Why does milk turn sour?

Question

Can you tell me why this happens by applying scientific methods.

Answer 1

Milk bacteria use lactose as an energy source, they change it into
lactic acid, which makes the milk taste sour. For what it's worth, lactic
acid is the same substance that accumulates in our muscles during intense
"aerobic" exercise and makes them feel like they're burning. To produce
lactic acid, the bacteria must first split lactose into its two component,
simple sugars, glucose and lactose. These can diffuse into to bacterial
cells and be used as energy sources. The principal protein of milk �
casein � turns into curd in this acid environment, so another way of
describing sour milk is to say it "curdled." Both the lactose and the
protein are used by the bacteria to produce additional bacterial cells.
Eventually, other kinds of bacteria (and even molds, if air is available)
may grow in the milk and make protein derivatives that smell really bad;
this is called "putrefaction."

Answer 2

What Makes Milk Sour

Answer 3

Milk, naturally, contains various bacteria that, although not harmful to humans, use the lactose (a sugar) found in milk in their respiratory functions. Lactic acid forms as a by-product of this and this lactic acid is what's responsible for milk turning sour. You can sort of test this yourself, if you're interested. If you go to a farm and ask for unpasteurized milk, and, at the same farm buy the same amount of pastuerized milk, then leave both in the fridge, you'll notice that the unpastuerized milk turns sour a lot faster. This is because pastuerization kills a lot of the bacteria that are responsible for the production of lactic acid. And although sour milk is a pain, if these bacteria didn't exist, we wouldn't really have cheese, cottage cheese, buttermilk, or sour cream, as they are also responsible, in some ways, for the production of all these products.

Answer 4

Milk is often naturally contaminated with bacteria called Lactobacillus. When the milk is prepared to be sent to the bottling company it is pasturized. This process helps to kill a large amount of this bacteria and make the milk suitable for storage and drinking. However, since this does not kill all the bacteria, those left will reproduce. Eventually the bacteria in the milk will produce enough of their waste products to sour the milk. The waste product is an acid which gives milk its soured smell and taste.

Answer 5

This Site Might Help You.

RE:
Why does milk turn sour?
Can you tell me why this happens by applying scientific methods.

Answer 6

Because You don't drink it fast enough & like everything else it goes bad when no one drinks it lol