In 2006, an episode of Mythbusters (one of a popular program from the Discovery Channel) found that caffeine, potassium benzoate, aspartame, and CO2 which is contained in the coca cola diet arabic and gelatin as well as material from the mentos causes the effects of "jet" or explosion when mixed .

In addition, Mythbusters concluded that the physical structure of mentos is the most influential of the blast.  When the  fruit taste mentos was slowly  test with carbonated water, no reaction occurred. But when the standard mentos (mint flavor) was added to carbonated water, then generate small explosion.
They add and confirm the theory of the blast.  According to Mythbusters, the surface of the mentos mint covered with many small holes that make the CO2 bubbles are formed very quickly with the number of lots, which causes the explosion "jet" it happened.

This theory is also supported when the solid salt is used as a substitution (replacement) of mentos and a bit of alcohol or liquor of various kinds can also cause the explosion occurred.

Source:
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