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Zeer Pot (Pot-in-pot refrigerator)

The Task: Manufacture and supply an innovative earthenware cooling system to preserve perishable foods in developing countries with arid climates.

The solution: a cheap technique for food preservation, M. B. Abba. To help farmers in impoverished rural Nigeria, 2000 Rolex Award winner Mohammed Bah Abba has developed an inexpensive food preservation technique.

Mohammed Bah Abba

Northern Nigeria is an impoverished region where people in rural communities eke out a living from subsistence farming. With no electricity, and therefore no refrigeration, perishable foods spoil within days. Such spoilage causes disease and loss of income for needy farmers, who are forced to sell their produce daily. Nigerian teacher Mohammed Bah Abba was motivated by his concern for the rural poor and by his interest in indigenous African technology to seek a practical, local solution to these problems. His extremely simple and inexpensive earthenware "pot-in-pot" cooling device, based on a principle of physics already known in ancient Egypt, is revolutionising lives in this semi-desert area.

Low-tech Solution

The art of pottery is deeply rooted in African culture. In northern Nigeria, earthenware pots have been used since ancient times as cooking and water storage vessels, coffins, wardrobes and banks. Today, these clay pots are almost extinct, replaced by aluminum containers and more modern methods of burying the dead, storing clothes and saving money.

Born in 1964 into a family of pot makers and raised in the rural north, Mohammed Bah Abba was familiar from an early age with the various practical and symbolic uses of traditional clay pots, and learned as a child the rudiments of pottery. Subsequently studying biology, chemistry and geology at school, he unraveled the technical puzzle that led him years later to develop the "pot-in-pot preservation/cooling system".

He was selected as a Rolex Laureate in 2000 for this ingenious technique that requires no external energy supply to preserve fruit, vegetables and other perishables in hot, arid climates. The pot-in-pot cooling system, a kind of "desert refrigerator", helps subsistence farmers by reducing food spoilage and waste and thus increasing their income and limiting the health hazards of decaying foods. Abba says he developed the pot-in-pot "to help the rural poor in a cost-effective, participatory and sustainable way".
 
 The pot-in-pot consists of two earthenware pots of different diameters, one placed inside the other. The space between the two pots is filled with wet sand that is kept constantly moist, thereby keeping both pots damp. Fruit, vegetables and other items such as soft drinks are put in the smaller inner pot, which is covered with a damp cloth. The phenomenon that occurs is based on a simple principle of physics: the water contained in the sand between the two pots evaporates towards the outer surface of the larger pot where the drier outside air is circulating. By virtue of the laws of thermodynamics, the evaporation process automatically causes a drop in temperature of several degrees, cooling the inner container, destroying harmful micro-organisms and preserving the perishable foods inside.

Worldwide Technique

The principle of physics used by the pot-in-pot is present in nature itself. A panting dog, for example, uses the same process, losing heat through its tongue. It is also well known by humans in arid countries. Indeed, the roots of innovation spread wide and deep, and Abba’s pot-in-pot is one of several ingenious applications of cooling by evaporation.
 
 The city of Qena in Upper Egypt is renowned for its porous-clay cooling vessels – a tradition spanning more than three millennia. In Burkina Faso, the Jula people’s traditional jars are sometimes soaked in water before goods are stored in them, so that they stay cool by evaporation. This single-pot design is similar to the pot-in-pot, but less efficient.
 
 In India, street vendors often cool fruit or drinks for their customers by suspending bags of produce in a porous clay container. Also in India, a rectangular enclosure of wet bricks is used to preserve foodstuffs from heat. Water seeps slowly through the porous bricks, evaporating from the surface and keeping the entire structure cool. The Pundjab Agricultural University in Ludhiana has recently tested an improved version of this system, which is closer to the pot-in-pot than any other device. It uses double-brick walls, with wet sand between them. The sand is kept wet, and the entire chamber is covered with a moist mat. Fruit and vegetables inside the chamber are maintained at temperatures below 20° C.
 
 In 1992, laboratory experiments to measure the temperature drop in a two-pot design, where a small clay receptacle is placed within another receptacle filled with water, were carried out at the University of Benin City by Nigerian professor Victor Aimiuwu. He found that the device had good cooling properties, remaining up to 14 degrees cooler than the surrounding environment.

Putting theory into practice

Still, among all the similar devices and traditional cooling pots, there is nothing quite like the pot-in-pot with its unique combination of simplicity and effectiveness. In fact, the Nigerian teacher’s project shows how, for the Rolex Awards, originality is far more than a bright idea – it means turning an inspiration into a concrete achievement with a major impact.
 
 "Mohammed Bah Abba won a Rolex Award not simply because he designed the pot-in-pot. He overcame obstacles to produce and distribute it, and also ensured that it could be bought for an affordable price by the people who need it," says Rebecca Irvin, head of the Rolex Awards Secretariat in Geneva.
 
 To understand the relevance of Abba’s Rolex Award-winning project, it is necessary to look at the geography of northern Nigeria and the restricted lives led by the people. This region is primarily a semi-desert scrubland inhabited by a large, mostly agriculture-based population, the majority of whom live in abject poverty. Polygamy is a dominant feature of the family structure, and women, living in purdah, are confined to their homes and seriously disadvantaged in terms of health care, education and employment opportunities. Young girls are particularly enslaved because they are forced to go out each day and rapidly sell food that would otherwise perish, in order to add to the meager family income.
 
 A key reason for the pot-in-pot’s success is the lack of electricity in most of the northern rural communities, for without electricity there can be no refrigeration. Even in towns and cities the power supply is erratic. Most of the urban poor cannot even afford refrigerators.

Personal Inspiration

In the context of an economically drained nation facing severe communication, transport and utility problems, Abba set out to try and help improve the ailing economy. He became a lecturer in business studies at Jigawa State Polytechnic in Dutse in 1990. When not teaching, Abba serves as a consultant to the regional United Nations Development Program (UNDP) in Jigawa, organizing community activities and giving seminars. A staunch supporter of women’s rights, he is also a consultant with the state’s Ministry for Women Affairs and Social Mobilization.
 
 These consultancies brought Abba in close contact with rural communities, where he observed the extreme hardships suffered by subsistence farmers and their families. "Through these observations, I became motivated to revitalize earthen pot usage and extend the life of perishable foods," he explains.
 
 Abba’s first trials of the pot-in-pot proved successful. Eggplants, for example, stayed fresh for 27 days instead of three, and tomatoes and peppers lasted for three weeks or more. African spinach, which usually spoils after a day, remained edible after 12 days in the pot-in-pot.
 
 The enterprising teacher persistently refined his invention for two years between 1995 and 1997. He then tapped into the large unemployed local workforce and hired skilled pot makers to mass produce the first batch of 5,000 pot-in-pots. Manufacturing these devices at his own expense, he began distributing them for free to five villages in Jigawa. For this initial phase of his project, he received limited financial backing from his brother and assistance in the form of transportation, fuel and labor from the UNDP, the regional government, a local women’s development group and the Jigawa State Polytechnic.
 
 In 1999, Abba supplied another dozen local villages with 7,000 pots, again at his expense. Sold for between US$2 for the smaller pot-in-pots and US$4 for the bigger version, the pot-in-pot stays affordable, while proceeds from sales help finance manufacturing and distribution costs.

However, one of the biggest obstacles faced by the project was educating the villagers about this simple technology. Abba devised an educational campaign tailored to village life and the illiterate population, featuring a video-recorded play by local actors who dramatize the benefits of the desert refrigerator. Abba began showing the video in villages using a makeshift cloth screen and a portable projector and generator. "Nightfall is best," he comments, "because this is when farmers head home and are keen to watch an entertaining presentation."
 
 

n 2002, with Abba’s approval, the Intermediate Technology Development Group (ITDG) and the University of Al Fashir carried out experiments in Sudan to assess the performances of the pot-in-pot in food conservation. The excellent results led the Women’s Association for Earthenware Manufacturing in Darfur to manufacture their own pot-in-pots, called zeer in Arabic.
 
 As of early 2005, Abba had distributed a total of 91,795 pot-in-pots. "My life has greatly changed since receiving the Rolex Award," he says.

Transforming rural life

The impact of the pot-in-pot on individuals’ lives is overwhelming. "Farmers are now able to sell on demand rather than ‘rush sell’ because of spoilage," says Abba, "and income levels have noticeably risen. Married women also have an important stake in the process, as they can sell food from their homes and overcome their age-old dependency on their husbands as the sole providers." In turn and, perhaps most significantly for the advancement of the female population, Abba’s invention liberates girls from having to hawk food each day. Instead, they are now free to attend school and the number of girls enrolling in village primary schools is rising.
 
 These factors, coupled with the effect that the pot-in-pot has had in stemming disease, are, in Abba’s words, making "the pot-in-pot a tangible and exciting solution to a severe local problem."
 
 Well known for his dedication, Abba is also praised for his concern with the social and economic development of his fellow Nigerians. "Mr Abba cares for the progress of society in general," says Mrs Hadiza Abdulwahab, president of the local Society for Women Empowerment and Development.
 
 The permanent secretary of the State Ministry of Women Affairs and Social Mobilization, Mrs. Rabi Umar, agrees. She believes that Abba has been "selfless and tireless" in his efforts to make his project succeed. Summing up his work, she says: "The pot-in-pot project is the first to use simple cultural solutions to address the primary needs of the rural northern Nigerian population, for whom the basic necessities of life are nearly non-existent."

The pot-in-pot refrigerator, also known as a Zeer pot is a way of keeping food cool without electricity.

A clay pot is placed in a larger clay pot with wet sand in between, and a wet cloth on top. In this way, food can be kept fresh for much longer in a hot climate.

According to National Geographic, a Zeer pot is "a storage container that's essentially two nested clay pots with a narrow gap between them filled with sand. The sand gets soaked with water, which, as it evaporates, chills the inner container so effectively that food that would normally spoil in two days can last two weeks."

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