How long does it take for milk to spoil unrefrigerated?

Question

A half gallon of milk (in the paper carton, not plastic) got left in the car for 1.5 hours in about 80 degree (~27 °C) weather (evening so no direct sunlight). Is it still probably safe to eat if one has a strong stomach or pretty risky? Any particular signs to watch for to indicate it is no longer safe? Carton bulging? Off smell? Etc? How quickly will milk spoil (unopened) in warm summer weather like that?

Answer 1

I don't think anything will be wrong with that milk.

1. If it's fresh milk, which I doubt, you should consume it in less than three days.
2. If it's pasteurized milk, which is much more likely, it'll be unaffected.

Signs of spoilage are a sour smell and sour taste. You should make a habit of always smelling your milk (food) before drinking (eating) it. If it doesn't smell like you'd expect, taste it. If it doesn't taste like you'd expect, ditch it.

Milk is cultivated with lactobacillus, a bacteria that's beneficial for us. So, even though milk may taste sour, it doesn't mean that it's undrinkable. In Holland, there's sour-milk (karnemelk), that some people consume (I don't like it, myself).

Under the right circumstances, milk will turn into yogurt, thanks to the lactobacillus...

At any rate, if in doubt, throw it out.

Answer 2

Whatever kind of milk it is, it should be OK for a couple of days, and it will still be usable for most purposes when it has developed a slight sour smell.

When I was young we didn't have a fridge, milk would last a day and a half to two days in hot weather, longer if the bottle was wrapped in wet newspaper. The first sign that it is going off - you notice floating white specks when you put a splash of milk in your tea or coffee. Then you notice a slight off sour smell. The milk is still useful, but close to the point of curdling.

It never gets dangerous, just doesn't do what you expect after it has curdled.

Answer 3

I like milk in any state. 1.5 hours for in paper carton would do no harm for pasteurized milk. It takes 2 or 3 days for milk to go sour. First it becomes of sour taste, being still liquid. It's safe to drink it, but it's not tasty. Wait until it become curdled, and either drink it, or warm in a pot (but not boil), filter out thrusting, an you'll get nice farmer cheese. It is good alone, or mixed with sour cream.