Experimental archaeological exploration of Meso-lithic techniques for hazelnut roasting

W. Lage

Archäologisches Landesmuseum Schleswig-Holstein, Schleswig

In the Duvensee Moor of Schleswig-Holstein, multiple Mesolithic sites with numerous shells from partially roasted hazelnuts in addition to non-local clay layers were discovered during the 1900’s. These finds were interpreted as the remains of a roasting facility. In this article the results of both short and long-term applied expe-rimental archaeology attempts at the reconstruction of these roasting stations will be reported.

The regular observation at these sites of charcoal layers below the clay strata, soot covering on the underside of a pair of clay plate fragments, as well as the signs of vitrification on the upper surface of the plates are taken as significant evidence for this analysis. Similarly, the structure of these features could be produced experimentally by placing a dried clay plate on wooden supports over a fire, with hazelnuts roasting in a bed of fine sand on top of the plaque. Hence, the const-ructions in the Duvensee Moor do not just provide an early sign of the separation of prepared foodstuffs from the fire. Rather, the employment of the clay and the observation of vitrification might point to an impetus towards the eventual manu-facture of ceramics.

Mesolithic, long-term experiment, hearth construction, ceramics

INTRODUCTION

The Mesolithic sites in the Duvensee Moor, Kreis Lauenburg, in southeast Schleswig - Holstein are on what was once a peninsula in the northwest part of the former Duvensee lake that dried out du-ring a fall in sea levels during the ele-venth century B.P. These locations fa-vored by hunter-gatherers represent, in

the opinion of the last locally active ar-chaeologist Klaus Bokelmann, predo-minantly hazelnut roasting places. Their function was essentially to preserve the nuts gathered there in the autumn from spoilage through roasting. A second ex-planation is the preparation of the hazel-nuts for their transformation into meal.

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RESEARCH PAPER

SCHRIFTEN DES NATURWISSENSCHAFTLICHEN VEREINS FÜR SCHLESWIG-HOLSTEIN

SUBMITTED 06-12-2009 ACCEPTED 23-12-2010 ONLINE 28-12-2010 © 2011 The Author

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The sites 1, 5, and 11 that are central to this article were located on the be-fore mentioned peninsula that at that time may have been cut off from the mainland and presented as an island to humans. The material remains from the residential area date altogether to the early Boreal.

As already presented (Lage 2004), the hearths exposed at the settlement sites were predominantly characterized by the presence of clay strata that were directly underlain by charcoal bea-ring layers. These observations were made by the first excavator at Duven-see, Gustav Schwantes, in 1924, ba-sed on his work at the later named Duvensee, “dwelling site 5” (after Bokel- mann 1971, profile 6). The ensuing excavation in 1946 at Duvensee, “dwel-ling site 1” by Hermann Schwabedissen confirmed these earlier results with a

base of charcoal overlain with a clay layer. Schwabedissen found a further clay layer covering a layer with char-coal (after Bokelmann 1971, profile 3).

The excavation of Duvensee, “dwelling site 11” led by Klaus Bokelmann from 1996 to 2001 also revealed four areas with clay concentrations, two of which proved suitable for further analysis as their stratigraphy was only negligibly disturbed (Bokelmann 2012).Of main concern are the hearths A and B that were not as originally sur-mised built on a layer of loam to pro-tect them from the bog, but rather on the few centimeter thick gyttja (he-arth A) as well as on an underlay of birch bark (hearth B). The hearth ha-zelnut roasting station from the 1923

Figure 1: Position of the Duvensee Moor with the most important sites (Bokelmann 1991, 78, Fig. 3).

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Figure 2: Duvensee, “dwelling site 5”. The profile of the hearth shows at least three clay layers, which are all underlain by charcoal-bearing layers. The charcoal layer which repre-sents the first fire is situated on top of a bark mat (after Bokelmann 1971, profile 6).

Figure 3: Duvensee, “dwelling site 1”. The charcoal-bearing layers are clearly positioned under the clay layers. The hearth was built on top of an area covered by numerous hazel-nut shells (after Bokelmann 1971, profile 3).

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excavation from Duvensee, “dwelling site 5” was also situated on a birch bark mat.

The immediate observations about the two hearths gained during the exca-vation are preserved as digital vocal recordings from which the two follo-wing quotations derive. For hearth A, the order of the relevant layers is as follows: “below the clay layer were thick chunks of charcoal. It appeared that the basal portion of the oldest roas-ting location was sunken to a point” (excavator K. Bokelmann 1999, first film, 45:45 min.).

