Vegetable Cooling and Storage Evaluation

Background

MIT D-Lab, in partnership with the World Vegetable Center, conducted an evaluation of technologies designed to improve the storage of vegetables using evaporative cooling. The methodologies used included interviews with users of the cooling and storage technologies, interviews with stakeholders along the vegetable supply chain, and sensors to monitor product performance parameters. The study took place in Mali, where the World Vegetable Center is engaged in ongoing work with horticulture cooperatives and farmers. Suitable cooling and storage technologies have the potential to prevent food loss (thereby increasing access to nutritious foods), strengthen the perishable food supply chain, and create opportunities for additional income generation. Because these designs for cooling chambers work with the natural cooling processes of evaporation, they are well suited for regions where electricity is either not available or not affordable.

Results

The research team studied two different categories of vegetable cooling technologies: large-scale evaporative cooling chambers (ECCs) constructed from brick, straw, and sack suitable for farming cooperatives, and devices made from clay pots for individuals and small-scale farmers. Over time, they monitored changes in temperature and humidity inside the devices to understand when they were most effective. The evaluation results showed that the devices provide temperature decrease, increased humidity, and protection from pests, which resulted in significant increases in shelf life for commonly stored vegetables including tomatoes, cucumbers, eggplant, cabbage, and hot peppers. Users reported that this improved storage environment had positive impacts for users including reduced post-harvest losses, less time spent traveling to the market, monetary savings, and increased availability of vegetables for consumption. These devices can also have farther-reaching impacts, particularly on women, who often make pottery and could benefit economically from producing clay pots. The comparison of three ECC types demonstrates that ECCs made of brick are superior to ECCs made of straw or burlap sacks. Brick ECCs provide a more stable low temperature and high humidity environment, are easier to refill with water, and provide protection from animals and insects. Due to these considerations, straw and sack ECCs are not recommended. When comparing clay pot coolers, devices with a pot-in-pot configuration provide a greater temperature decrease than clay pot coolers with a pot-in-dish configuration. Both types of devices perform similarly on other metrics such as interior humidity, ease of watering, and protection from animals and insects. These results indicate relatively loose design constraints for constructing a clay pot cooler that provides a basic level of performance, even if not optimized, creating an opportunity to repurpose locally available materials and create an effective clay pot cooler for vegetable cooling and storage. Ninety percent of those interviewed reported that they were no longer using any of their previous storage methods after receiving the clay pot coolers, indicating that the 50 liter capacity of the clay pot coolers used in this study is sufficient to meet the vegetable storage needs of most households.

Practitioner Resources

However, evaporative cooling devices are not appropriate for all settings: they are best suited to communities where there is access to water and vegetable storage is needed during hot and dry weather. In addition to the evaluation report the research team has developed two practitioner tools: an interactive “Evaporative Cooling Decision Making Tool” and an “Evaporative Cooling Best Practices Guide” to support the determination of ECCs and clay pot cooler suitability and the devices’ proper construction and use. The intended audience for these resources includes government agencies, nongovernmental organizations, civil society organizations, and businesses that could produce, distribute, and/or promote ECCs or clay pot coolers.

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