Coke geyser - Part 2

Continued...

A 2006 episode of the television show MythBusters[2] concluded that the caffeine, potassium benzoate, aspartame, and CO2 gas contained in the Diet Coke, in combination with the gelatin and gum arabic ingredients of the Mentos, all contribute to the jet effect.[3] In addition, MythBusters theorized that the physical structure of the Mentos is the most significant cause of the eruption due to nucleation. MythBusters reported that when flavored Mentos with a smooth waxy coating were tested in carbonated drink there was hardly a reaction, whereas standard Mentos added to carbonated drink formed an energetic eruption, affirming the nucleation-site theory. According to MythBusters, the surface of the mint Mentos is littered with many small holes, allowing CO2 bubbles to form very rapidly and in great quantity, in turn causing the jet of foam. This was further supported when rock salt was used as a "jump start" to the reaction

A paper by Tonya Coffey, a physicist at Appalachian State University in Boone, North Carolina goes into detail on the reasons and physics behind the reaction.