Friday, 19 December 2014

How did we store foods in the past?

Experimental pit storage of cereals 

As we come towards the end of the year in temperate climatic regions of the world, we turn to stored foods to provide variety during the cold winter months. Many plants ripen only at certain times of the year. To make use of these plants throughout the whole year, we must find ways of storing them. The storage of plant foods was an important activity in many past societies, and there is abundant archaeological evidence for the storage of cereals in particular.

Cereal storage is important for the safe-keeping of both seed corn (for planting the following year) and ‘excess’ produce. Storage facilities for cereals can be located underground or above ground.  It is suggested that hermetic, or air-tight, storage in underground pits was the most widespread method throughout the world for the conservation of cereals in bulk prior to the 18th century (Sigaut 1988). Experimental work and other studies (e.g. Reynolds 1979; Cunliffe 1992) confirm that no form of internal lining is required, but an airtight seal across the top of the pit is necessary. When the pit is sealed, micro-floral growth, which begins to infect the grain against the pit wall, soon consumes the trapped oxygen, replacing it with carbon dioxide. Once a critical level is reached, further decay is prevented, and the bulk of the grain remains fresh until the seal is broken. 

As part of my own experimental work, I filled a large pit with cereal grains, sealed the pit carefully, and then returned one year later to retrieve the cereals (see image above, which shows work with students at University College London). When we opened up the pit again, the smell was extraordinarily bad, but this was just the rotted grain around the edges of the pit. Much to our delight, the majority of the grain was in excellent condition and perfectly usable.

In archaeology, we often interpret the presence of cereal remains in pits as evidence for the storage of surplus grain. But the mere presence of cereal remains does not automatically indicate that these pits were used for cereal storage. Pits may instead have been used for the deposition of waste, including crop-processing and cooking waste. Charred cereals may also have been carefully placed into the pits, perhaps as part of a symbolic deposition. There can be a variety of explanations for the recovery of cereals in pits, rather than assuming storage.

Overground storage structure, northern Spain
Irish law texts of the seventh and eighth centuries AD indicate that tightly-woven wicker baskets, as well as bags, perhaps of leather, were used as containers for the transport or temporary storage of grain (Kelly 1997). Longer-term storage of cereals also took place in above-ground or ventilated areas, which would have allowed easier access to cereals than underground storage, because the latter requires the breaking of an air-tight seal each time the cereals are to be accessed. There is archaeological evidence for the remains of structures that could have functioned as raised granaries. These include ‘four-posters’, whose only surviving evidence is the traces of four posts that supported the above-ground storage area (pictured above is an elaborate example that I observed during ethnographic fieldwork in northern Spain). 

But again it is difficult to demonstrate that four-posters, for example, were actually used in this way. The cereals stored in such structures would not have been preserved unless they were subject to charring, waterlogging or another process that will enable the preservation of cereal remains. Instead, we are just left with the remains of a number of posts and occasionally a small quantity of food or other remains, which cannot be used to securely interpret such structures as raised granaries. It is clear, therefore, that we need to be careful when trying to identify cereal storage in the archaeological record.

Cunliffe B (1992) Pits, preconceptions and propitiation in the British Iron Age. Oxford Journal of Archaeology 11(1): 69-83. 

Kelly F (1997) Early Irish farming: a study based mainly on the law-texts of the 7th and 8th centuries AD. Dublin: Dublin Institute for Advanced Studies. 

Reynolds PJ (1979) Iron-Age farm: the Butser experiment. London: Colonnade.

Sigaut F (1988) A method for identifying grain storage techniques and its application for European agricultural history. Tools and tillage 6(1): 3-32.

Monday, 24 November 2014

Routine activities and everyday archaeobotany

A new paper that I wrote with colleagues based at the Institute of Archaeology, University College London has just been published. The paper is titled “Routine activities, tertiary refuse and labor organization: social inferences from everyday archaeobotany”, and my co-authors are leading archaeobotanists Prof. Dorian Fuller and Dr Chris Stevens. The paper is published in an exciting new monograph, “Ancient plants and people: contemporary trends in archaeobotany” by the University of Arizona Press. The monograph contains 14 papers that present a wide-angle view of the current state of archaeobotanical research, methods and theories across the world. The contributors discuss methodological issues and engage in debates on a wide range of topics, from plant utilization in hunter-gatherer and agriculturalist societies to uses of ancient DNA. “Ancient plants and people” provides a global perspective on archaeobotanical research, with a particular focus on the sophisticated interplay between the use of plants and their social and environmental context.

