A spokesperson told the New York Times: "Despite the speculation, there is no secret formula to our recipe. We're delighted to hear that our customers enjoy drinking our Coca-Cola."
McDonald's also ensure that both its syrups and drinks fountains are kept ice cold and refrigerators are insulated front-to-back in order to keep the water chilled and maintain a superior CO2 level.
This means the water is more carbonated, the higher quality soda water making for a crisper taste in the fizzy beverage.
On the McDonald's website it also states: "The water and Coca-Cola syrup are pre-chilled before entering our fountain dispensers with the ratio of syrup set up to allow for ice to melt.
"We also keep our fountain beverage system cold so your drink can always be at the peak of refreshing."
A high-end filtration system is also apparently key with McDonald's noting: "In order to ensure our drinks are always meeting a gold standard, we have proper filtration methods in place."
The final piece of the puzzle is the straw, which McDonald's revealed is slightly wider than usual straws.
"...so all that Coke taste can hit all your taste buds."