British

Ancient hunter-gatherers did a lot of hunting, but not, in our imaginations at least, much gathering. Yet plant foods have always been essential to nutrition. Karen Hardy is developing new techniques that could open up a lost world of food and eating in Britain.

What we eat is a topic of perennial interest, as the popularity of celebrity chefs on TV demonstrates. No less interesting is the reconstruction of ancient diet, a better knowledge of which directly informs many aspects of our understanding of the past.

Ethnographic evidence from around the world demonstrates that virtually every known human group made extensive use of plants in their diet. This is unsurprising as we need plants to live, and not only for their minerals and vitamins. Humans need carbohydrates, of which starch – a macronutrient – is an important source. It is largely concentrated within storage organs of certain plants, such as roots, tubers, corms, rhizomes, nuts, grains and seeds. Most cereal starch is located in the endosperm, the central and largest part of the grain, whilst starch is the main component of tuberous root crops such as potatoes.

Today our starch comes from food such as bread, pasta, rice and potatoes; starch-based foods now constitute 50–70% of the energy intake of most humans. In pre-agricultural times, carbohydrates would have come from the many edible starchy roots and tubers that exist virtually everywhere (well over 60 different species in the UK alone), seeds and even inner bark: some trees store starch there, and it is known to have been exploited as food.

The small number of people who did not have access to a regular supply of high energy carbohydrates, such as in the high Arctic, replaced these with fats. This had some negative physical consequences, so fats are unlikely to have been used as a substitute where carbohydrates were accessible.

Despite all this, when we think of early diets, especially pre-agricultural ones, we focus on meat and seafood, largely ignoring plant foods except hazelnuts. Yet archaeobotanists have found extensive edible plant remains from numerous mesolithic sites, particularly from around the Baltic.

In Britain and Ireland, many of the edible roots and tubers are at their starchiest during the winter months, as they store their energy before the growing season begins. Two examples of very common plants that have highly starchy and edible roots are reedmace or bulrush (Typha latifolia) and pignut (Conopodium majus). They must have represented a huge resource for all pre-modern people, particularly as they are best eaten in winter when other food sources may have been more difficult to obtain. Their remains are amongst the many tuberous plants found at mesolithic sites in northern Europe. Even today, people still remember collecting pignuts as children in the mid 20th century; these roots are a major source of starch, and delicious roasted.

Stable isotope analysis of skeletal remains can determine the ratio of land to marine foods consumed. But with acidic soils destroying organic material on many archaeological sites in Britain, the problem is, how can we demonstrate and investigate food use from the potentially far more informative source of plant remains?

Starches and phytoliths

New analyses of microscopic starch granules and phytoliths from a range of archaeological samples from northern Britain and elsewhere have recently produced some fascinating results that offer a way forward to access direct information on ancient diet and material culture. Starch granules and phytoliths have been found adhering to the edges of flaked stone tools; as accumulations in the pores of the coarse granular structure of stones used for grinding and inside pots; in sediment; and in dental calculus.

Phytoliths are tiny silica bodies which form in growing plants. They survive the death of plants, and can be extracted from archaeological and soil samples. Phytolith shapes are frequently species specific. They have been used to identify plant types extensively in archaeology, particularly in the Near East and in America – but have been little used until now in northern Britain. Phytoliths can offer insights into local ancient environments, as well as the uses people make of them.

Starch is the major carbohydrate and energy reserve in seeds and plant tubers where it is usually found as granules. These granules are biodegradable and susceptible to enzyme attack; how starch survives on archaeological sites is still not completely clear, and is the subject of an international collaboration between myself and the Faculty of Agriculture, Food Science and Natural Resources, University of Sydney. It is however semi-crystalline and can apparently survive for long periods of time in a stable environment.

Most people have dental plaque biofilms on and around their teeth. Dental calculus, which occurs when these accumulate and mineralise, is associated with chronically poor oral hygiene and is very common in skeletons from all periods in the past. When the calculus is decalcified, microfossils of ancient food are left. These can be mounted on microscope slides, observed and often identified to plant genus in the case of starches, and species in the case of phytoliths.

Starches currently appear to be the most common macrofossil found in dental calculus. Assuming that things in the mouth are likely to have been consumed (though there are exceptions, such as chewing inner bark as part of string preparation), phytoliths and starch granules found trapped inside dental calculus represent a direct link to the consumption of starchy food by humans or animals.

I have found starches in dental calculus from iron age samples of both human and animal teeth from Kaman Kalehoyuk in Anatolia, from Roman and modern human teeth, and from modern chimpanzee teeth. Indeed, starches have been found in virtually every sample of dental calculus examined – including these cases from Britain.

Star Carr in Yorkshire is one of the most important mesolithic sites in Europe (see feature, Sep/Oct 2007). Recent pilot studies by Paul Crofts as part of his masters dissertation at the University of York, to explore the presence of starches here from material extracted from stone tools, have been successful.

High Pasture Cave is a late bronze age/early iron age site on the Isle of Skye (see On the web, Sep/Oct 2005). I took a series of samples through a large burnt mound beside the cave entrance, to determine whether starch granules and phytoliths were present, and to evaluate their potential as tools for dietary and palaeoenvironmental reconstruction in a northerly, wet environment. In the event, I found both starch and phytoliths. While the presence of the latter throughout the sequence is exciting but less surprising, the presence of starch granules in a number of the contexts was unexpected.