My paper with Prof. Fuller and Dr Stevens re-considers relationships between archaeological contexts and their archaeobotanical assemblages, arguing that many assemblages do not reflect the function of the context itself, but instead represent incidental loss or waste disposal from recurrent, routine activities. One of the remarkable features that every archaeobotanist will have experienced is the uniformity of samples from across given sites, cultures and phases. The recurrence of the same species and parts of species (e.g. grains, seeds, nutshells, chaff, etc.), whether of wild foods, crops or weeds, can often be detected in a narrow range of proportions. What such a pattern implies is that, within any region during a defined period of time, the same type of material is not only routinely being burned but also, in all probability, is being produced by a limited number of well-defined activities, and such activities are being repeated on a continuous basis.

The nature of most archaeobotanical evidence is such that its final resting place is usually only tenuously, if at all, connected to the activities that produced it. Only very rarely will archaeobotanical assemblages contribute to studies of spatial patterning and activity areas on archaeological sites, except perhaps at a coarse scale on the very largest sites. Despite their tertiary nature, however, the recurrent patterns of archaeobotanical assemblages across sites reflect recurrent practices in the past: the routine. As such, they provide an important window on traditions of daily household labour. Through consideration of the composition (rather than the context) of archaeobotanical assemblages, we reveal new insights into social organisation through case studies from North-West Pakistan, South India, Southern Britain and Ireland, and we also address the vexed issue of the role of dung burning in the creation of Old World seed assemblages. The monograph can be purchased via the publisher’s website. 

Fuller DQ, Stevens C, McClatchie M (2014) Routine activities, tertiary refuse and labor organization: social inferences from everyday archaeobotany, pp 174–217. In Madella M, Lancelotti C, Savard M (eds), Ancient plants and people: contemporary trends in archaeobotany. Tuscon, University of Arizona Press

Tuesday, 28 October 2014

Nuts about hazelnuts: the enduring tradition of foraging in Ireland

Hazelnuts (image via Orkney Jar)

Hazelnuts have been an important food resource in Ireland for thousands of years. Hazelnuts usually ripen during autumn and are therefore seasonal, but hazelnuts are also easily storable, and so can be kept for eating throughout the year. The nuts provide a highly nutritious foodstuff, being rich in monounsaturated fats. They can be eaten whole, or ground into flour or meal. Hazelnuts are also relatively easy to process using simple tools; the nutshell can be cracked open using a sharp stone, or by placing the hazelnut on a hard surface or stone, and then striking the shell with another stone.

While the actual nuts rarely survive in the archaeological record, hazelnut shell is often recorded. Hazelnut shell is relatively easily identified by archaeobotanists. The shape of the nutshell is very distinctive, and although the nutshell is woody, it is smooth in section when compared with wood charcoal. Hazelnut shell can be preserved through a variety of mechanisms, but charring is the most commonly encountered process in Ireland. In order for charring to occur, the plant material must come into contact with fire. Nutshell represents waste and is perhaps more likely to come into contact with fire and become preserved, when compared with other plants. For example, the nutshell can be utilised as fuel or simply disposed of in fires to reduce its mass. Other food sources, such as cereal grains, are less likely to enter a fire, as the grains will become unusable if charred (Jones 2000).

Charred hazelnut shell
While we often associate gathered foods with prehistoric societies (McComb and Simpson 1999), archaeobotanical evidence clearly demonstrates that foraging was an important activity right into the historic period. A recent study of plant foods consumed by Ireland’s earliest hunter-gatherer communities, during the Mesolithic period (8000-4000 BC), revealed that hazelnut remains were commonly found at excavations, sometimes in very large quantities (Warren et al. 2014). Although farming was introduced into Ireland during the Neolithic period (4000-2500 BC), gathered foods remained important; a study of plant remains from Neolithic excavations in Ireland found that hazelnut shell was present at 87% of sites (McClatchie et al. 2014). From the Bronze Age, it does appear that cultivated foods became increasingly important at the expense of gathered foods, but foraging continued to be undertaken. A recent study of plant remains from early medieval Ireland (AD 400-1100), for example, found that hazelnut shell was recorded at 40% of sites (McCormick et al. 2014), highlighting that gathered foods continued to play an important role, even in societies heavily involved in farming. There is a long history of hazelnut gathering and consumption in Ireland, and it looks set to continue, helped by a revived interest in foraging that has developed over recent years.

