Evaluating passive evaporative cooling blanket for improved postharvest storage of fruit and vegetables in low- and middle-income countries

Abstract

Over 30% of fruit and vegetables produced in low- and middle-income countries is lost from farm to consumer. To combat this, cooling fresh produce after harvest is vital. Evaporative passive cooling is a viable solution, yet it is underutilized mainly due to complexity, scalability, and affordability issues for smallholder farmers. The passive cooling blanket represents a cleaner alternative to current evaporative coolers that can address these challenges. It is a re-usable textile-based blanket filled with a natural padding material such as sawdust or charcoal. However, its performance in real-world conditions has not been tested so far. This study evaluated the efficacy of two cooling blankets with capacities of 0.06 m³ and 0.18 m³ to preserve fresh produce by full-scale outdoor experiments in Kenya. Storage trials on tomato, kale, zucchini, and peas were conducted, comparing the blanket with a traditional charcoal cooler and storage under permanent shade. The blanket effectively lowered air temperature by 3–5°C below ambient, with a maximum reduction of 10°C during the warmest time of the day. It maintained a constant interior relative humidity of 95%, which slowed down the wilting of the produce. The cooling efficiency was 70% during the daytime. The blanket performed equally well or was slightly better than the traditional large charcoal cooler room in terms of humidity. The quality preservation of the vegetables was improved significantly compared to storage under the shade, reducing postharvest losses by up to 45%. The combination of cool temperatures and elevated humidity makes this storage method interesting for preserving several fruits or vegetables. A comprehensive cost analysis indicated that the payback period of the blanket is less than three months. Moreover, a survey among smallholder farmers and fruit vendors revealed an extremely high willingness to adopt this blanket. As a result, the passive cooling blanket emerged as a promising and sustainable solution for addressing postharvest storage challenges in low- and middle-income countries.