The archaeologists commented about hearth B that, “in this portion of the site was located what was deemed the younger of the hazelnut roasting

locations that was built on a birch bark mat” (excavator K. Bokelmann 1999, first film, 38:36 min.). Two fragments from the base of the three clay layers lying on top of one another in hearth A showed a soot co-ating on their underside. In both cases the two palm-sized frag-ments lay directly on top of the under-lying charcoal pieces. While they all contained extensive soot on their un-dersides, and while these important cir-cumstances came to notice, it was pos-sible to surmise that the fragments lay loose on the ground where one could pick them up and use them. Normally the clay layers would be excavated from above as usual, so that the consistency of the underside could not be verified.

Figure 4: Duvensee, “dwelling site 11”, hearth B. White sand and products of the decom-position of the clay plate – silty material and sand which is naturally present in clay – are found underneath the plate remnants but also between the charcoal chunks. Finally, the “brown sand” accumulated on the charcoal layer (M: 10 cm; Profile seen from the south. Excavation K. Bokelmann 1998; graphic drawn from photo: W. Lage).

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FIRST INTERPRETATIONS OF HAZELNUT ROASTING

A first interpretation (Bokelmann 1981) proposed a sand casing completely sur- rounding the roasting hazelnuts on all side. A cone-shaped wood fire arranged on top provided the necessary heat. A further interpretation put forward, is that the coals from a previously lit fire were placed along with the hazelnuts in a similar sand casing that covered both coals and nuts on all sides (Bokel-mann u.a. 1985).Both interpretations were tested th-rough experiments on November 9th, 2002. The scientific expectations were not fulfilled:

During the course of carrying out the first experiments it was apparent that the heat arranged on the outside of the sand wall enclosing the nuts rea-ched only the outside hazelnuts, but the temperature was not enough to ro-ast the nuts lying in the inside of the pile. Furthermore, while the coloration of the nutshells was hidden from view, the roasting process could not be di-rectly observed, resulting in a dan-ger of overheating. Some nuts were

blackened and therefore made inedible. The second experiment failed because the embers enclosed in the sand with the hazelnuts were smothered and did not reach the required roasting tem-perature.

As a consequence of these experimen-tal archaeology attempts, the original interpretations from the excavator were discarded (Bokelmann 2012). Instead Klaus Bokelmann today favors a model based on the mongongo nut roasting process employed by the Bushmen. Therefore, the approach used by the Dobe !Kung was also replicated du-ring a joint experiment in 2002. A ten centimeter thick sand layer was hea-ted by a wood fire. Subsequently, the burning charcoal was positioned in a ring around the heated area. Then, a pit was excavated in the center of the ring and filled with hazelnuts and covered with hot sand. After approxi-mately 20 minutes time in the sandpit the nuts were roasted. Accordingly, this attempt could be considered suc-cessful, and in particular showed that a clay base was not required.

An important insight brought to light by the excavation was the red colo-ration produced on the surface of the clay layers. These red areas, which

are documented through drawings and which lay decomposing in the peat bog for 10,000 years, will be discus-sed below.

THE NEW HYPOTHESIS FOR HAZELNUT ROASTING

Since 2002, approximately a do-zen further experiments were con-ducted in addition to the three described above testing the obser-vations made during the excavations.

A new hypothesis for the reconstruc-tion of Mesolithic hazelnut roasting stations was developed based on the idea that the excavated clay layer was once a mobile clay plate. Over time

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Figure 5: The figure shows an air-dried clay plate, fired from below, with an overlying sand bed in which the hazelnuts are roasted. Dia-meter of the clay plate: 0.85 m, thickness of the plate at its center: 0.045 m, distance between ground level and underside of clay plate: 0.15 m, weight of the clay used to make the plate: 48 kg (photo: W. Lage).

the edge of the clay plate was so pro-foundly melded with the surrounding sediments, that the clay deposit was no longer recognizable as a mobile plate.

This hypothesis was also validated through experimentation. During the course of the experiment, the clay plate, with help of wood braces, was so po-sitioned that it was possible to light a fire underneath, which then roasted the hazelnuts lying in a sand bed on the clay plate (Lage 2004). Two such wood braces were recovered during the excavation on the edge of the clay concentration.

An additional potential wood brace lay in the area immediately adjacent to the shore. In contrast to the hearth wood remains that were redeposited in the water which mostly had char-ring one side, the branch segments used to hold up the plate showed a meshed coalification.

Methods

After the functional capacity of the above outlined attempt was con-firmed, a 5-year long-term ex-periment was used to investi- gate how closely the decomposition pro-ducts of the roasting site matched those of the original archaeological feature. Following completion of the hazel-nut roasting experiment, the end pro-ducts were left for five years. The goal therein was to answer two questions: 1. What happens to the clay plate, when left exposed and unprotec-ted from natural erosion forces?

2. Would materials found during the excavation under the clay concentra-tion such as charcoal, white burned sand as well as brown sand also be found after the experimental hearth was left for just five years?

