Herrings put into a tub with salt or brine, later spitted on sharp wooden spits, and hung up in a chimney to be smoked and dried. Such preserved fish would keep for months (and indeed they were transported in barrels to provide protein on long sea voyages) but were inedible in this state and needed to be soaked to soften them and remove the salt before they could be cooked.
Do I smell a rat?
One key characteristic of red herrings, apart from their colour, was their strong smell, so much so that one use for them on occasion was to train hounds to follow a scent.
a deliberately misleading object
Neither fish nor flesh, nor good red herring