How long can milk be left out of the refrigerator?

Some industry experts caution not to leave milk out of the refrigerator even for the time it takes to prepare, eat, and clear away a meal, although others say that’s conservative.  It’s a good idea to pour the approximate amount you need for a particular meal into a glass or pitcher and put the carton back into the fridge, said dietician Mary Martin Nordness.
 
Off-flavors may develop in a clear plastic container of milk exposed to direct sunlight for as little as a few minutes, and strong fluorescent lights can cause vitamin deterioration in as little as 2 hours, according to Cornell University researchers. However, food scientist Susan Brewer points out that the plastic containers used by most major dairies aren’t clear; they’re translucent. Morevoer, for most meals, there would be no direct exposure to sunlight.
 
Source(s):
Mary Martin Nordness, registered dietician and National Dairy Council Ambassador
Susan Brewer, Ph.D. University of Illinois, Department of Food Science and Human Development
Steven C. Murphy, Senior Extension Associate (Milk Quality Improvement Program)
Department of Food Science, Cornell University
Cornell University Department of Food Science’s Milk Quality Improvement Program Factsheets: “Light Induced Defects in Milk”