When pasteurized milk goes bad, it’s baaaaaad, says Nyleve. There’s nothing you can do to save it, so just throw it out. There’s a big difference between sour milk and spoiled milk. Sour milk is nutritious and delicious—it’s the natural result when unpasteurized milk is allowed to ferment with wholesome bacteria, much like yogurt. There are many uses for sour milk—and, indeed, you can simulate sour milk by mixing a little lemon juice into pasteurized milk and allowing it to sit for a while. But when milk has been pasteurized, all the good bacteria have left town, and when it goes bad, it’s spoiled. Think of it as a process of decay, rather than natural souring. Do not drink it! Spoiled milk is beyond use. Please throw it away.
Board Link: Should I just throw out the sour milk?