The acquisition of an infrared tem-perature measuring instrument from the local institute made it possible to draw conclusions about the dispersal of heat energy from the fire, which ge-nerated, among other things, the vi-trified appearance on the clay plate. The clay slab was, during the attempt, covered with sand that served as a matrix for the nuts.

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RESULTS

As already described in detail (Lage 2004), the clay plate broke chiefly on the boundaries bet-ween vitrif ied and non-vitrif ied regions on the plate. Whereas the non-vitrified parts were predominantly located near the wood braces, the vi-trified areas were naturally located in the central portion of the clay plate. The plate broke after approximately three months. This event was possibly expedited by rain or animal activities. Following the breaking of the plate a portion of the burnt sand trickled th-rough the gaps to mix in with the ch-arcoal lying beneath.

During the excavation of the long-term experiment, with special thanks to ar-chaeologists Daniela Holst and Sonja Grimm from the Römisch-Germani-sches Zentralmuseum Mainz for their participation, it was observed that the burned sand that lay beneath the plate fragments in places had become yel-low-brown colored. A possible expla-nation for this coloration is the fact that rain caused crumbling in the split areas of the plate causing it to further dis-solve with silty clay components was-hed into the deeper layers. This would cause the yellow-brown discoloration of the previously white burnt sands.To summarize, following the comple-tion of the experiment it was possible to confirm already after five years that the materials under the clay plate frag-ments were the same as those dis-covered in the original archaeologi-cal feature.

In order to be able to follow the pro-cess and the intensity of the heat pro-duced in the fire under the clay plate,

on June 19th 2011 an infrared tempe-rature measuring device with attached sensor was employed. The beam of the infrared laser was directed at the sand bed resting on the surface of the clay plate. For parallel measurements a sensor that registered the temperature development between the surface of the clay plate and the overlying burnt sand was used.After 3.5 hours of firing, a clay plate with overlying sand bed reached a tem-perature of 465°C and 135°C on the surface of the sand. Inside the sand bed a temperature of 297°C has been assessed.

The observed downward temperature gradient between the upper surface of the clay plate and the sand bed resulted because the sand impedes the imme-diate continuation of the heat energy. The energy encounters a heat buil-dup between the differently conduc-tive materials, which is the cause of

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Figure 6: First phase of the long-term expe-riment. The clay plate broke after approxi-mately three months, the rim of the plate is beginning to disintegrate. The charcoal is covered and hence protected, while the sup-porting wood braces are partly uncovered. Most of the roasting sand is still lying on the plate, but part of it is washed away and has run through the cracks (photo: W. Lage).

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DISCUSSION

The hypothesis whereby all activities concerning hazelnut roasting occur-red on a clay plate, see the charcoal concentration found under the clay floor as belonging to a preceding ac-tivity with no connection to the roas-ting process (Bokelmann 2012). This “clay floor theory” overlooks the fact that only through a fire as represen-ted by the charcoal could the changes to the overlying clay occur, such as:

the burning of not just the upper sur-face of the clay plate but also the in-side of the plate.

The heat buildup is induced by the grainy structure of the sand (personal

communication Roland Aniol, physicist at the Archäologisches Landesmuseum Schleswig-Holstein). This allows only an impaired convection, works as in-sulation, and results in the observed phenomenon.

1. soot formation on the undersides of two clay plates, and

2. the red coloration of the upper sur-face of the clay plates.

If a clay floor were created by placing clay on the supposedly already pre-sent charcoal resulting from an earlier activity, it would fill in the irregularities and hollows and incorporate the fire

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Figure 7: Duvensee, “dwelling site 13”. The clay plate remnants which are contained in the white roasting sand are underlain by a layer containing charcoal. In a profile drawn half a meter further east, the clay band has started decomposing into a brown sand lens. Con-sequently, the base of the hearth consisting of sphagnum peat is mostly covered with brown-yellow but also with white sand (excavation K. Bokelmann 1982, profile U; East: 5.50 m; graphic drawn from profile drawing U: W. Lage).

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residues. Pertinent to consider here are the observations from the 27th of June 2011 experiment. The neces-sary surface pressure to create the clay was achieved through tapping of the clay which resulted in the penet-ration of the plastic mass into the in-tervening spaces of its resting place. But, the “clay floor theory” cannot be

upheld as neither the underside of the two clay fragments coated with soot from hearth A, nor the vertically ex-posed visible clay bands contained charcoal or other inclusions but were rather smooth. Indeed the two upper clay layers (plates) from hearth A had settled into a bell shape over the al-ready accumulated basal roasting area. The curvature resulted from the long

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Figure 8: Ethnographic parallels to the methods of food preparation employed by Mesolit-hic peoples are to be found in the Scandinavian Sami culture (Tuomi-Nikula 2001). Tem-porary exhibition at the Archaeological State Museum of the Foundation Schleswig-Hol-steinische Landesmuseen Schloss Gottorf, Schleswig. Instead of hazelnut meal and a clay plate, the reindeer herders used bark meal for baking flat bread on a hot stone heated from below. This method of cooking has also been proposed for the late paleolithic (Stapert 1982).

