Chapters 8.7

8.7 - Simple clay pot cooler to prevent spoilage

Gryphon Theriault-Loubier, University of Guelph, Canada

Source:https://en.wikipedia.org/wiki/File:Tonkrugk%C3%BChler,_Clay_pot_cooler,_Canari_Frigo.JPG

Suggested citation for this chapter.

Theriault-Loubier,G(2022) Simple clay pot cooler to prevent spoilage. In Farmpedia, The Encyclopedia for Small Scale Farmers. Editor, M.N. Raizada, University of Guelph, Canada. http://www.farmpedia.org

Introduction

It is estimated that between $200-300 million dollars (USD) worth of produce perish each year due to lack of adequate storage infrastructure (Chaurasia, 2005). The reduction of food spoilage is critical to ensuring that developing markets can remain competitive (Tomada, 1992). The pot-in-pot (PiP) storage system is a promising method of providing portable, affordable refrigeration to parts of the world without electricity (Mittal, 2006). The pot is used to preserve vegetarian food in India (Date, 2012), and has been analyzed for its heat transfer properties, with a recorded decrease in temperature of 10.4˚C lower than ambient temperature in low humidity environments (Aimiuwu, 1992). Variations of this technology have been reported in West Africa (Aimiuwu, 2008), India (Date, 2012), and the Middle East (Mittal, 2006). The technology has been reported to be highly effective for storage of various fruits and vegetables including tomatoes, Guavas, Rocket (A leafy green), Okra and Carrots (Longmone 2003; Chaurasia et al. 2005; Odesola and Onyebuchi, 2009) The technology is simple. A smaller pot is placed in a larger pot; the empty space between the pots is then filled with sand. Water is added to saturate the sand - as the water evaporates, it draws heat along with it, cooling the air and contents of the inner pot (Mittal, 2006). The PiP is based on the well-known principle of evaporative cooling. Just as the human body sweats during exposure to heat or while exercising to cool itself, the PIP slowly evaporates water contained in the outer pot, drawing heat with it, to effectively cool the air of the inner pot (Mittal, 2006). Sand acts as an insulator, reducing the amount of water needed to reach the desired temperature (Mittal, 2006). A damp cloth is sometimes put over top of the inner pot. The outer pot should be highly porous and importantly, not glazed. A glazed pot will not allow water to effectively escape the vessel. Conversely, some trials have suggested that the inner pot be glazed or otherwise water-tight so as to prevent the entrance of moisture. This is especially important if the water is not potable.

Possible Benefits

A PiP system is based on revived indigenous knowledge which is easily transferrable, not patented, and extremely low-cost (around $1 per pot). Outer pots could be decorated as a form of branding and designed to be stackable. Many cultures already make and use pots and have sand available.

Critical Analysis

A PiP system would work best in high temperature, low humidity climates. As the humidity rises, the capacity of the water to evaporate, and thereby cool the contents of the second pot, is diminished. Additionally, high temperature and low humidity areas could be prone to drought, and a PiP system requires a constant, though relatively little supply of water. Saltwater could also be used. Unintended sealing of PiPs might trap plant-derived ethylene gas, a hormone which triggers ripening (Barry, 2007); in this situation, the produce could be placed in an ethylene adsorbent bag placed within the PiP. PiPs add shipping weight and bulk and would not likely be carried to market by hand. One might build a larger, semi-permanent structure on a small trailer which could be unloaded or loaded. One such (non-mobile) structure built of double walled brick was found to reduce ambient temperature inside the chamber by up to 14˚C while reducing shrinkage by 15-70% (Chaurasia, 2005).

Picture Based Lesson to Train Farmers

Click on the image to access a higher resolution image as well as lessons adapted for different geographic regions.

For the South Asian version (pictures only, text for you to insert), click this link for lesson 9.7:http://www.sakbooks.com/uploads/8/1/5/7/81574912/9.7_south_asian.pdf

For the East/South Asian version (pictures only, text for you to insert), click this link for lesson 9.7:http://www.sakbooks.com/uploads/8/1/5/7/81574912/9.7e.s.a.pdf

For the Sub-Saharan Africa/Caribbean version (pictures only, text for you to insert), click this link for lesson 9.7:http://www.sakbooks.com/uploads/8/1/5/7/81574912/9.7subsaharan_africa_carribean.pdf

For the Latin-America version (pictures only, text for you to insert), click this link for lesson 9.7:http://www.sakbooks.com/uploads/8/1/5/7/81574912/9.7latin_america.pdf

For North Africa And Middle East version (pictures only, text for you to insert), click this link for lesson Chapter 5. 8.5:http://www.sakbooks.com/uploads/8/1/5/7/81574912/8.5n._africa_middleeast.pdf

Source: MN Raizada and L Smith (2016) A Picture Book of Best Practices for Subsistence Farmers. eBook, University of Guelph Sustainable Agriculture Kit (SAK) Project, June 2016, Guelph, Canada.

Further Information

Pots based on this system (known as zeer pots) can be purchased by visiting Practical Action or by phoning +44 (0) 1926 634400. There are also detailed instructions available for local construction.

Contact Person: Mr. Mohammed Bah Abba – Jigawa State Polytechnic, College of Business and Management Studies, Sani Abacha Way, P.M.B 7040, Dutse, Jigawa State, Nigeria

References

1.Aimiuwu, Victor O. (1992). Evaporative cooling of water in hot arid regions. Energy Convers. Mgmt Vol. 33, No. 1, pp. 69-74.

2.Aimiuwu, Victor O. (2008). An energy-saving ceramic cooler for hot arid regions (2008). Proceedings of the national society of black physicists..

3.Barry, C. S., & Giovannoni, J. J. (2007). Ethylene and fruit ripening. Journal of Plant Growth Regulation, 26(2), 143-159

4.Chaurasia, P. B. L., Singh, H., & Prasad, R. N. (2005). Passive cool chamber for preservation of fresh vegetables. SESI Journal : Journal of the Solar Energy Society of India, 15(1), 47-57.

5.Date, A.W. (2012). Heat and Mass transfer Analysis of clay-pot refridgerator. International Journal of Heat and Mass Transfer 55 (2012) 3977–3983

6.Evaporative cooling. (2003). Appropriate Technology, 30(3), 64-67. Retrieved from http://search.proquest.com/docview/200022214?accountid=11233

7.Mittal, A., Kataria, T., Das, G. K., & Chatterjee, S. G. (2006). Evaporative cooling of water in a small vessel under varying ambient humidity. International Journal of Green Energy, 3(4), 347-368.

8.Odesola, I., and Onyebuchi, O. (2009). A review of porous evaporative cooling for the preservation of fruits and vegetables. The Pacific Journal of Science and Technology, 10 (2), 935-941.

9.Tomoda, Shizue. "Recent Developments in the Food and Drink Industries." International Labour Review 131.4 (1992): 431-.