Usually, it takes about 4 hours for milk to be transported to your doodhwallas (milk delivery people), who then add water to it, and sell it on to their customers. Average time for milk to go from cow to the customers is 6 hours. By most dairy standards, this milk is already unfit for human consumption.
Customers in India usually know that their milk is mixed with water, and are happy about it because the day's milk is boiled before each use. At the end of the day in the average household, the last bit of milk has been boiled about 4-5 times. It's used to make paneer and ghee (spelling?)
By this time, the milk has a slightly burned/sugary taste, and is a little brown in colour.
The milk that IS distributed in pouches only counts for about 15% of milk in India. From experience, I can tell you that finding a "clean" dairy is rare (the cleaning chemicals are not cheap), and that the pasteurization process used isn't always as good as it can be. Also... the distribution of the pasturised packs is Ambient temperature again. This gives the milk a good head-start on the way to "going off".
At this point, It is important to understand what Pasteurization does.... it kills active bacteria - stuff that damages the milk, and eventually takes over the milk causing it to "spoil" and "go off". Taste is important too. Pastured milk tastes very like milk from a cow. Approximately 10% of Indian milk is buffalo milk. This stuff is hard to deal with, and the pasteurization process is less reliable. Pasteurization does NOT kill the bacterial spores. These are like bacteria "seeds", and will produce more bacteria if the conditions are right. In India, the conditions are nearly always right.
The alternative is UHT treatment. "Ultra High Temperature" pasteurization is a very precise process that isn't used much at all in India, mostly because it "tastes wrong" and is very very white. both the colour and taste are not trusted by the average Indian. If you tell someone that the milk will last in the package "for over a year" they usually assume that there are nasty chemicals in it.
UHT treatment - very importantly - kills the spores. If you then put your milk in the right kind of container, it will last for a very very long time.
For Indian customers, Taste is very important. Also, Tradition is very important. You have a trusted doodhwalla, you're going to get your milk from him. Daily.
IF you're a your "new generation" Indian, chances are you buy your milk in a plastic pouch and put it in the fridge. The problem is, your pasturised milk has already had plenty of opportunities for the spores to produce bacteria, and your pouched milk is a ticking clock.
TL DR: In the US and Europe, and a tiny bit of India, Milk is collected, pasteurized, packaged and sold. In MOST countries, the milk is cooled the moment it leaves the cow, and stays cold until the customer drinks it. In India, the milk has a lot of time "warm". Even after being pasturised it gets warm here and there. This dramatically reduces the lifetime.
For more reading google "India and the white revolution" and "The Second white revolution". These poorly named movements are about milk... not skin colour.
Fun Fact: about 70% of ALL milk produced in India, comes from "farmers" with 3 or fewer cows.... Now imagine the trouble of organizing such a situation.
Source: Written by 'Chuff_Nugget'.