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The author is very thankful to Susan Harris, Santa Barbara, and to Mara-Julia Weber, Schleswig, for translating this contribution from German into English.

I am very grateful to Ulrich Schmölcke (ZBSA, Schloss Gottorf, Schleswig) who proofread the manu-script with his accustomed care and efficiency.

term effect of the load of the develo-ping bog. This had otherwise no ef-fect on the composition of the under-sides of the level clay plates.

As explained in the methods discourse, burning of the clay plate comparable to the original archaeological finds is only possible with firing from under-neath. By contrast a clay floor covered with a six centimeter thick sand layer achieved only a maximum tempera-ture between 180 to 200 °C after two hours with a burning wood fire. This left behind a blackening but no signs of vitrification.

Duvensee, “dwelling site 13“, dated to the late Boreal, exhibits a hearth with a diameter of 1.3 meters and is made of an up to 12 centimeter thick “roun-ded fill of yellow sands“ (Bokelmann u.a. 1985; Holst 2007). However, the profile documentation from the area of the hearth shows a more differentia-ted picture. Here we see a clay layer characterized by fissures underlain by a layer containing charcoal (see Fi-gure 7). The white sand situated on the clay layer had, in some cases, flo-wed between the pieces of charcoal.Hence, there is a further hazelnut ro-asting site example (Duvensee, dwel-ling site 13) to combine with those from

Duvensee, dwelling sites 1, 5, 11 that exhibits a clay layer underlain by ch-arcoal, and that supports the model for an air-dried clay plate, fired from below, and with a sand bed on top in which the nuts were roasted.Finally, a further consideration is that charcoal, which is easily washed and blown away, survived until present times. If the charcoal, as postulated by the “clay floor theory”, was depo-sited on top of the clay layer, the au-tumn storms on the edge of the sea as well as the proven flooding of the area would have shown their erosio-nal effects. Only the tenacious mass of the collapsed clay plate protected the charcoal from otherwise highly li-kely erosion.

The following ethnographic analogy to the proposed model suggests that this roasting knowledge was passed down over long periods of time and survi-ved until today. In Egypt, peanuts are still roasted in a sand or salt bed on top of a clay plate. This simple hearth structure is heated from a wood fire below the clay plate. This method is supposedly favored by the Egyptians because of the pleasant flavor of nuts treated in this manner (personal com-munication Klaus Bokelmann).

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REFERENCES

Bokelmann, K. (1971): Duvensee, ein Wohnplatz des Mesolithikums in Schleswig-Holstein und die Duvenseegruppe, Offa 28, 1971, 5–26.

Bokelmann, K. (1981): Eine neue borealzeitliche Fundstelle in Schleswig-Holstein. Kölner Jahrb. 15 (= Festschrift H. Schwabedissen), 1975–1977 (1981), 181–188.

Bokelmann, K., Averdiek, F.-R. , Willkomm, H. (1985): Duvensee, Wohnplatz 13. Offa 42, 1985, 13–33.

Bokelmann, K. (1991): Duvensee, Wohnplatz 9. Ein präborealer Lagerplatz in Schleswig-Hol-stein. Offa 48, 1991, 75–114.

Bokelmann, K. (2012): Spade paddling on a Me-solithic lake – Remarks on Preboreal and Bore-al sites from Duvensee (Northern Germany). In: M. J. L. Th. Niekus, R. N. E. Barton, M. Street & Th. Terberger (Eds.), A mind set on flint. Studies

in honour of Dick Stapert. Groningen Archaeo-logical Studies 16. Barkhuis: Groningen.

Holst, D. (2007): Subsistenz und Landschafts-nutzung im Frühmesolithikum: Nussröstplätze am Duvensee. Dissertation Universität Mainz, 2007, 129–141.

Lage, W. (2004): Zur Interpretation der Lehmstra-ten in den Feuerstellen des Duvenseer Moores – Lehmplatten als Gar- und Röstvorrichtungen während des Mesolithikums in Schleswig-Hol-stein. Archäologisches Korrespondenzblatt 34, 2004, 3, 293–302.

Stapert, D. (1982): A site of the Hamburg tradition with a constructed hearth near Oldeholtwolde (Province of Friesland, the Netherlands); first report. Palaeohistoria 24, 1982, 53–89.

Tuomi-Nikula, O. (2001): Sápmi. Das Land der Fischer, Jäger und Rentierzüchter.

Wolfgang Lage (jahawo@t-online.de)Archäologisches Landesmuseum Schleswig-HolsteinSchloss Gottorf24837 Schleswig

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