How do I keep a long shelf life of pasteurized milk?

Really long shelf life with pasteurized milk is only able to be achieved with Ultra High Temperature (UHT) processing, typically circa 140˚C for a second or two. 80% of all organic milk sold in the USA is UHT, for the simple reason that the supermarkets wouldn’t carry it unless it had that 6 months ambient temperature shelf life.

Most ‘normal’ milk has a natural shelf life of about 12 to 15 days, depending on whether it is an aseptic filling process or not.

The temperature at which it is stored in your fridge is important. Find the coldest part of the fridge, which will be the bottom shelf, at the rear - not in the door.

Beyond that, you could get creative, and either re-pasteurise it yourself after maybe 10 days. Heat it to 72˚C for 15 seconds. That will kill off any bacteria that are beginning to grow.

Or you could sprinkle in a bit of yoghurt starting culture, and as those “friendly” bacteria grow, they will inhibit other non-friendly bacteria from developing. The impact on the taste would be minimal, and the milk would gain an extra week or 10 days of shelf life - and then it would simply become yoghurt..!