Burnt grain and crop cleaning residues: an archaeobotanical contribution to the understanding of 3rd–6th century AD longhouses in Jutland and Funen (Denmark)

Abstract

This paper uses the composition and spatial distribution of carbonised archaeobotanical material from postholes to identify and delineate agrarian and household activities within settlements. The paper presents the analyses of seven houses/farmsteads dating to the 3rd–6th century AD, which were excavated on four separate sites: Flensted, Skovby Nygård and Gedved Vest in east-central Jutland, and Odensevej on the island of Funen. To infer settlement activities from the distributions of carbonised plant macro remains, the paper defines the various stages of plant processing and carbonisation circumstances. It also discusses assumptions about plant processing sequences and the formation of charred plant assemblages that were made during the analysis. The results show that the distribution of charred plant macro-remains can assist in the identification and delineation of spaces with different functions. The presented cases identify the locations of dwelling spaces, spaces where processed crops were stored and/or used, and spaces where fine sieving of grain was performed. The results also show a similarity between the analysed houses, which suggests the existence of a regional tradition of ordering household space. These patterns also confirm assumptions about mid-1st millennium houses previously made on the basis of other archaeological evidence. IANSA 2020 ● XI/1 ● 47–62 Radoslaw Grabowski: Burnt grain and crop cleaning residues: an archaeobotanical contribution to the understanding of 3rd–6th century AD longhouses in Jutland and Funen (Denmark) 48 they are often assumed to have been used for agriculture or crafts and are commonly termed “economy buildings” (DK: økonomibygning) (Hedeager and Kristiansen, 1988, p.142; Hvass et al., 1988; Ethelberg, 2003, p.226; Jensen, 2003, p.214; Mikkelsen and Nørbach, 2003, p.23; Herschend, 2009, p.236). From the earlier Scandinavian Iron Age (c. 500 BC– AD 100) a significant number of houses with preserved floor layers, pavements and artefact spreads have been encountered over the last hundred years; especially in the west of the country where a combination of less intensive agriculture and aeolian movement of sand have acted as factors for excellent preservation. Through these finds, detailed inferences about the use of domestic space have been possible (see comprehensive summary in Webley, 2008). For the later Iron Age, the paucity of artefacts, preserved floor layers, and architectural traces indicative of function makes interpretation of the internal arrangement of late Iron Age houses more difficult, especially in the many cases where no hearths or animal stall walls are present. This has, over the years, led to attempts at using various natural scientific approaches, such as soil phosphate mapping and plant macrofossil analysis, to provide additional insights. The use of these methods is still at a stage of evaluation by the broader archaeological community. This makes the dissemination of promising examples important. 2. Aims and organisation of the paper The main aim of this paper is to illustrate the potential contribution that archaeobotanical analysis of carbonised plant macro remains can make to the understanding of late Iron Age longhouses. Furthermore, the paper aims to provide a broad outline of the key principles and assumptions that underpin analysis of charred macrofossil distributions in houses. This is done in the hope of making the approach more accessible to colleagues outside of archaeobotany, especially those who regularly excavate settlements and are responsible for the collection of samples. The aims are pursued in three steps. Firstly, in the theory section (Section 3), the formation, circulation and preservation of carbonised botanical material is explored. The focus lies on cereal crops and arable weeds since these categories of plant material make up the majority of all archaeobotanical finds from late Iron Age settlements (excluding charcoal). The method and material of the study are presented in Sections 4 and 5 respectively. In Section 6, the patterning in the botanical record from each case study is presented and interpreted within the framework established in Section 3. Lastly, in Section 7, the broader implications of the results for understanding 3rd–6th century habitation are discussed. Figure 1. Plan and hypothetical reconstruction drawing of a late Iron Age longhouse at Vorbasse in Jutland (after Hedeager and Kristiansen, 1988, p.139). IANSA 2020 ● XI/1 ● 47–62 Radoslaw Grabowski: Burnt grain and crop cleaning residues: an archaeobotanical contribution to the understanding of 3rd–6th century AD longhouses in Jutland and Funen (Denmark) 49 3. Theory: the formation, circulation and preservation of carbonised plant remains on settlements 3.1 The chaîne opératoire of plant processing Botanical material can become preserved by carbonisation if it is exposed