I've had it for more than ten days and it is just fine. I save it up for cheesemaking, and if I put it in a very clean one gallon jar and put the full jars in the back of the fridge where it is colder, they keep better. Also, the cream that rises to the top tends to protect it, too. So try not to move the bottles once they are full.
I had a quart go bad overnight once, I guess the bottle wasn't as clean as I thought it was, since the other quart bottle from the same milking was just fine for several days.
The only other sour milk was a quart given to a friend, she later admitted that she was so excited to get it that she took a gulp right from the bottle on the way home. So it also got contaminated.
Even sour milk has its uses, though, for baking, or as chicken food.
The key is to have everything nice and clean. I don't obsess....I let the dishwasher disinfect my jars, but I bleach my strainer (I use a re-usable coffee filter, the gold wire kind) just before using it each time. I bleach it with a mild solution (1/2 Tbsp Clorox to 1 cup water) just before I go milk each time, pouring the bleach solution over both sides of the filter.
eta: we only use raw milk here, that might make a difference, too, since it contains good bacteria that are protective.
i think i've had mine in the fridge at least 10 days - you can tell immediately. but as above, just give it to the hens, dogs, or pigs.
but mine doesnt last long. i strain then freeze in wide mouth quart jars.. then take them out as needed. if i time it just right i can have an afternoon 'goat-upcinno' with leftover coffee from the morning.
It lasts a couple of weeks in the fridge for me. I have also found (by accident) that it stays drinkable after about two days on the counter at room temperature! We had a refrigerator go out and we didn't notice for a few days because it's just an extra one we keep in the garage for milk and cheese....the milk was room temperature for about 3 1/2 days before it went sour, and even then it wasn't disgusting, but sort of like buttermilk. Not that I recommend not refrigerating your milk!
Over a week in my experience. I made buttermilk last night that I had to stash behind some peanut butter jars to sit for 12 hrs otherwise DH would assume that I had "left" it out and poured it down the drain.
I just had some this morning that was perfectly fine, and it was dated Feb 9. It's Feb 27 today. It wasn't even slightly off, and it was kept in the door, the warmest part of the fridge.