Where and how you store milk is crucial to maintaining its quality. According to the U.S. Food and Drug Administration (FDA), milk left unrefrigerated for more than two hours is unsafe to consume.
Milk should be stored on the coldest interior shelves of the refrigerator, not on the door shelves. It should be kept at 38° to 40°F (1.5-4.5°C) in its original container, away from the door.
When milk is stored on the refrigerator door shelves, it is exposed to warm air every time the door is opened, which encourages bacterial growth.
The coldest parts of the refrigerator are the back and bottom. Just make sure the refrigerator isn't too cold, or the milk will freeze.
Also, make sure to keep the lids on milk cartons tightly closed. This helps reduce contamination and odors from other refrigerated products.