Does the mentos and Diet Coke experiment need cafine?

The classic Mentos and Diet Coke experiment does not specifically rely on the presence of caffeine for producing its characteristic eruption. While most often performed using Diet Coke, which does contain caffeine, the reaction and subsequent foaming occur primarily due to the interaction between the dissolved carbon dioxide in the soda and the nucleation sites provided by the rough surface of the Mentos candies.

When dropped into the soda, the Mentos serve as ideal nucleation sites for the rapidly dissolved carbon dioxide gas to form bubbles. This sudden and abundant nucleation process creates a massive release of bubbles which builds up pressure within the bottle, eventually leading to the iconic eruption of soda and foam out of the container. It is this nucleation effect induced by the physical properties of the candy, rather than the presence of caffeine, that causes the distinctive reaction in the mentos and Diet Coke experiment. So, no, caffeine is not necessarily required for the experiment to work, although Diet Coke happens to contain it alongside other ingredients commonly found in cola-type beverages.