Mashes to Mashes, Crust to Crust. Presenting a novel microstructural marker for malting in the archaeological record

Abstract

The detection of direct archaeological remains of alcoholic beverages and their production is still a challenge to archaeological science, as most of the markers known up to now are either not durable or diagnostic enough to be used as secure proof. The current study addresses this question by experimental work reproducing the malting processes and subsequent charring of the resulting products under laboratory conditions in order to simulate their preservation (by charring) in archaeological contexts and to explore the preservation of microstructural alterations of the cereal grains. The experimentally germinated and charred grains showed clearly degraded (thinned) aleurone cell walls. The histological alterations of the cereal grains were observed and quantified using reflected light and scanning electron microscopy and supported using morphometric and statistical analyses. In order to verify the experimental observations of histological alterations, amorphous charred objects (ACO) containing cereal remains originating from five archaeological sites dating to the 4th millennium BCE were considered: two sites were archaeologically recognisable brewing installations from Predynastic Egypt, while the three broadly contemporary central European lakeshore settlements lack specific contexts for their cereal-based food remains. The aleurone cell wall thinning known from food technological research and observed in our own experimental material was indeed also recorded in the archaeological finds. The Egyptian materials derive from beer production with certainty, supported by ample contextual and artefactual data. The Neolithic lakeshore settlement finds currently represent the oldest traces of malting in central Europe, while a bowl-shaped bread-like object from Hornstaad-Hörnle possibly even points towards early beer production in central Europe. One major further implication of our study is that the cell wall breakdown in the grain's aleurone layer can be used as a general marker for malting processes with relevance to a wide range of charred archaeological finds of cereal products.

Fig 1. Simplified chaîne opératoire of brewing actions together with their associated processes and traces in the archaeological record.

The diagram is based on historical and ethnographic records as well as on knowledge of modern brewing technology [, , , –40]. Only processes required for the formation of alcohol are described. Blue background: “core” actions and processes, grey background: optional actions and processes which are, for example, characteristic of modern beer making [19, 41]. Saccharification takes place in numerous stages of beer making, which is additionally illustrated by red arrows. Figure: University of Hohenheim / M. Berihuete Azorín; Office for Urbanism Zürich / N. Bleicher; ÖAW-ÖAI / A. G. Heiss; TUM-Weihenstephan / M. Zarnkow.

Fig 2. Embryo end of a bread wheat (Triticum aestivum) grain showing massive degradation of the endosperm.

a, b) unmalted grain, and c, d) after six days of sprouting. SE… starchy endosperm, Sc… scutellum. Fluorescence (CLSM) colours: yellow = cell walls, red = proteins, green = starch. Image: TUM-Weihenstephan / J. Helbing.

Fig 3. Bread wheat (Triticum aestivum) grain after six days of sprouting.

SE… starchy endosperm, A… aleurone. T… transverse cells. Fluorescence (CLSM) colours: yellow = cell walls, red = proteins, green = starch. Image: TUM-Weihenstephan / J. Helbing.

Fig 4. Archaeological barley (Hordeum vulgare) aleurone with regular wall thickness.

Fragment of a charred cereal product from the La Tène C period (c. 250–150 BCE) site of Haselbach, Lower Austria (find no. 252, SE 16–03 = SE 16–19). Top: light micrograph, bottom: SEM image. SE… starchy endosperm (fused remains), A1–A3… aleurone layers. Image: ÖAW-ÖAI / A. G. Heiss.

Fig 5. Experimentally charred hulled barley (Hordeum vulgare) grain after 1 day of malting.

Gl… glume, A1–A3… aleurone layers, SE… starchy endosperm (fused remains). Image: University of Hohenheim / M. Berihuete Azorín.

Fig 6. Experimentally charred hulled barley (Hordeum vulgare) grain after 5 days of malting.

Gl… glume, A1–A3… aleurone layers, SE… starchy endosperm (fused remains). Image: University of Hohenheim / M. Berihuete Azorín.

Fig 7. Site locations of the archaeological case studies.

Top: central European sites, bottom: Egyptian sites. Map: ÖAW-ÖAI / C. Kurtze, A. G. Heiss.

Fig 8. The partially charred cereal product from Hierakonpolis.

Find no. HK 11C. Top: light micrograph, bottom: SEM image. The material has been previously identified as emmer (Triticum dicoccum) based on caryopsis macroremains [148] in the food crust. Image: Helwan University, Cairo / E. A. E. Attia.

Fig 9. The charred emmer (Triticum dicoccum) product from Tell el-Farkha.

