So, this is a really cool idea I wanted to pass along. The people of Sudan have come up with an innovative way to keep their produce fresh for significantly longer by using these clay refrigeration systems known as Zeer pots. In the severe heat of their country, produce only lasts a couple of days before going bad.
Many people lose half of their crops to spoilage because of a lack of refrigeration, sadly leading starvation for many.
Fortunately, a new method of preserving their crops is being taught, and more and more Sudanese are learning how to keep their produce fresh for up to three weeks longer than they normally could by making and using their own Zeer pots.
I love this idea because it doesn’t require any consumable resources; no gas, no kerosene, no electricity whatsoever. Nothing but nature itself: two clay pots, sand, and water. It works off of evaporative cooling.
What is a Zeer Pot?
A zeer pot, or pot-in-pot cooler, is a simple evaporative cooling device that is basically a primitive refrigerator, one suitable for storing and extending the shelf life of fruit, vegetables and other produce, even leftovers.
Unlike modern evaporative coolers, these ingenious systems use very few components and absolutely no electricity, and are the ideal solution for preserving food or any other materials that require cool temperatures so long as they are used in hot, dry air.
Used throughout the Middle East, Africa and the Asian subcontinent since at least 3,000 BC, zeer pots remain in use today all over the world where refrigeration is needed and electricity is either completely unavailable or just not practical.
How Do Zeer Pots Work?
Zeer pots work on the principle of evaporative cooling. Using nothing more than a couple of pots that can nest one inside the other, and a layer of wet sand between the two, heat can be drawn out of the inner pot as air flows over the unit and the water evaporates, carrying heat with it.
Abiding by easily understood principles of thermodynamics, the inner pot is substantially cooler than the ambient temperature and humidity levels.
All that is needed for this system to work is appropriate atmospheric conditions, a few simple materials, and water to keep the sand wet. So long as all of these requirements can be achieved, zeer pots will provide continuous and effective refrigeration.
Once a zeer pot is properly assembled, and assuming the outside temperatures and relative humidity allow for effective operation, all you need to do to make them work is to thoroughly wet the layer of sand between the two pots and keep it wet, while also covering the top opening of the pots with a wet cloth.
This will necessitate regular though infrequent watering of the sand, but if you are clever it is possible to set up a self-watering or self-refreshing system using a dish of water.
Zeer pots are the picture of simplicity, and can be made with commonly available, dirt cheap materials. But as with most things, a few smart upgrades or careful material selection can dramatically improve performance. We will note these potential enhancements next to each component below:
Porous Outer Pot
The outer pot is the larger of the two pots, and should be made of a rigid but porous material, typically clay. It is essential that water be able to move into and through this clay pot over time because this is what will make the evaporative cooling process work.
The inner pot is the small pot, usually clay, and should be designed in such a way that it will nest snugly within the larger pot with a layer of sand separating them on all sides except the open top. Notably, make sure the rim of the inner pot is level with the outer pot or only poking up just above it for best results.
When it comes to inner pot construction, you have a choice: if you are storing produce that can tolerate higher humidity levels, the inner pot can also be water permeable.
However, if you want to maintain dryer conditions inside the inner pot it should be glazed or coated in a way to prevent water from moving through it.
Simple sand is an essential component of a zeer pot, and facilitates the evaporative process. You can use any sand you want, but you’ll always get better performance if the sand is thoroughly cleaned and sifted end of uniform size so that it can be packed tightly inside the larger outer pot and fill the space completely between it and the inner pot.
Take the time to thoroughly clean and screen your sand for best results!
Water functions as the operative agent for our zeer pot, and when the water is drawn through the sand and evaporates it will chill the inner pot. We recharge and refresh our zeer pot by periodically wetting down the sand on all sides of our cooler. Note that clean, freshwater must be used if the inner pot is water permeable.
However, if the inner pot is completely water-impermeable, you may use non-potable water such as seawater for the purpose. Never, ever use unsafe or questionable water in your zeer pot if the inner pot will allow moisture to reach your food!
A coarse, clean cloth is all that is needed for covering your zeer pot. Wetting the cloth down so that it stays damp but not dripping wet before placing it over the top of both pots will facilitate proper operation and improve performance.
Also, make sure you only ever use clean, drinkable water for wedding down your cloth because it could possibly drip down onto your fruits and veggies inside. You don’t want them contaminated with any germs that could be lurking in the water.
Building the Zeer Pot
Here’s how you can make your own:
1. You need two large terracotta pots, one larger than the other. Plug any holes.
You can use duct tape (on a totally dry pot) or cork to plug holes or waterproof marine epoxy to fix cracks. Remember that the inner pot should be totally water-impermeable if you want to reduce moisture levels.
2. Pour sand into the bottom of the larger pot, enough that when you place the smaller pot inside, its rim is level with the rim of larger pot. There needs to be about an inch of sand, or slightly more, between the smaller pot and the larger one on the sides and bottom.
3. Fill in the gap between the pots with sand, packing it all the way to the rim.
4. Now, pour water over the sand until it begins to just puddle on top. Place the pots in a shady place, to help maintain coolness.
5. Place a damp cloth over the pots to help hold in the cooler temperature.
6. Make sure to add enough water every day to keep the sand moist.
The pots will begin to absorb the water, which will then evaporate causing the pots and their contents to become cooler. Zeer pots really need to be in a low humidity environment to work.
Many Sudanese have multiple pots around their homes, so don’t feel limited to just having one of these!
What are the shortcomings of a zeer pot?
Zeer pots are pretty amazing, but they are not the end all, be all of refrigeration technologies, and even off grid refrigeration technologies.
The first and most obvious shortcoming of a zeer pot for those who have been paying attention is that they are entirely dependent upon ambient conditions and outside temperatures to operate.
In short, the higher the humidity the worse they perform, to the point that merely warm temperatures and extreme humidity might see them fail to function entirely.
The next problem is one that can be rectified through the use of additional zeer pots, but they do have a size limitation. I’ll skip explaining the long and drawn out math, but take my word for it when I say that the maximum capacity of inner pot that you should use if you want a reliably good zeer pot is around 130 to 150 liters.
You can, of course, use smaller zeer pots but if you need more space than that you’ll need to construct a second one or switch to a different technology entirely since they dramatically lose efficiency above that size.
Also, you should not rely on zeer pots to store things for any length of time that rely upon true cold storage to avoid spoilage.
Things like meat, dairy products and certain medicines like insulin and more can be kept reasonably safe for a short period of time using a zeer pot, but you can’t count on them for long-term storage of these goods.
Lastly, even when used in dry conditions and with a water impermeable inner pot, zeer pots are not recommended for goods that require truly dry conditions. Grains, spices, beans, onions, garlic and the like will not do well in a zeer pot.
A city girl learning to homestead on an acre of land in the country. Wife and homeschooling mother of four. Enjoying life, and everything that has to do with self sufficient living.