How does yougurt turn sour when you put a metal spoon in it for too long?
Sounds, like a good experiment.........
And it's an experiment you could do at home.....Take four pots of yoghurt, place a stainless steel spoon, place aluminium foil in the second, and place coper rod in the third. The fourth you leave open WITHOUT sticking metal inside the pot; this serves as the control. Do they taste different?