Fruits contain acids that act as salt bridges to conduct electricity. Electricity is conducted by transferring electrons in a chain from one point to another to produce current. The acids found in fruits and vegetables, such as the citric acid in citrus fruit, help facilitate this electron transfer.
The study of electricity and chemistry is known as electrochemistry and includes electrical conduction and production. The specific reaction that occurs in fruit that allows it to conduct electricity is an oxidation-reduction reaction, also known as a redox reaction. In redox reactions, electrons are transferred from one compound to another. When this process is repeated in a chain series, electricity is produced.
The two types of cells that can facilitate electrochemical redox reactions are galvanic cells and electrolytic cells. Galvanic cells are spontaneous and are used as batteries, while electrolytic cells are nonspontaneous and require electricity to initiate the redox reaction. Both types of cells have two oppositely charged electrodes known as the cathode and anode that facilitate the oxidation and reduction reactions independently.
The fruit battery experiment that demonstrates the electrical conductivity of fruit is simulating a galvanic cell. Just like any galvanic cell, two galvanic metal electrodes and conductive wiring connected between the two points is required to produce an electrical current.