Most dairy can go unrefrigerated for 2 hours before it spoils.
However if the temperature is warmer than 90 F then the dairy can spoil when left out at room temperature for an hour.
If the temperature is 90 F or warmer then the dairy should not be left out longer than an hour but if the temperature is lower than 90 F then the dairy can safely be left out for 2 hours.
Milk can sit out at room temperature for up to 2 hours.
After 2 hours the milk when left at room temperature can begin growing bacteria and going sour and should be thrown out.
Once you buy the milk it should be promptly refrigerated and if you're gonna be awhile before you can get the milk home it's best to place the milk in an ice chest to keep it cold.
Milk left out overnight should be thrown out as well because it likely has spoiled by that time and could contain bacteria that you may not be able to see.
Milk that has actually gone bad will also smell sour and you wouldn't want to drink it anyway.
In general, perishable foods like milk should not sit out of the refrigerator or cooler for longer than two hours.
Cut that time down to an hour in the summer if the temperature reaches 90 degrees F.
After that time frame, bacteria can start to grow.
The FDA asserts that you should never keep unopened milk out of the refrigerator at room temperature for more than two hours.
However, this window reduces as the temperature rises.
This means that when the temperature exceeds 45°F, unopened milk can last up to an hour.
While there are no set recommendations, most research suggests that as long as it's been stored properly, unopened milk generally stays good for 5–7 days past its listed date, while opened milk lasts at least 2–3 days past this date.
If your milk doesn't smell like milk, it's likely expired.
Milk that's gone bad exudes a foul odor — and it will be very obvious upon taking a whiff.
Labuza said this is the best procedure for determining if your milk has gone bad.
"The odor is very obnoxious.