When stock goes off-condition
Updated
A cured bar keeps for a long time, and it does not keep indefinitely, and the way it fails is not the way food fails.
Soap does not spoil, it degrades
There is no microbial spoilage to worry about in a true bar soap: the pH and the low free water make it an inhospitable place.
What degrades is the oil in the superfat, which oxidizes. And the fragrance, which fades.
So an old bar is not unsafe. It smells of nothing and it may smell faintly of old oil.
What to look for
Dreaded orange spot: small rust-colored specks that appear over months and spread. It is oxidized oil, and it is the standard sign a bar has been kept too long or was made with an oil past its best.
A rancid smell, which usually accompanies it.
Fragrance gone, which is a commercial failure rather than a safety one.
And bars that have absorbed moisture and gone soft, which is a storage failure.
Rotation
Which is entirely a record-keeping job: batch and date on every case, oldest stock forward, and an actual count rather than an impression.
A maker with six fragrances and no rotation accumulates a slow-moving scent that ages out while the popular one is remade weekly.
Six months to a year is the practical window for a bar at its best. Much longer and the fragrance is the first thing customers notice missing.
What to do with it
Spotted or rancid bars: do not sell them, at any price. That is the scrap line.
Faded but sound bars: usable, honestly described as unscented or lightly scented, or given as testers.
And then go back a step: DOS usually points at an oil that was already old when it went in, or a superfat set higher than the oils can carry.