After crossing the bricked finish line on Sunday, the winner of the Indianapolis 500 will drive into the winner’s circle, be presented with a celebratory wreath and take a swig from a cold bottle of milk. The latter is one of the grandest traditions in sports, but also one of the most confusing. Why milk? Why is it in a bottle? And (this one was actually asked by a girl I knew in college) has it been sitting in the sun all day?

After solving mysteries in Beijing, Boston and Augusta, GA, the old Y! Sports investigative unit is here to answer all your questions in order to solve the mystery of the milk-drinking drivers. It all started in 1933. After Louis Meyer won his second Indianapolis 500, he requested a cold bottle of buttermilk to quench his thirst. The Yonkers, NY native had grown up drinking the beverage and favored it throughout his racing days.

Three years later, Meyer won his third title and, again, he requested a cold glass of buttermilk to celebrate. This time, a newspaper photographer snapped a photo of Meyer taking a swig from the bottle while holding up three fingers, one to represent each of his Indy victories. The shot would appear the next day in a number of newspapers.

As legend has it, a local dairy executive saw the photo and, realizing a great marketing opportunity, vowed that milk would be given to the winner the following year. (They had thought Meyer was drinking regular milk, not buttermilk.) Except for a stretch from 1947 to 1955, milk has been presented at the Indianapolis Motor Speedway ever since.

Today, instead of buttermilk, the winner is given a choice between whole milk, two percent and skim. Those bottles are held in a cooler by two selected Southern Indiana dairy farmers and are etched with the words “Indianapolis 500 winner,” making the bottles not just a beverage receptacle but a trophy in their own right. The drivers seem to like the milk, not just for what it represents, but because of its taste as well.

Dario Franchitti said in 2007 that the milk is: “Good. Really good. They chill it and it's very cold. I went for full fat inside and then I went outside in Victory Circle after the rain stopped and I had another bottle and I think that was 2%. That was good as well. I was liking the milk.”

Personally, I can’t imagine that milk is the ideal beverage to consume immediately after finishing a grueling three-hour race run at 200 mph in cramped, often-sweltering conditions. But for the racers at Indianapolis Motor Speedway on Sunday afternoon, no drink would be finer. Thanks to the Indiana Dairy Council for helping solve this mystery. We’ll be raising a tall glass of skim in their honor this Sunday.

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Related: Indy 500