Rare wine attracts counterfeiting because the product is consumed and the evidence destroyed. Salerooms have built a layered verification process in response, and no single element of it is decisive alone.
The paper trail comes first
Consignments are assessed on where the bottles came from before anyone examines the glass. An unexplained source is the strongest warning available, and it costs nothing to check.
Documentation from a producer, a merchant or a storage facility establishes a chain, and gaps in that chain are where scrutiny concentrates. A single unaccounted decade is enough to stall a sale.
Houses decline consignments on provenance grounds alone, which is a commercial decision as much as an ethical one given the reputational exposure.
Physical examination of the packaging
Glass manufacturing methods, seam patterns, base profiles and embossing all changed over time, and a bottle inconsistent with its stated period is immediately suspect.
Labels are examined for paper stock, printing method and ageing pattern, since artificially aged paper rarely matches the uneven staining of genuine cellar time.
Capsules, their metal composition and the way they were applied provide a further set of period-specific details that are difficult to reproduce convincingly.
The cork carries independent evidence
Corks are usually branded with the producer and often the vintage, and the branding style changed over the decades in traceable ways.
A cork can be examined without opening the bottle in some cases, and its condition should be consistent with the fill level and the claimed age.
Mismatches between cork, label and fill are among the most common tells, because a forger has to get every element consistent simultaneously.
Producer records close the loop
Estates hold records of what they made, in what quantity and in which formats, and a bottle claiming a format never produced is settled quickly.
Some producers maintain reference collections and will inspect suspect bottles directly, which is the most authoritative check available.
Total production figures also constrain the market, since the number of bottles circulating cannot exceed what was ever filled.
Why the process remains imperfect
Sophisticated counterfeits use genuine old bottles refilled with other wine, which defeats every test based on packaging.
Chemical analysis of contents is possible but requires opening the bottle, which destroys the item being authenticated.
The practical defence is therefore concentrated on provenance and market structure rather than on forensic certainty, and buyers of the rarest wines accept residual risk.