Storing Grains with Reduced Energy Consumption: Could Historical Practices Illuminate Our Future?

[Article issu de The Conversation écrit par Anna Valduriez – Cheffe de projet de recherche participative: stockage de denrées alimentaires (pour le futur, à partir de méthodes ancestrales), Inrae – Dominique Desclaux – Chercheure en Agronomie et Génétique, Inrae – Jean-Michel Savoie – chercheur, Inrae – Marie-Françoise Samson – Chercheuse en biochimie alimentaire, Inrae – Maxime Guillaume – chercheur, Institut national de recherches archéologiques préventives (INRAP) – Tanguy Wibaut – chercheur, Institut national de recherches archéologiques préventives (INRAP)]

In the case of food, it is recommended to store them at low temperature to limit the proliferation of bacteria and other microorganisms. Thus, the average electricity consumption of a domestic refrigerator (300 to 500 kWh/year) represents a quarter of household energy expenditure. And if this is the case for the ingredients that we keep at home, the large -scale needs on the producers' side are all the more important.

Here, it is storage of grains (cereals and oleoproteaginous), which constitute the basis of our diet, which is discussed. Can storage in the Mediterranean region, from Neolithic to the present day, enlighten us on how to consider the storage of the future?

Storage, a practice from the Neolithic

From the Neolithic, humanity practiced underground storage and in an attic, and this, in an individual or collective way. This method remains active punctually in certain regions of the world, as in Sudan, or even in Morocco and Tunisia.

In France, despite some variations linked to geographic periods and areas, these buried silos have generally been dug in the form of a variable size, which inrap archaeologists regularly find, in particular on the medieval sites of Thuir (Pyrénées-Orientales), Pennautier and Montreal (Aude).

It is towards the end of the Middle Ages that underground storage is abandoned in France in favor of the grain attic. The explanations for this evolution remain of the order of the hypothesis: one of them is due to a centralization of power requiring control of the quantities of wheat and other cereals that does not allow the buried silo.

It's only in the XIX^e A century than curiosity for the underground storage method reappeared and was the subject of new studies by agronomists.

However, this momentum was slowed down by the context of the First World War. In the early 1930s, the wheat overproduction crisis gave birth to cooperatives and the trading market system to regulate production.

Part of the wheat crops are delivered to cooperative storage centers by producers in order to ensure the leveling of sales and market stabilization. These are the first major industrial silos, which developed mainly in the 1950s.

Increasingly sophisticated silos

From now on, the grains are mainly brought after harvesting to stocker organizations, but it is estimated in France that 53 % of farmers also store on the farm.

Storage which must guarantee good grain preservation, temperature and humidity are controlled in silos: this control most often involves ventilation, but also by forced cooling in order to avoid the proliferation of insects and mold. Authorized insecticides are often applied upon receipt of harvests and a gas gassing with phosphine (pH3) is sometimes practiced, under very secure conditions, to prevent invasions of insects.

In concrete or metal, cylindrical or rectangular, the silos visible in the south of France vary in size and capacity: at a height of 25 to 30 meters, they can accommodate 200 to 12,000 tonnes per cell.

The highest silo in the world, Swissmill, is located in Zurich: 118 meters high, it can house 40,000 tonnes of wheat. The more massive the silos, the more the energy needs to ensure their filling and ventilation are substantial … What the increase in temperatures does not help, generating an almost continuous ventilation need. Energy consumption which is added to the environmental impacts linked to the transport of cereals along the production chain.

Some farmers equip themselves with silos on the farm, but there are many who store in “big bags”, flexible bags of large capacity (from 500 kg to 2 tonnes) generally made of polypropylene. Also developed “Big Bag Nox”, double layer airtights, which create a physical barrier preventing the entry of pests: in parallel, the injection of CO₂ Kill those already present by depriving them of oxygen. In the same idea, we find the hermetic silos, which have experienced a low development in France because of their cost.

These techniques use the same principles of storage in modified atmosphere as those prevailing for medieval underground silos.

Storage at the challenge of future crises

Climate change, political conflicts, energy attacks and pandemics threaten food security, not only in terms of production, but also storage. The latter, if defaulting, is also an important source of waste and loss of foodstuffs.

It is from this observation that the research carried out by the Locastock collective follows. Different actors experience it together and develop a prospective reflection around the issue of grains and other food storage.

Thus archaeologists attempt to find conservation techniques within silos rendered hermetic. Organic cereal producers are testing underground storage. In parallel, geneticists and agronomists provide genetic diversity, and pathologists and biochemists analyze the health, nutritional and organoleptic quality of the grains stored once they are recovered after several months passed underground. Finally, a disadvantaged neighborhood management interested in the storage of foodstuffs as well as a project manager facilitating science-society links are also associated so that the issues are not discussed only from a only technical point of view.

This work of the Locastock project aims to imagine and experiment with resilient storage of agricultural and food productions under clean, healthy, loyal, economical conditions, without impact on the environment and adapted to the current context, as well as to define to what extent ancestral techniques can contribute to providing responses to the challenges of the present and the future.