My Lemon cream has a metallic taste... How do I avoid this?

I have tried making lemon curd using no metal at all, this batch was in a glass bowl heated over water and it still tasted metallic and awful. My roommate, Nick Edgington, who is a chemist said to add baking soda and so I added a teaspoon to the curd and it foamed up like crazy, he said it was reacting to the acidity. So I transferred it to a larger bowl, so it wouldn't foam over and after an hour, I was able to stir it and lose the foam, it's back to being a curd and really doesn't have that taste anymore. He also said that cream would probably work in the same way, but that was after I already added the soda and freaked out a little... so maybe I'll try that next time.

Those being aluminum and copper (stainless is fine). Any chance that's the culprit? A link to the recipe might help diagnose the problem.

I've heard that you're not meant to use certain metal bowls or pans as they impart a metallic taste.