When we light the candle and heat up the junction where the two wires are twisted together, the meter shows that we are generating electricity. As the candle flame blows in the breeze, we can see the meter reading fluctuate. This shows that the voltage depends on how hot the junction is getting. the photo shows a thermocouple made of copper and aluminum, which reached 1.5 millivolts in my candle flame.
The best of the three thermocouples was the one I made from iron and aluminum, shown below reaching 2.5 millivolts. The copper and steel thermocouple read 1.7 millivolts (not shown).