The pots can be produced locally by artisans, and made from local clays. The pots allow people to store tomatoes and other produce for 21 days or more instead of three or four.
The Zeer pot, also known as simply a Zeer (in Arabic) or a pot-in-pot refrigerator, was developed in Africa. It was created for people to store food for longer periods of time. There are two pots, a small ceramic pot inside of a larger ceramic pot. Between the two pots there is sand, and when water is pored on the sand it makes the inner pot colder via evaporation (evaporative cooling). This is used like a refrigerator to keep things cold.
An article in the online Science in Africa explains: "The zeer is a large pot inside which fits another smaller pot with a clay lid. The space between the two pots is filled with sand, creating an insulating layer around the inner pot. The sand is then kept damp by adding water at regular intervals — generally twice a day — reducing the temperature within the inner pot."
An analysis of this technology can be found here.
See also
- Zeer pot refrigeration (design) - detailed design issues and modeling.