Intresting on hub:

how to Make a Battery From a Lemon? APPARATUS : 18-gauge copper wire (smaller gauge will work too, but 18-gauge is stiffer) Wire clippers Steel paper clip (Some people find that a 2-inch strip of zinc works better) Sheet of coarse sandpaper Lemon Help from an older friend or an adult PROCEDURE:
Have your older friend or an adult strip 2 inches of insulation off the copper wire. Clip the 2 inches of bare wire with the clippers. Straighten out the paper clip and cut about 2 inches of the straightened steel wire, or use a 2-inch piece or strip of zinc. Use sandpaper to smooth any rough spots on the ends of the wire and paper clip or piece of zinc. Squeeze the lemon gently with your hands. But don't rupture the lemon's skin. Rolling it on a table with a little pressure works great.
	Push the pieces of the paper clip and the wire into the lemon so they are as close together as you can get them without touching. Moisten your tongue with saliva. Touch the tip of your wet tongue to the free ends of the two wires. You should be able to feel a slight tingle on the tip of your tongue and taste something metallic
sources:  http://www.energyquest.ca.gov