As spring sprung and we could no longer keep food cold outside or use ice that we froze outside for coolers, I began to research off grid refrigeration options. I saw a lot of people posting pictures of a little device called a zeer pot. It’s not a new invention. It’s actually been around for thousands of years. It works on the simple principle of evaporation. Sand between two clay pots (nested together) is moistened with water. Food is placed into the inside pot and a wet cloth is placed on top. Supposedly, this is the answer to my prayers of keeping food cold with no electricity at all! I’m saying this a little facetiously after being told many times that this would work for me. Of course, these people are only repeating claims that a zeer pot is the answer to refrigeration without electricity.
When something sounds to good to be true, I am always a little skeptical. So I set out to find out the truth about these “miracle” pots. If all the claims that I heard were true, then I would definitely make one! But common sense told me that I would probably be disappointed. It gets hot in the summer in Arkansas! July and August are our hottest months with many days in the high 90’s and 100’s. How are two clay pots going to keep my food cold? The answer is that they are not.
The preferred refrigerator temperature is between 35 and 38 degrees. This is our general expectation when we open the fridge and take something out. We want it to be cold! But it has a controlled environment, powered by electricity, that keeps the food cold. The zeer pot depends on outside temperatures and relative humidity. Evaporative cooling works because the transition of liquid water to water vapor, allows the dry air around to be cooled. So as the water evaporates out of the sand and wet cloth, it cools the air inside the zeer pot. But by how much? Well this depends on the environment it is in. At 0% relative humidity, the device functions its best. There is no water in the air, so the evaporation process in the pot happens quickly and efficiently. You may have to add water more regularly, but your work will be rewarded. At 65 degrees outside and 0% humidity, you may be able to approach refrigerator temperatures.
But I don’t live in the desert. I live in the Ozarks. Our high today on July 6, was 86 degrees. The relative humidity was 83%. Not really the conditions that I’m looking for when using a zeer pot. With these conditions, the best I could do would be about a 6 degree difference. So, I now understand why we only see fruits and vegetables in pictures of zeer pots. We don’t see them filled with leftovers, meats, and dairy products because most of us don’t live with 0% humidity. It’s a great idea, but it is not the miracle off grid refrigerator that people make it out to be.