Very frequently in the Aramark-contracted mess hall here at The
Citadel, I find a taste in some of the food--the best way I can
characterise it is almost metallic, but also (i think) resembling the
formaldehyde that I've smelled dissecting animals in a biology lab. It
is most frequent in food that I am almost certain is canned- ravioli
(usually), chicken and dumplings (almost always), spaghetti (about
half the time), beef stew (usually), etc. I also associate the same
taste with foil-wrapped tuna.

I don't know what the taste actually is, whether it is spoilage or
excess of some kind of preservative.

My question is: what substance (and if applicable, what process)
causes that taste ?

I know that it is difficult to answer a question based on a particular
taste, but I hope I have provided enough information that the question
is answerable. Thank you.