The technique of using evaporative cooling with clay pots for food preservation was re-discovered 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 for its development.
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), working in a similar way as the pot-in-pot refrigerator.
|Food||Unrefrigerated shelf life||Shelf life with zeer|
|Carrots||4 days||20 days|
|Eggplant||1-2 days||21 days|
|Guava||2 days||20 days|
|Meat||<1 day||~14 days|
|Okra||4 days||17 days|
|Rocket||1 day||5 days|
|Tomatoes||2 days||20 days|
How to Make a Pot in a Pot Refrigerator
Keeping the sand moist all the time enables evaporation to cool the produce kept inside the inner pot.This enables the storage of freshly grown vegetables to last much longer than usual in a hot climate. It is also great for using at a picnic or outdoor meal where there is no electricity outside but food or drinks need to be kept cool. Here is how to make your own.
- Obtain two large clay or terracotta pots. One pot must be smaller than the other pot. Check that the smaller pot fits inside the larger and that there is a space around it of at least one centimetre, up to three centimetres.
- 2Fill in any holes at the base of the pots. Use clay, large pebbles, cork, a homemade paste - anything suitable to hand to fill the hole. If you leave the holes open, the water will enter the inner pot and will also run out of the larger pot, making the fridge ineffective.
- Putty or duct tape can plug the hole.
- 3Fill the base of the larger pot with coarse sand. Fill about 2.5cm/1 inch deep, and only fill to a height that will ensure the smaller pot sits even in height with the larger pot.
- 4Place the small clay pot into the large pot. Arrange its base flat on top of the lower layer of sand.
- 5Fill all around the small pot with sand. Fill it almost all the way, except for leaving a small gap at the top.
- 6Pour cold water over the sand. Do this until the sand is completely soaked and unable to take any more water. As you pour, do so gradually in order to give the water time to soak into the terracotta.
- 7Take a cloth, tea towel or towel and dip it into water. Place it over the top of the inner pot so that it covers it completely.
- Wet hessian or similar fabric also works well.
- 8Allow the inner pot to cool down. If you have a thermometer, you can use this, otherwise test the temperature with your hands.
- 9Keep the pot-in-pot refrigerator in a dry, ventilated space for the water to evaporate effectively towards the outside.
- 10Place vegetables or other items inside for storage. You will need to keep checking regularly for the dampness of the sand. Pour in more water as it becomes drier to keep it well moistened. Usually this will need to be done twice a day.
- You can add food or drinks to the pot-in-pot refrigerator if you're having an outdoor party or picnic. Make one for the drinks and one for the food if you have a lot of