A recent increase in the prices of fine and rare wines has motivated dishonest wine sellers to refill old bottles with inferior vintages. Opening even one bottle of a rare wine for testing can cost tens of thousands of dollars, because the contents are exposed to the atmosphere.

Simon Fahrni and colleagues, University of California, Irvine, USA, reported a proof-of-concept study for sampling and testing the “angel’s share”, the gas phase at the top of a bottle of wine, collected from the wine cork.

The researchers used accelerator mass spectrometry to measure carbon-14 levels in gas samples from 32 wines produced between 1934 and 2006. They compared their results to historical records of carbon-14 levels in atmospheric CO₂, which surged during the 1950s and 1960s as a result of open-air nuclear weapons tests, and gradually declined after these tests were banned.

Accurate vintages were obtained for 23 of the wines. Five wines yielded insufficient gas extract samples, and four yielded anomalously low carbon-14 levels. Because the wines were very valuable, the bottles were not opened to collect liquid samples, and the cause of the anomalies was not determined. The researchers also point out a need to study isotope fractionation as a result of diffusion through the cork.

• Angel’s Share Combats Wine Fraud: ¹⁴C Dating of Wine without Opening the Bottle,
  Simon M. Fahrni, Benjamin T. Fuller, John R. Southon,
  Anal. Chem. 2015.
  DOI: 10.1021/acs.analchem.5b01998