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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?

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Guess I forgot to mention: regular old pasteurized milk –  Jessica Brown Aug 10 '12 at 14:43

5 Answers 5

up vote 13 down vote accepted

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.

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I agree with your advice. In my experience even if there might be a slight something-more-than-nothing smell on milk which has passed the expiry date (with some significant time), there might be absolutely no taste difference. –  hlovdal Aug 12 '12 at 22:58
    
+1: Got that right :) –  Divi Aug 13 '12 at 9:29

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.

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@Divi, please don't ever post the "follow your nose" advice again. Refer to our food-safety wiki. You can't smell most forms of spoilage; if it smells bad then it probably is, but that doesn't work in reverse. –  Aaronut Aug 12 '12 at 18:36
    
+1: Good answer, there are so many ways to see when its gone bad and at least with milk whenever in doubt, follow your nose :) –  Divi Aug 13 '12 at 9:21
    
@Aaronut: Agreed and I fixed my comment. –  Divi Aug 13 '12 at 9:28

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.

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i left 1 qt non fat and 1 gal full fat milk in my car from fri. afternoon to sat. p.m. I live in Los Angeles and it was probably abt 75 degrees during sat. The milk was far down in the back of my van (probably not in direct sunlite). I quickly tasted it when I retrieved it from the car 7:00 p.m Other than being warm, it was not sour. The next day (cold of course) it tastes just fine. (I did not taste the full fat yet b/c I don't drinkk that in general.) My feeling is that I've only limited the "shelf life" of the milk in my own fridge. mf

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depending on the pasteurization process used, milk can spoil (= be full of nasty bacteria) without going sour. –  rumtscho Feb 18 at 12:19

Milk, being left out that first time takes quite a long time to go sour. But put it back in the refrigerator after being left out for a long time and take it out again, and it will go sour very quickly. In other words, it can be left out 'once'...but not twice.

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Based on observing my neighbor's kids fixing themselves cereal (and not bothering to put the milk back), I have different evidence. As with other issues of bugs multiplying, it's not an issue of how long for each time ... it's cumulative amount of time that they've had to multiply, and you must've hit that threshold on your second time (although, it's not a simple threshold ... just consider it a metaphor). –  Joe Mar 24 at 19:55

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