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The pot-in-pot refrigerator or zeer (Arabic: الزير) and its manufacturing process was engineered by Mohammed Bah Abba, a Nigerian teacher from a family of pot-makers, who patented a pot-in-pot refrigerator in 1995 to help Sudanese families preserve food. Bah Abba was awarded the $75,000 Rolex Award for Enterprise in 2000 and the World Shell Award for Sustainable Development in 2001, and elected to the Ashoka Fellowship in 2008 for its development. It is a refrigeration device which keeps food cool without electricity by using evaporative cooling. A porous outer earthenware pot, lined with wet sand, contains an inner pot (which can be glazed to prevent penetration by the liquid) within which the food is placed – the evaporation of the outer liquid draws heat from the inner pot. The device can be used to cool any substances such as water, foods or temperature sensitive drugs.
There is some evidence that evaporative cooling was used as early as the Old Kingdom of Egypt, around 2500 B.C. Frescos show slaves fanning water jars, which would increase air flow around the porous jars and aid evaporation, cooling the contents. These jars exist even today and are called “zeer”, hence the name of the pot cooler. Many earthenware pots were discovered in Indus Valley Civilization around 3000 BC which were probably used for storing as well as cooling water similar to present days ghara or matki used in India and Pakistan.
Despite being developed in Northern Africa, the technology appears to have been forgotten with the advent of modern electrical refrigerators. However in the Indian Subcontinent, ghara, matka and surahi, which are different types of earthenware water pots are used to cool water. In, Spain the popular botijos, porous clay containers to keep and to cool water, have been in use for centuries (and are still relatively widespread), favored by the low Mediterranean climate; locally the cooling effect is known as “botijo effect”.
The idea of using the physical principle that cools water in these traditional containers was re-engineered by Mohammed Bah Abba so that perishables such as food could be stored as well as water. Bah Abba’s desire to help poor Nigerian women led to his idea of a new design and coupled this with low cost production techniques.