We’ve all taken a swig out of a milk carton that’s a couple days past its expiration date, with little to no consequences.

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Which makes us wonder: Do these dates really mean anything?

“Expiration dates are something people find confusing and with good reason,” says Don Schaffner, Ph.D., a professor of food science at Rutgers University. “There are expiration dates, best-by dates, best-before dates—and there’s not really a lot of standardization around what those all mean.”

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In fact, Schaffner says expiration dates are mostly based on product quality, not contamination risk, and often they’re set by legislation that’s not always based on the best scientific evidence.

For example, milk produced in Schaffner’s state of New Jersey has one expiration date if it’s sold within the state, but that same milk is stamped with a different expiration date if it’s sold just across the state line in New York.

Still, while there are some Expiration Dates You Can Totally Ignore, there are some drinks that food scientists just don"t take chances with.

Here’s what they say could turn potentially dangerous.

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E. coli is the pathogen most commonly associated with unpasteurized drinks, but it’s not the only one.

“Unpasteurized milk can support listeria growth, even in the refrigerator,” says Kathleen Glass, Ph.D., associate director of the Food Research Institute at the University of Wisconsin-Madison.

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Pasteurization kills pathogens by heating up milk (and other beverages) to a temperature higher than that which bacteria can withstand.

According to the International Dairy Foods Association, this was traditionally done in a giant vat, where milk was heated to 145 degrees for 30 minutes.

These days, the more common technique is high-temperature, short-time pasteurization, which cranks up the heat to 161 degrees for 15 seconds, followed by rapid cooling—which kills potential pathogens and makes beverages much safer to drink.

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Related: Is Raw Milk Safe To Drink?Interestingly, unpasteurized apple cider, which ferments over time, may actually become safer past its expiration date.

“If your apple cider was contaminated with E. coli,” says Schaffner, “the bacteria would actually die faster at room temperature because the cider would turn to alcohol and kill it.”