Jones G (2000) Evaluating the importance of cultivation and collecting in Neolithic Britain, pp. 79-84. In Fairbairn AS (ed.), Plants in Neolithic Britain and beyond. Neolithic Studies Group Seminar Papers 5. Oxford, Oxbow.  
McClatchie M, McCormick F, Kerr T, O'Sullivan A (2014) Early medieval farming and food production: a review of the archaeobotanical evidence from archaeological excavations in Ireland. Vegetation History and Archaeobotany. DOI: 10.1007/s00334-014-0478-7.

McComb AMG, Simpson D (1999) The wild bunch: exploitation of the hazel in prehistoric Ireland. Ulster Journal of Archaeology 58, 1-16.

McCormick F, Kerr TR, McClatchie M, O'Sullivan A (2014) Early medieval agriculture,livestock and cereal production in Ireland, AD 400–1100. British Archaeological Reports, International Series 2647. Oxford, Archaeopress.

Warren G, Davis S, McClatchie M, Sands R (2014) The potential role of humans in structuring the wooded landscapes of Mesolithic Ireland: a review of data and discussion of approaches. Vegetation History and Archaeobotany 23(5): 629–646.

Wednesday, 24 September 2014

Recreating early medieval oat biscuits: experimental archaeology

Cooking oat biscuits at the edge of the fire

Experimental archaeology can help us understand how people carried out daily tasks in the past, revealing potential processes and social interactions involved in various activities. It’s a very useful, hands-on way for students to gain new insights into past societies. At the beginning of this month, I spent a very enjoyable day teaching undergraduate students about ancient crops and foods as part of the UCD School of Archaeology module “Experimental Archaeology and Ancient Technologies”. We are very lucky at UCD to have an on-campus area to undertake our experimental activities, the UCD Centre for Experimental Archaeology and Ancient Technologies. We can re-construct houses, build pottery kilns, undertake metalworking and many other tasks, all on campus!
As part of the “Experimental Archaeology and Ancient Technologies” module, we spent a full day with students on food-related activities. We processed crops from sheaf to grain using very basic implements, ground the grain into flour using saddle and rotary quern stones, and made a variety of stews and other food products.
One of our activities was the production of oat biscuits. We were inspired by the extraordinary find from Mick Monk and his team excavating Lisleagh ringfort (early medieval enclosed settlement) in Co. Cork (McLaren et al. 2004). They unearthed the charred remains of an oat biscuit, which was analysed by archaeo-chemist Frances McLaren. She found that the biscuit remains consisted of oatmeal and a low-fat dairy product, perhaps whey. The inclusion of whey would have produced a low-fat biscuit that could have been stored for a relatively long period. Whey is the liquid remaining after milk has been curdled and strained to produce curds for cheese.
Curds (left), whey (centre) and oat dough for biscuits (right)
First of all, we used the quern stones to grind oat grains into flour. The oat grains were kindly donated by Flahavan’s oat mill in Co. Waterford. We then needed to add a little whey to the oat flour. The traditional method of converting fresh milk to curds and whey is to leave the milk out for a few days. We used the method of heating the milk and adding an acidic substance (e.g. vinegar).
After separating the curds from the whey (using a muslin cloth), we added a little whey to the oat flour to make a wet dough. We took golf-ball sized lumps of the dough and flattened them out with our hands into the shape of oat biscuits. We then cooked the biscuits on a griddle at the edge of a fire for around half an hour. We learnt just how much time is required for non-mechanised food production, which has important implications for understanding how past societies structured their days. We also appreciated that tasty foods can easily be produced using basic ingredients and simple tools.
McLaren F, Monk MA, Sexton R (2004) ‘Burning the biscuit’: evidence from the Lisleagh excavations reveals new secrets twenty years on! Archaeology Ireland 18:18-20.