For one of the forthcoming workshop at MERL, we might explore how potatoes can produce energy using a setup similar to this, and demonstrate that you can do more with a potato than boil it, mash it or make chips (french fries, if you are not from UK). The images below show the simple battery setup using a zinc plate and a copper plate with a small gap between them.
A potato (or two in this case for a larger current) is placed across the plates:
The current measured across the plates was about 160uA:
The next stage of development will be to drive a set of LEDs to indicate the current generated.