This was Namagomi's idea, so the resultant hijinks can all be traced back to him.
Partly a spoof of Jolt Cola, and partly fulfilling an apparent need for Gaeran energy beverages, Volt Cola was invented by Chandler Sablemech. It's a carbonated soft drink vaguely like rootbeer that also contains a large number of herbal stimulants. Some have suggested that the taste is roughly analagous to a mix of Coca-Cola and espresso.
Volt Cola was also a key commodity in the initiation of trade with the Tuathan Druids.