect milk from souring you should boil it. Boiling kills fungi.

Sometimes milk clots during boiling. That's because fungi has already worked in it and made acid.

Why do the holes in cheese appear?

If you hold the cheese a little longer in the cellar, the fungi’s work will continue, and eventually your curd will turn into a cheese.

Holes in the cheese, as well as holes in the bread, are made by carbon dioxide.

From what do we get carbon dioxide?

It is produced by fungi.

Silverware can be polished by milk

After being processed by sour milk your faded silverware can look like the new one. If the milk is fresh, then it is necessary to add some vinegar (and get sour milk). Moisten silverware with sour milk, leave for half an hour and then wash with soapy water and polish with a soft cloth.

1 kilogram of cheese from 10 liters of milk

Milk is a source of calcium and vitamin D, so necessary for the construction of the skeleton and its strength; phosphorus and vitamin A, which are required for mental function and vision; magnesium, potassium, sodium, and B vitamins – essential for the functioning of the cardiovascular and nervous systems; vitamins C and E support the hormonal, immune and reproductive systems of the body.