Revealing Lipid Analysis at Anglo-Saxon sites in Suffolk

Recent work by Dr Julie Dunne on Bronze Age burnt mounds has found lipids surviving in the fissures of heat-altered flint. Lipids are, in Dunne’s words, ‘the fats, waxes and resins of the natural world (and) are the most frequently recovered compounds from archaeological contexts’. Dunne’s work on Bronze Age lipids has advanced the study of the function of Burnt Mounds. Encouraged by this success, at the beginning of lockdown the post-ex team at Suffolk submitted further samples to Dr Dunne at Bristol University, although in this case it was Anglo-Saxon activity we were hoping to interpret.

One of the burnt pits from Eye after the flints have been removed and showing the base layer of charcoal and in situ burning
One of the burnt pits from Eye after the flints have been removed and showing the base layer of charcoal and in situ burning

A common but enigmatic feature of many Anglo-Saxon settlements in Eastern England are rectangular pits, filled with fire-cracked flint and charcoal, with evidence of in situ burning. Most fall within a size range of 1.5m–2.5m by 0.7m–1.5m; their depth is more variable and site specific. These are usually undated by finds; the first excavated examples were assumed to have been prehistoric and were therefore not included in the description of the Anglo-Saxon phases. However, over the last 15 years the link with the Anglo-Saxons has been confirmed by minimal finds dating, radiocarbon dating and spatial association. But what are they for? The pits appear typically to have had a single use and they occur too infrequently to be representative of everyday activity. Evidence from one such pit at Eye in Suffolk suggested that the flints were placed on a lattice of wood over a fire in the base of the pit. Presumably as the fire burnt the flints would collapse into the pit, shutting out the oxygen and smothering the fire, leaving a bed of ‘hot rocks’. But for what? Cooking, perhaps for an occasional feast? An industrial process? We now have an answer.

Members of the team at Eye lift carbonised wood, part of the lattice on which the flints were placed
Members of the team at Eye lift carbonised wood, part of the lattice on which the flints were placed
One of the pits from Kentford half excavated and with the pile of heat-altered flint removed from it in the foreground
One of the pits from Kentford half excavated and with the pile of heat-altered flint removed from it in the foreground

Lipid analysis was undertaken on flint samples from two Early Anglo-Saxon settlements in Suffolk, at Eye, in the north of the county, and Kentford, in the west. There are seventeen such pits at Eye and seven at Kentford. Three of the pits from Eye and one from Kentford produced positive results, with lipid profiles comprising ‘the free fatty acids, palmitic (C16) and stearic (C18), typical of a degraded animal fat’ (Dunne 2020) (see chart below). Once plotted the result shows that these profiles fit within the range of the ‘ruminant adipose ellipse suggesting the lipids originate from animal products produced by the cooking of ruminants, such as cattle, sheep or goat’ (Dunne 2020). The similarity in evidence from both sites suggests a common purpose and Dunne suggests that it is likely that this reflects the roasting of large joints or whole animals, but most notably not pigs (nor horses, although butchered horse bone was recovered from Eye). These results are ‘hot off the press’ and we now need to consider how we interpret them in the light of the settlement evidence from the two sites; we can say that this represents an occasional, and therefore perhaps special, cooking event that sometimes took place at Anglo-Saxon settlements in East Anglia.

We also need to research old excavation reports to find ‘lost’ examples. One of the great things about lipids from the perspective of an archaeological researcher is that they are resistant to decay, so if a sample of the heat-altered, fissured, flint has been kept the possibility of retrospectively testing for lipids exists.

Jo Caruth

Graph showing: a. δ13C values for the C16:0 and C18:0 fatty acids for archaeological fats extracted from three samples of burnt stone from pits at excavations at Hartismere High School, Eye (blue) and one sample from Kentford Lodge, Kentford (red)

Ref. Dunne, J., Gillard, T., and Evershed R, P. 2020. Organic residue analysis of burnt stone from Hartismere High School, Eye, Suffolk: Report. and Organic residue analysis of burnt stone from Kentford Lodge, Kentford, Suffolk: Report. Unpublished, Bristol University

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