Lee Eales (1), Duncan Cameron (1), Robert Falconer (1); (1) University of Sheffield, Sheffield, U.K.
Technical Session 18: Evolution of Brewing
Tuesday, August 16 • 3:30–5:15 p.m.
Plaza Building, Concourse Level, Governor’s Square 15
Understanding the drivers of changes in consumer preferences is complex; this is especially the case when those changes occurred nearly 1,000 years ago. The Medieval Period (1066-1530s) was a time of unprecedented fluctuations in population, technological advancement and social organization. Beer and beer production was a major contributing factor to population growth, as beer is largely free of human pathogens. At the start of the Middle Ages, beers were flavored with a mixture of herbs called gruit. By the end of the Middle Ages, gruit had been replaced by hops; however, when this change occurred is a matter of considerable debate among historians. With the modern analytical techniques at our disposal, it is now possible to tease out the answers to some of these questions by understanding the chemistry of beers in a historical context. Here, we present a novel method for the targeted analytical fingerprinting of chemical compounds for both hopped and un-hopped medieval beers found on and in the fabric of medieval ceramics. Ceramics from the Middle Ages were not internally glazed, thus the contents of the ceramics were in direct contact with the surface of the clays from which the ceramics were made. Clay minerals are usually negatively charged and, thus, have the capacity to act as ionic exchange surfaces, immobilizing positively charged ions. The flavor-giving alpha- and beta-acids and flavonoids found in beers are aromatic, containing cyclic carbon structures such as benzene and toluene rings. As a result of delocalization of electrons in aromatic compounds, they are predisposed to interact with charged surfaces and, thus, should be immobilized indefinitely by unglazed ceramics, as well as being protected from the active site of any enzymes capable of degrading them. As a result, these compounds are sorbed to the ceramic surface and subsequently can be analyzed by matrix assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSi). We have optimized MALDI-MSi for use on thin sections of medieval ceramics (600-800 µm) that have a well-established provenance for beer consumption and beer production taken from dated sites across the Medieval Period. Resultant mass spectral fingerprints obtained from residues on medieval pots were analyzed using dimensional reduction approaches (PCA and O2PLS-DA) allowing us to resolve the principal differences in the chemistry of the residues, the identity of those compounds and their biological origin (plants to the genus level). For method validation purposes, mass spectra were also obtained from contemporary analogue pots that had been treated with hopped and un-hopped beers. Combining our novel analytical chemistry approaches with both archaeology and written sources allows us to understand the temporal dynamics of changes in brewing ingredients over the course of the Middle Ages. This understanding permits the development of authentic brews using specific ingredients to the same technological standards in order to produce beers with aromatic and flavor profiles accurate for the historical period.
Lee Eales received a B.A. degree in classical archaeology from the University of Sheffield. He began a career as a commercial field archaeologist with Trent and Peak archaeological unit. After gaining experience with a number of commercial units both in the United Kingdom and Europe he took up a post as a supervisor to undergraduate students in the Archaeology Degree program at Sheffield, specializing in medieval archaeology. In June 2014 he took up a position as a postgraduate research assistant in analytical chemistry, also at the University of Sheffield, specializing in chemical residue analysis of medieval pottery. In particular he uses matrix assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSi) to profile the residue of organic materials captured both on and in the fabric of ceramics dating to the medieval period. He is currently a Ph.D. candidate on a project titled “The Sensory Archaeology of Medieval Brewing, Its Ingredients and Technology.”