The Mentos have tiny pits, or nucleation sites, that provide locations for the carbon dioxide molecules to form. In addition, the gelatin and gum aribic in the Mentos breaks the surface tension making it easier for bubbles to form. Although Mentos has the spotlight, it appears salt may do the trick as well. According to Hyneman, "Plain old table salt is better." Richard Zare from Stanford agrees.
RE: salt by tomtolman :: NR5 :: Show
Here’s the part about salt from the article: