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.