A supplier has issued a withdrawal notice. Which of your batches are affected?

It is 4pm on a Friday. A supplier rings, or an email arrives with a notice attached. There has been a problem with one of their lots — a foreign body, an allergen that was not declared, a positive result on a routine test.

The notice names their lot number. Everything that happens over the next few hours depends on a single question:

Which of your batches did that lot go into?

If you can answer it, this is a contained afternoon: three batches, a short list of customers, some phone calls. If you cannot, you are facing something considerably worse — and worse in a way that costs real money, not just a bad evening.

The expensive answer is “all of them”

When you cannot match the supplier’s lot to your own production, there is only one defensible thing to do: treat everything you made in the plausible window as affected.

That is not a technicality. It means:

• Withdrawing product that was never at risk.
• Ringing customers who did not need to be rung.
• Destroying or holding stock that was perfectly good.
• Explaining to those customers why you cannot be more specific.

The last one is the part that lingers. A trade customer who has just quarantined six weeks of your product because you could not narrow it down remembers that conversation at the next supply review.

And the gap costs nothing to close. It is one number, written down once, at the door.

Why the gap exists at all

Nobody decides not to record supplier lot numbers. It happens for ordinary reasons.

The number is on the carton, not the paperwork

Invoices and delivery dockets carry the product code and the quantity. The lot is printed on the packaging — sometimes only on the outer, sometimes only on the inner bag. Getting it means opening the pallet and looking, which is fine when somebody is standing there with a pen, and does not happen when the delivery lands mid-run.

Your own batch code feels like the important one

It is the number that goes on your label, into your records, onto the customer’s docket. The supplier’s lot feels like their business. It is not — it is the only handle you have when their problem becomes yours.

“One step back” gets read as “know your supplier”

Knowing you buy raspberries from Hawke’s Bay Berry Co is not one step back. One step back is knowing which delivery, which lot, which quantity — and being able to point at the batches it went into.

The lot arrives in a bag that gets decanted

Product goes into a labelled bin and the original packaging goes in the skip, taking the lot number with it. By Wednesday nobody can tell which delivery is in the bin.

Two directions, and most people have only tested one

Backwards — from a finished pack to the ingredients

A customer complains, or a regulator asks. You have a pack in front of you with a date and a code on it, and you need every ingredient lot in it, plus the supplier of each. This one is usually easier, because production records tend to be written forwards and read backwards.

Forwards — from a supplier lot to the customers holding stock

This is the withdrawal-notice direction, and it is the one that breaks. From one supplier lot you have to reach:

• Every batch that drew on it.
• Every bulk bin those batches filled.
• Every pack run drawn from those batches or bins.
• Every dispatch of those packs.
• The named customers holding them, and how much.

Every step is a place to lose the thread, and the loss compounds. Get step two wrong and everything after it is wrong too — in a direction that always overstates.

Where it breaks in practice

Four traps. All four are ordinary; none of them is carelessness.

One batch, two lots

The recipe needs 9 kg and the open bag has 7 kg in it, so you top up from the next one. That batch now contains two lots — and if the record only names the first, the batch is invisible when the second lot is the one under notice.

Recording a partial draw feels fussy at the time. It is the single most common reason a batch gets missed.

One lot, several batches — sharing a bin

The reverse. A 40 kg lot goes into three batches over a fortnight. Two of those batches went into the same bulk bin, and pack runs were drawn from that bin.

Resolve this by hand and you will count the bin twice — once against each batch — and chase more product than exists. Almost every manual exercise overstates for exactly this reason.

The bin is where the chain usually snaps

Returns were never netted off

Quantity dispatched is not quantity at risk. If some came back last month — short-dated, damaged, a customer overordered — the number you are chasing is smaller. Chasing product already sitting in your own coolstore wastes the afternoon.

The fix is at the receiving door

Five fields, recorded once, at the point the pallet arrives:

• The supplier’s lot number — theirs, exactly as printed, not one of yours.
• Quantity received.
• Date received.
• Expiry or best-before.
• Temperature at handover, for anything chilled or frozen.

The lot number is the one that does the work. The rest make the record usable.

Temperature at handover earns its place separately: it is the reading at the moment responsibility changes hands. A cold chain with no reading at that point has a gap exactly where it matters, and “it looked frozen” is not a record.

What good looks like

The notice arrives naming lot HBB-24-0912. Within a few minutes you can say:

That lot arrived on 12 September, 40 kg. It went into three batches. Two went into bin BB-0044, one went straight to a pack run. Between them: five pack runs, 412 units dispatched net of returns, across four trade customers — and 60 units through our own online shop.

That last clause is doing quiet, important work. Four trade customers is a ring-around. Sixty units in the hands of the public is a different kind of event — a public notice, with MPI involved. You need to know which one you are in before you start making phone calls, and the only thing that tells you is whether your dispatch records separate trade from consumer.

Notice too that the answer is smaller than “everything we made in September”. That difference is the whole return on writing one number down at the door.

The companion guide covers what the exercise should leave behind once you have resolved the scope — the records a verifier actually asks for.

How BatchIQ handles it

Stock receiving asks for the supplier’s lot number as a first-class field rather than a note. Frozen and chilled ingredients also ask for the handover temperature and check it against the limit before the receipt saves, so you are told the delivery is too warm while the driver is still there.

Batches draw down specific lots, and the stock check is per lot rather than per line — 5 kg plus 5 kg out of a 7 kg lot is refused even though each line looks reasonable on its own. When you are short, you add a second line against the next lot, and the batch record then names both. That choice is frozen into the record, so renaming or retiring an ingredient next year cannot rewrite what went into a batch made today.

Search any code — supplier lot, batch, bin, pack run or dispatch — and walk the chain in either direction. Resolving forward from a lot, bins resolve once, so a lot split across batches that shared a bin is not counted twice. Quantities come out net of returns, and trade and consumer channels stay separate.

That is the whole product, really. The rest of it exists to keep that one chain unbroken.