Subject: When all fruits were combined, why'd it produce the same voltage as one?

Our project consisted of 10 different fruits and veggies where we were 
making fruit batteries. We were testing the voltages using zinc and copper 
electrodes and the results were around 0.7 - 1.02 volts. We decided to 
juice the fruits and test them in liquid form which turned out around the 
same. Then, we combined all the fruits together in liquid form and we'd 
expected the voltage to increase to 3.0 - 4.0 volts but the results were 
0.7 - 1.0 volts, as it would be with one idividual fruit. Why didn't the 
voltage increase as we originally thought?

Re: When all fruits were combined, why'd it produce the same voltage as one?