Back to the original question:
Never really paid close attention, but a sibling pointed out that one should not keep a metal spoon in the chrain used to put on your fish more than a few minutes.
While you used the same spoon a few hours earlier to cook with a hot brisket.
Is this in fact something one should avoid? And use plastic instead for the chrain? As it's a davar shebichariv and would be problematic when using for fish?
Whether or not a davar charif makes kavush quickly (the shiur of resicha- boiling) is a machlokes the Mechaber and the Shach.
It is based off a Rosh who gives this shiur for Brine.
The Mechaber learns that this is a "super-charged" kavush because it's charif and therefore applies it to Vinegar as well. However, the Shach learns that it is a "super-charged" melicha that assers the whole thing (not just a k'dai klipa) therefore it does not apply to a davar charif at all. He brings a proof from a diff. Rosh that refer to the shiur melicha for vinegar as being 24hr. The Pr"M brings from the M"A an answer that there's a diff. bet. strong and regular vinegar (in which case a davar charif does make it kavush quickly).
However, the Badai hashulchan (from memory, I don't have it on hand) quotes the M"B (in hilchos pesach) that he is machria like the Shach (And therefore Davar charif plays no role in Kavush).