Please remind me, what metal interacts badly with the acid in tomatos?

Aluminum

@marinelife Thank you! I had a feeling that was it, I don’t know why I doubted myself. I appreciate you taking the time to answer such a simple question.

Reminder to self – don’t use aluminum to make marinara!

Except in the UK (and maybe Canada and other outposts of the Empire), where it’s aluminium.

Aluminum and there is a debate about cast iron.
Are there any types of food that are not recommended to be cooked in cast iron cookware?
Foods which are very acidic (i.e. beans, tomatoes, citrus juices, etc.) should not be cooked in a cast iron utensil until the cookware is highly seasoned. The high acidity of these foods will strip the seasoning and result in discoloration and metallic tasting food. Wait until cast iron is better seasoned to cook these types of foods. source

Another source

@wilma Thanks for making me remember that, some years ago, I was making a pot of chili using a cast iron pot. It involved plenty of tomatoes and ended up having a very metallic taste to it. I never again made chili in cast iron. I guess that pot wasn’t “seasoned” enough.

Natrium
Though, it actually reacts with the water in the tomato.

When I put aluminum foil on anything like lasagna it actually eats holes in the foil