After looking at the nitrogen tanks that live on city sidewalks, a reader asked us to look into another city mystery. She wanted to know "Why is the expiration date on milk different for New York City? Does it really take that many more days for the milk to get here?" The NY Times looked into this in another shelf-life (1982), and reported:

New York City is the only place in the state and one of relatively few in the country that has its own dating system for fluid milk, which may legally be sold only up to 96 hours after 6 A.M. on the day after pasteurization. The rule is the same for whole, skim or low-fat fortified milk.

According to Charles Reisberg, Assistant Commissioner of the Department of Health, the four-day period should allow the consumer three additional days during which the milk will remain in good condition. ''We know that at seven days after pasteurization there is a lessening in quality, even with milk properly refrigerated at 45 degrees,'' he said.

Outside the city limits the processer determines the expiration date.

More recently, NYCnosh looked into the milk mystery and theorized that "if you purchase your dairy products from a 24-hour corner store or major chain grocery (places where someone is always around to accept delivery shipments) and bring it home right away, you are likely to have avoided any extended period of non-refrigeration and might want to use the later date as your guide."

This message board points to a statement made by John Gadd, a spokesman for the city's Department of Health, who says that milk shipped to New York is more likely to stand unrefrigerated for brief periods. "It's one of those uniquely New York sorts of things. In other parts of the country, the expiration date is often 11 or 12 days after the date of pasteurization, but our experience and research have shown that here, 9 days is a reasonable threshold." Henry Beyer, a spokesman for New York State Dairy Foods, disagrees! He says that refrigeration and processing practices have improved since the nine-day expiration date was introduced.

Who knew milk could be so controversial! We're just happy if we can find a carton that isn't expired at the bodega.

Photo via NYCnosh.