Feature 192/201 (vat contents). Top: light micrograph (red square: location of SEM subsample), bottom: SEM image. A… three patches of single-layered aleurone, SE … starchy endosperm (fused remains), N?… nucellus tissue. Image: Naturalis Biodiversity Center, Leiden / L. Kubiak-Martens.

Fig 10. The bowl-shaped charred cereal product (“brei mit napfförmiger oberfläche”) from Hornstaad—Hörnle IA.

Find no. Ho 45/43-28. Top: light micrograph (red square: location of SEM subsample), bottom: SEM images. Left: patch of regularly arranged aleurone cells (A) with a conspicuous intercellular space (*) in between. L… longitudinal cells, right: fracture through the outer caryopsis layers, the multiple aleurone layers (A1 –A3) identify the material as cultivated barley (Hordeum vulgare) as do the thin-walled transverse cells (T). SE… starchy endosperm (fused remains), N? … probably nucellus tissue, L?… probably longitudinal cells, E… epidermis (abraded).. Images: ÖAW-ÖAI / N. Gail (light micrograph), A. G. Heiss (SEM). See also S1 Model.

Fig 11. Charred cereal product (“feiner brei”) from Sipplingen—Osthafen.

Find no. Si10 538/127-1054. Top: light micrograph (red square: location of SEM subsample), bottom: SEM image, fracture through the outer caryopsis layers. The multiple aleurone layers (A1–A3) identify the material as cultivated barley (Hordeum vulgare). SE… starchy endosperm (fused remains), T… transverse cells. Images: ÖAW-ÖAI / N. Gail (light micrograph), die Angewandte / R. Erlach (SEM). See also S2 Model.

Fig 12. Charred cereal product with large chunks of grains (“grober getreidebrei”) from Sipplingen—Osthafen.

Find no. Si10 538/128-1030. Top: light micrograph (red square: location of SEM subsample), bottom: SEM image, fracture through the outer caryopsis layers. The multiple aleurone layers (A1–A3) identify the material as cultivated barley (Hordeum vulgare). N… nucellus tissue, T… transverse cells. Images: ÖAW-ÖAI / N. Gail (light micrograph), die Angewandte / R. Erlach (SEM).

Fig 13. Charred cereal product from Zürich—Parkhaus Opéra.

Find no. ZHOPE 12162.1A / AOV 85. Top: light micrograph, bottom: SEM image, fracture through the outer caryopsis layers. The multiple aleurone layers (A1–A2) identify the material as cultivated barley (Hordeum vulgare) and show conspicuous intercellular spaces (*). SE… starchy endosperm (fused remains), N… nucellus tissue. Images: UNIBAS-IPNA / F. Antolín.

Fig 14. Charred cereal product from Zürich—Parkhaus Opéra.

Find no. ZHOPE 6949.1. Top: light micrograph, bottom: SEM image, planar view of the aleurone layer. The presence of a single vs. multiple layers (A1? A2?) of aleurone is not clearly visible, therefore not allowing for precise identification of the material (cf. Hordeum vulgare). Images: ÖAW-ÖAI / A. G. Heiss (light micrograph), univie-VIAS / M. Mehofer & A. G. Heiss (SEM).

Fig 15. Example of data acquisition.

Measuring aleurone cell walls (double cell wall thickness) in experimentally charred barley (Hordeum vulgare) malt. Image: ÖAW-ÖAI / Andreas G. Heiss.

Fig 16. Aleurone double cell wall thicknesses in μm, observed in experimentally charred barley malt, compared to the archaeological finds of charred cereal preparations included in this study.

For descriptive statistics of the raw data see S3 Table, for normality tests see S4 Table, for post hoc tests see Table 1. Figure: ÖAW-ÖAI / A. G. Heiss.

Fig 17. Surface features (top) and cross section (bottom) of the bowl-shaped charred cereal product from Hornstaad—Hörnle IA.

The distinct cracked surface (craquelé [57]) pattern as well as the particle size sorting in the material are interpreted as resulting from a liquid state of the material prior to charring. Image: ÖAW-ÖAI / A. G. Heiss.

Fig 18. Model for the formation of the bowl-shaped bread-like object from Hornstaad-Hörnle.

1) cooking pot in regular use, surrounded by heated stones. During either a cooking accident, or in the catastrophic fire, 2) the heat causes the pot’s liquid content to boil, to dry out and to char progressively from the outside inwards until 3) only the final remains of the liquid are left in the centre. 4) All liquid is now dried out, and the outermost parts of the mass possibly even begin to burn to ashes (hatched areas). 5) The bowl-shaped innermost part of the charred mass breaks loose as soon as the pot falls over or is destroyed, or intentionally emptied and cleaned. Image: RPS-BWL / H. Schlichtherle. Modifications: ÖAW-ÖAI / A. G. Heiss.