Yeast and sugar generator can power cellphones, but how does it work?

This yeast-and-sugar powered generator invented by Dr. Cedrick Ngalande of Malawi can supposedly power cellphones, OLPCs, and medical devices for up to eight hours, but apart from a few vague guesses involving CO2, oscillating motion, and a couple Sharper Image desk toys we've got lying around, we're utterly at a loss to explain how it works. Ideas, leave 'em in comments! [Via Afrigadget]