What goes wrong

It went rancid

Updated October 2026

On this page7

What it smells and tastes like The four causes, in the order to check them It is not a safety failure Why the batch code decides what you do next The fix is upstream and it is boring Check your own storage before blaming the supplier References

Rancidity is the default failure here and it is a storage and sourcing problem far more often than a bottling one.

What it smells and tastes like

Descriptions vary and the useful ones are concrete: crayon, putty, old nuts, cardboard, candle wax. It is easier to notice against a fresh reference than on its own, which is an argument for keeping a known-good bottle to compare against rather than relying on memory.

The four causes, in the order to check them

The oil was already old. Check the pressing date against the lot. This is the most common and the least visible.
Light. Clear bottles on a lit shelf for months. Check where retail stock actually sits.
Heat. Storage near a heat source, or a summer in a vehicle or a warehouse.
Headspace. Underfilled bottles, or stock that was decanted from a part-empty bulk container.

It is not a safety failure

Rancid oil is unpleasant rather than hazardous, which sounds like a consolation and is not: the cost to a product with your name on it is the same as a safety failure, and the buyer’s response is identical.

Why the batch code decides what you do next

If the cause was the starting oil, every bottle from that lot is on the same trajectory and most have simply not arrived yet. If the cause was one retailer’s window, it is that retailer’s stock. The lot link is the only thing that separates those two, and it is the difference between replacing a case and replacing a season.

The fix is upstream and it is boring

Buy fresher oil in smaller quantities, bottle into something that blocks light, fill properly, and print a date you have actually tested against. None of that is clever and all of it works.

Check your own storage before blaming the supplier

Bulk oil held in a part-empty container in a warm room ages faster than the same oil in a full one, and that is your doing rather than theirs. Decanting into smaller containers as a bulk supply is used down is unglamorous and it is one of the few genuinely effective things a bottler can do to a product they did not make.

Keep a reference bottle from each delivery, tasted when it arrived and noted. Without one, the question of whether the oil came in tired or went tired on your shelf has no answer.

References

United States Department of Agriculture, Agricultural Marketing Service. United States Standards for Grades of Olive Oil and Olive-Pomace Oil, 7 CFR 52.1531 to 52.1542, published at 75 FR 22363 and effective October 25, 2010. Voluntary standards issued under the Agricultural Marketing Act of 1946. ams.usda.gov

Written from federal regulation, voluntary USDA grade standards, FDA labeling policy and published extension guidance, not from a laboratory. The infused-oil pages describe a real botulism hazard and are a starting point for a conversation with your state department of agriculture and a process authority, not a determination that any method you use is safe.