Several years ago, Mohammed Bah Abba designed an earthenware cooling system (the “pot-in-pot” method) to preserve foods in countries with hot, dry climates. In Northern Nigeria (where Abba is from), no electricity is available and propane refrigeration is prohibitively expensive.
Abba's design includes two clay pots of different sizes, one inside the other. Sand is put in the space between the pots and is kept wet. As the water evaporates toward the outside of the large pot (and toward the dry outside air), the contents of the inside pot are cooled and preserved for days. Evaporation requires energy, which is taken from the heat in the pot. As a result, the temperature drops and the inner container is cooled. The inner pot is covered with a damp cloth and the whole thing is kept in a very dry, ventilated place.
In trials, eggplants stayed fresh for 27 days (compared to three days otherwise); tomatoes and peppers lasted 21 days. African spinach was still edible after 12 days instead of spoiling after one day.
Abba hired unemployed pot makers to produce his cooling systems. He estimates that in Jigawa State, Nigeria, ¾ of rural families use the “Pot-in-pot” system.
The social and economic impacts of the Pot-in-pot technology are enormous. Farmers are now able to sell vegetables on demand instead of immediately after harvest. Married women can sell food from their homes. Girls are able to attend school instead of selling food every day. The whole community experiences less disease from eating spoiled food.
Read more about Abba’s invention in Food Chain, issue 29.
Berkelaar, D. 2005. Where There is No Refrigeration. ECHO Development Notes no. 89