How can archaeologists identify the production of ancient beer?
One of the most effective techniques is residue analysis. With this, archaeologists look for organic residues that are preserved in ancient vessels, such as ceramic pottery. Pottery is ubiquitous at many archaeological sites. Upon discovery, the vessels must be treated properly and washed correctly (or not at all) to ensure that the organic residues are not destroyed or contaminated. Contamination/destruction is a particular problem for vessels that were excavated many years ago because of the frequent use of acid washes and the subsequent, improper storage.
Ancient residues are not always found on the surface of the vessels, but they are collected from inside the pores of the vessel. Archaeologists drill into the pot, remove part of the surface, and collect a sample of the pot dust/residue mixture. Organic solvents are then added to the dust to dissolve the lipids (fats) and separate them from the ceramic materials. Next, a gas chromatograph is used to extract the lipids in gas form. This extract is subsequently placed in a mass spectrometer to identify diagnostic lipids.
The most common lipids that are identified include food products, wax, bitumen, pine, and other oils. Wine can be identified by the presence of tartaric acid and beer by calcium oxalate (beerstone). Recent studies have also been used on modern brewing equipment to identify isinglass, a fining agent, by measuring the hydroxyproline (Baxter, et al. 2007). Certain types of yeast can even be isolated, but many of the specific varieties cannot be differentiated. Interestingly, some colonies of bacteria have been found in ancient beer samples, suggesting a secondary or parallel lactic acid fermentation of the beer (Hornsey 2003). Who doesn’t love a good sour beer?
Residue analysis has returned to the news with the discovery of the “World’s Oldest Microbrewery” in Mijiaya, China (ca. 3500-2900 BCE). Using this technique, scientists determined the presence of barley, millet, and Job’s tears in a number of vessels, with other adjuncts such as snake gourd root, yam, and lily. Another early brewery was found at Godin Tepe (3400-3000 BCE) in the Zagros Mountains with the presence of calcium oxalate on the lip of a wide-mouthed jug. Patrick McGovern, the poster boy of beer archaeology, made this discovery and went on to collaborate with Dogfish Head Brewery for many modern interpretations of ancient beers that have been reconstructed with residue analysis.
Sources
Baxter, E.D., et al. 2007. “Analysis of Isinglass Residues in Beer.” J. Inst. Brew. 113(2): 130-134; Hornsey, I.S. 2003, A History of Beer and Brewing.
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Pottery from Godin Tepe. Source: © user: Siren-Com/Wikimedia Commons/CC-BY-SA-3.0
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