Almost all the carbon dioxide in the atmosphere contains the stable carbon-12 form of the element. Each atom of carbon-12 has six neutrons and six protons in its nucleus. But atmospheric atomic bomb tests, which ended in 1963, released vast amounts of radioactive carbon-14 into the air. A carbon-14 atom has two extra neutrons.
When grapes grow on the vine, they absorb carbon dioxide, which contains both stable carbon and traces of radioactive carbon-14 left over from bomb tests, from the air. As time goes by, carbon dioxide emissions from fossil fuel burning dilutes the amount of carbon-14 in the atmosphere.
The proportions of the different types of carbon pinpoint the wine's age. This method could be used to date other consumables, if we didn't have expiration dates. Link -via Arbroath