Yes, the demand for a visible "salt bridge" to separate the two half-cells in these fruit and vegetable "batteries" is a source of confusion. Here's another one -- a simple length of copper wire, and an unbent paper are pushed into a whole lemon, 1/4" apart, and a charge is felt across the two wires when touched to the tongue" we've all played with that old trick (at least I hope so, you can try it, if you have the time and materials)"
What happens if the two pieces of metal touch inside the lemon?
What happens if they're set far apart as opposed to 1/4" apart?
Can you guess what the half cell reactions are?
What does a salt bridge really do, and how can a fruit or vegetable do the same thing?