In the case of High Pasture Cave, starch occurred in several burnt layers and in charred residues extracted from pottery. Burning starch at high temperatures may alter its structure, and this may enable it to survive in conditions that otherwise would see it degraded within a few days in an unprotected environment. The small size and angular nature of most of the starch granules from High Pasture suggest that the starches came from a tightly packed environment such as the endosperm of a seed, rather than from a tuber.

St Ninian's is a Norse settlement in Shetland. Samples of dental calculus from here contained a wide range of material, including a pollen possibly of a Cupressaceae (conifer), in addition to starches.

Tarbat is a Pictish monastery site at Portmahomack in the Moray Firth. Here a medieval cemetery is being excavated by the University of York under the direction of Martin Carver, and numerous skeletons have been recovered. I extracted small samples of dental calculus from several Tarbat skeletons, and found numerous starch granules. The photo in the centre of page 26 demonstrates unequivocally that the person was eating a cereal, probably barley. While this in itself is unsurprising given the context, it represents an exciting new way to make a direct link between a foodstuff and an historical individual.

Another example of starch occurring in dental calculus came from a Roman skeleton from York. Here also I found evidence of starchy foods in all the calculus samples analysed. The photo is particularly interesting, because starches can be seen to be partially degraded. This could be because the starch is partially broken down through the salivary amylase which attacks it as soon as it enters the mouth, or it might hold a clue to a certain type of food preparation.

A group of Victorian skeletons from the St Barnabas Church Crypt in Kensington, London, all had the same kind of starch in their dental calculus. These small angular starches could come from a range of different plants, though root or tuber such as potato can be ruled out, as can any of the cereals.

Future directions

Potential uses of starch and phytolith analyses include accessing pre-agricultural diet where mesolithic or earlier skeletons survive. In the case of more recent material, studies of gender, age or social class related differences in diet can be explored, as well as any variations in diet that may indicate a change in food availability, perhaps, for example, as a result of food shortages or famine.

Where human or animal skeletal material is found, it may still be the case that as part of a cleaning process, dental calculus is removed and discarded. However, it is becoming fast apparent that dental calculus is not waste material, but rather that it can be a source of direct, detailed and comprehensive information on ancient diet from any period. Consequently dental calculus should be preserved in its entirety, not only as part of the pathology of the skeleton, but also in its own right, much as, for example, a human coprolite might be. Analytical methods are constantly developing, and while now it is possible to identify plant types consumed from an extract of a person's dental calculus, even more detailed analyses may be just around the corner.

In order to take the starch and phytolith work further, a reference collection is needed, as identification is carried out mostly through morphological comparison. This enables genus level identification in the case of starches and more specific identification for phytoliths. A grant from the Heritage Council of Ireland has enabled a reference collection of samples taken from ancient starchy plants to be initiated in collaboration with the National Roads Authority there. Further funding is being sought to extend this work to northern Britain to cover not only starches but also phytoliths.

It is always nice to see a way in which archaeology can be used not only to answer our questions about the past, but also to contribute something finite to today; a better understanding of the use of Britain's extensive native sources of foods, starchy and otherwise, at a time when carbon footprints and food shortages of some of the most important starchy foods in the world such as rice are in the news virtually every day, is both timely and constructive. Though it is dependent on gaining funding, it is hoped that a database and reference collection of both phytoliths and starches can be created to enable this fascinating and useful work to develop.

See "Food for thought: starch in Mesolithic diet", by K Hardy, Mesolithic Miscellany 18.2 (2007), 2–11 and "Starch granules, dental calculus and new perspectives on ancient diet", by K Hardy et al, Journal of Archaeological Science 36 (2008), 248–55. The many who have helped develop this work include Les Copeland and Tony Blakeney (University of Sydney), Jennifer Kirkham (Leeds Dental Unit), Matthew Collins, Allan Hall, Hannah Koon (University of York) and Barry McCleary (Megazyme International). Samples have kindly been provided by Don Brothwell, Martin Carver, Cecily Spall (Tarbat), Nicky Milner and Chantal Conneller (Star Carr), Sachichiro Omura (Kaman Kalehöyük, Turkey), Richard Wrangham (Kibale chimpanzee project, Harvard University), Oliver Craig (University of York) and Steven Birch, George Kozikowski and Martin Wildgoose (High Pasture Cave). Francesc Burjachs Casas (ICREA) identified the Pinus pollen. Linda Henderson and George Kozikowski are also thanked for their help with plant collection and identifications in Skye. Funding from the Heritage Council of Ireland, 2008 archaeology grants programme was obtained with James Eogan, National Roads Authority Ireland and Meriel McClatchie. Barbara Tjikatu and family are thanked for collecting and processing grass seeds in Central Australia and for photography consent. Karen Hardy is an ICREA research professor at the Universitat Autònoma de Barcelona, Spain.

See also: In Ray Mears' Wild Food (BBC2 2007, see Books Nov/Dec 2007) Ray Mears and Gordon Hillman explored the rich wild foods available in Britain. The author's research holds out the possibility of being able to identify which foods were actually consumed in the past.

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