Over The Horizon

Pine in Wine

Ancient wine provided an unusual source of inspiration for Fulbright scholar Douglas Stewart. While an undergraduate in the United States, he had the opportunity to study an Etruscan artifact whose contents, a class of compounds called diterpenoids, ultimately led him to New Zealand, where he is studying their chemistry in native trees.

The Etruscans were a somewhat mysterious civilization that thrived on the Italian peninsula in pre-Roman times. Only fragments of their largely-undeciphered language remain, so knowledge about Etruria stems from analysis of archaeological artifacts. Many of these artifacts come from Etruscan tombs. Like the Egyptians, the Etruscans buried everyday objects to be enjoyed in the afterlife.

One such tomb, dated to the 5th century BC was excavated in the late 1920s at the Etruscan funerary complex at Spina, Italy, on the Adriatic Sea. Among the objects found was a highly decorated bronze pot, called a situla. Adhering to the bottom was a clump of organic material. At that time, there were no analytical methods that could reliably determine the composition of a complex organic mixture.

One of the most powerful methods developed since then have been the combination of gas chromatography and mass spectroscopy (GC/MS). A GC/MS instrument separates nanograms (10^-9 grams) of a complex mixture into individual components and then produces a mass spectrum of each component. From the mass spectrum, the molecular weight and structure of each component can be determined, as can a rough estimate of the quantity of each component.

The bit of organic matter at the bottom of the situla was most likely a pine resin, pitch or tar. Pitches and tars, produced by heating pine resins, were a commodity in ancient times and used on ships, barrels and other containers as a water-proofing agent.

Absolute identification depended upon the GC/MS data. The instrument separated nearly 50 components that comprised the sample. By studying the ratios of certain molecular structures in the sample, confirmation was obtained that the sample did originate from a pine tree.

Had the sample been heated in the past, large numbers of degradation products -- molecules formed by heating -- would have been evident. None were spotted. This and other evidence indicated that the sample was a pine resin.

What was a piece of pine resin doing at the bottom of a beautifully decorated bronze pot? Apparently the vessel had been used to hold wine, and pine resin was added to impart a flavor to the wine. Resinated wine, called retsina, is still produced in Greece today, as it has been since antiquity.

Although the Etruscans may have independently developed a taste for retsina, it is more likely that they acquired it from the Greeks, who had a trading center at Spina.

Chemistry has thus allowed us to glimpse an exchange of ideas 2,500 years ago.