to the right combination of heat (usually 250–500°C) and low-oxygen conditions (Miksicek, 1987). Once carbonised, such material is no longer biologically degradable but can still be damaged and fragmented through mechanical action. In archaeology, preserved plant remains are rarely studied as individual finds, but rather as assemblages sampled from natural or cultural deposits. While often used for understanding cultural phenomena such as the use of domestic space, and hence acting as (micro-) artefacts of human behaviour, botanical assemblages have some properties which make them different from other forms of material culture. Assemblages of charred plant remains are not manufactured in the same way as most artefacts but are instead assembled (sorted, mixed, accumulated) due to processes related to the procurement (harvest/gathering), sorting, cleaning, storage, preparation, consumption and discard of plant resources. Since these processes tend to follow a specific order they can be understood as botanical chaînes opératoire (operational sequences) of plant use (Hillman, 1984; Jones, 1984; Viklund, 1998). On Iron Age settlements in Scandinavia, cereals and weeds make up the majority of all carbonised plant macro remains (excluding charcoal). The operational sequences of these plant categories are therefore the most relevant for understanding the use of space. From historical sources in Scandinavia, and ethnographic documentation in regions where pre-industrial agriculture was still practiced in the recent past, we know that the processing of cereals usually required 30 or more separate steps (see summary example in Figure 2) (Erixon, 1956; Brøndegaard, 1978; Hillman, 1984; Jones, 1984). This degree of detail is, however, rarely traceable archaeologically, and practitioners of Scandinavian archaeobotany tend to work with simplified sequences such as: 1) harvest, 2) threshing, 3) coarse and fine cleaning, 4) storage, 5) consumption and 6) various forms of discard (e.g. Engelmark, 1989; Henriksen and Robinson, 1996; Viklund, 1998; Mikkelsen and Nørbach, 2003; Grabowski, 2013). In general terms, it can be said that three main changes will occur in the composition of cereal assemblages meant for consumption during processing. Firstly, the ratio of non-edible to edible parts of cereal plants will decrease as non-edible parts are separated from the grain. An example of this is the breaking of the ears with a threshing flail and removal of the straw, glumes and rachises by sieving, flinging and winnowing. Secondly, the ratio of weed seeds to grain will also decrease as weeds, which are unwanted in both food and seed, will be sorted away with different techniques. Because all sorting relies on size and/or weight, weeds with weights and shapes similar to those of grain will be the last to be removed. Thirdly, small and large cereal grains may be sorted into batches of different size (Hillman, 1981; 1984; Viklund, 1998; Stevens, 2003; Fuller et al., 2014). From historical records we know that grain was sorted into categories from the very best, known as prime grain, which was used for sowing, through mid-grain, which was used as food, to the smallest, the so called tail grain, which was regularly mixed with straw and chaff and given to animals, but could also be consumed by people in lean years (Erixon, 1956; Engelmark, 1989; Larsson, 2017). Ethno-archaeological middle-range studies such as the one by Jones (1990) provide real-life demonstrations of the changes in botanical assemblages that occur over the course of an operational sequence. Using ternary graphs, Jones has been able to show that assemblages from different processing stages have distinct ratios of grain to weeds to rachises (Figure 3a). Such modern data is useful for interpreting archaeobotanical assemblages, but as Jones rightly points out, we must be aware of possible differences in the handling of different crop species (her study concerned barley and naked wheat). Furthermore, the precise composition of botanical assemblages at specific points during processing may vary Figure 2. A schematic summary of historical (late 19th/early 20th century) hulled barley processing in Sweden (after Engelmark, 1989, p.183). IANSA 2020 ● XI/1 ● 47–62 Radoslaw Grabowski: Burnt grain and crop cleaning residues: an archaeobotanical contribution to the understanding of 3rd–6th century AD longhouses in Jutland and Funen (Denmark) 50 from one community to another, or even between individual farmers (Jones and Halstead, 1995) due to differences in agricultural habits and different concepts of what the desired product is supposed to be. For these reasons, some studies use a simplified categorisation of the botanical record into grain-rich, weed-rich and chaff-rich assemblages when comparing samples, features, houses and sites (Jones, 1985; Veen van der and Jones, 2006; Figure 3b). Because the activities which create differently-composed archaeobotanical assemblages tend to be performed in different parts of a settlement, the inference of the operational