Making batch 80 match batch 1
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A customer who liked the last bar expects this one to be the same, and a shop buyer requires it.
The thing that loses accounts
Not a bad batch. A different one.
A bar that is a shade lighter, smells weaker, or feels different is a complaint even when it is perfectly good soap.
And in a handmade craft, variation is the default state unless something is actively holding it.
Where variation comes from
Oils: a new lot, a new supplier, a slightly different SAP value.
Fragrance: reformulated by the supplier, or a different lot with a different strength.
Temperature: the same recipe poured warmer gels and poured cooler does not, and gel changes color and texture visibly.
Trace: poured thin or poured thick changes the swirl and the top.
Cure conditions: a humid month cures differently from a dry one, and weight and hardness follow.
Controlling it
A written process with numbers: temperatures, ratios, times, not descriptions.
One supplier per material, changed deliberately and tested when it changes.
A deliberate gel decision every time rather than whatever the room did.
The same mold, the same depth, the same cut.
And a retained bar from every batch, kept, labeled, so you have a physical reference rather than a memory.
Checking it
Compare the new batch against the retained bar: color, scent, hardness, weight.
Weigh a sample at the end of cure rather than trusting the target.
And when something has drifted, go to the batch record rather than guessing, which is the entire reason for keeping one.