Why do some (usually vacuum packed) meat products stink when heated? What's in them.

Hi!

We ran into this multiple times. With vacuum packed meats as I remember, probably from Spain. It's not rotten or spoiled and it seems normal when cold. But it has a prominent unpleasant smell.

But when you start to cook them in any way the start to stink. Even hot water is enough for this to become noticeable. Also includes plain fatback ("fat backon" or whatever it's called in English.)

And the stink seems to persist forever. For example rendered fat from it stinks anytime you heat it back up, months later even.