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I left milk out in a jug, bought brand new, for twelve hours. Is it still safe to drink?

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    Why would you risk food poisoning for $3.50? – rfusca Feb 20 '15 at 14:43
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    You can save it for baking/cooking, but I wouldn't drink it. Milk is pretty close to broth when it comes to pathogen friendliness. – Mr. Mascaro Feb 20 '15 at 14:49
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    Although probably not classed as safe however I quite often, through sheer laziness, leave milk on my counter at home all day (I drink a lot of coffee) and I've not been ill yet.. – Doug Feb 20 '15 at 16:29
  • Doctors quite often (but not always) survive ebola epidemics. Does that mean it isn't serious enough to warrant caution? – LabGecko Mar 12 at 13:31
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Dairy is something of a special case because the natural bacteria in dairy products will tend to outcompete any interlopers...In short you're more likely to end up with a kind of redneck buttermilk (from the action of natural Lactococcus lactis or Lactobacillus bulgaricus) than something that is toxic to you. So unless the milk was already contaminated with something not normally native to dairy, you should be fine. The taste will likely have gone substantially off though.

Note: we are assuming that the milk was pasteurized. Raw milk is prone to contamination with things like listeria and e. coli, and those would certainly cause you some upset.

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    Contamination also tends to occur after the seal on the milk has been broken. Which might mitigate the chance of contamination, but even so, 12 hours is pushing it quite far. – Zibbobz Feb 20 '15 at 17:57
  • that being said, and I make yogurt and sour cream when I feel like it, when that process does grow the wrong culture(s), it can make you really ill. I had a yogurt culture I kept going for months, and one time I guess my hygene wasn't perfect and the yogurt made me painfully ill (at least I believe it was the yogurt). – Escoce Feb 20 '15 at 17:59
  • @zibbobz: The thing is, whatever gets into it is going to be fighting the regular milk bacteria for resources, and the milk stuff is going to have a HUGE head start. You'd have to have a significant colony that is proportionate to the milk stuff. – Satanicpuppy Feb 20 '15 at 19:21
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    I'm not sure I understand this answer. You say you are assuming the milk is pasteurized. But if the milk is pasteurized, that process will have killed off the "natural bacteria in dairy products." Bad bacteria (e.g., Listeria) will grow faster in pasteurized milk rather than raw milk partly because it is lacking those "natural bacteria" you mention. On the other hand, as you point out, raw milk is more likely to be contaminated in the first place. But if anything bad is in pasteurized milk (which sometimes happens, which is why we refrigerate it), it will generally grow faster. – Athanasius Nov 18 '15 at 23:08
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    Yes, "normal" pasteurization doesn't sterilize, but it certainly reduces milk bacteria population. Bad bacteria thus grow faster without as many natural bacteria as would occur in raw milk. Studies generally indicate that somewhere around 0.5-1% of pasteurized milk samples are "contaminated" (probably after pasteurization) with bad things like Listeria, and they will grow much faster at room temperature and could cause illness. Raw milk samples have a much higher incidence of contamination (over 10%), but your Lacto competition argument is more relevant there. – Athanasius Nov 19 '15 at 23:16
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I would...with milk you generally can tell the moment it comes near your nose or touches your tongue whether it's gone bad or not.

That doesn't mean I would serve it to others, that's risking someone else's health.

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    You should NEVER, EVER have to rely on taste or smell to determine if something has gone bad. This is dangerous advice. Asking someone to use their olfactory senses to test for spoiled milk is a very risky path. – yuritsuki Feb 20 '15 at 20:26
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    @thinlyveiledquestionmark - nuts. What else should one rely on, if not an "expert" on the produce in question? Course you can fail pretty badly, but IMHO in the case of whole cow milk I think it's a pretty good advice. (And certainly better than blindly relying on any best before dates.) – Martin Feb 20 '15 at 21:15
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    @Martin The entire point is that your nose is not an expert. There are all kinds of dangerous bacteria that produce nothing at all that you can smell. So as you say, you can fail pretty badly - and in the world of food safety that means you can get really sick. – Cascabel Feb 20 '15 at 21:23
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    Those are sell by dates... – Escoce Mar 9 '15 at 19:16
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    Ancient discussion, but... I'm with Escoce on this one. Milk's one of the more delicate things you buy at the store, and not all milk is shipped or stored identically, making sell-by dates and guidelines pretty unhelpful, I've opened "fresh milk" that I couldn't drink. I also had a quart of milk that went sour in 45 minutes as I was drinking it. Once milk is open, especially, the amount of time it's safe to drink is a crap-shoot based on environment, and your nose/tastebuds are the best judge at that point. Guidelines don't know where you live or how often you ferment things on purpose. – kitukwfyer Jun 21 '17 at 14:18

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