Franz Roman

The roasting process of Gari (Gelatinized cassava mash), a shelf-stable cassava product, is energy-intensive. Due to a lack of information on thermal characteristics and scarcity/rising energy costs, heat and mass transfer calculations are essential to optimizing the traditional gari procedure. The objective of this study was to determine the proximate, density, and thermal properties of traditionally processed de-watered cassava mash and gari at initial and final processing temperatures and moisture contents (MC_wb). The density and thermal properties were determined using proximate composition-based predictive empirical models. The cassava mash had thermal conductivity, density, specific heat capacity, and diffusivity of 0.34 to 0.35 W m⁻¹ °C⁻¹, 1207.72 to 1223.09 kg m⁻³, 2849.95 to 2883.17 J kg⁻¹ °C, and 9.62 × 10⁻⁸ to 9.76 × 10⁻⁸ m² s⁻¹, respectively, at fermentation temperatures and MC_wb of 34.82 to 35.89 °C and 47.81 to 49%, respectively. The thermal conductivity, density, specific heat capacity and diffusivity of gari, ranged from 0.27 to 0.31 W m⁻¹ °C⁻¹, 1490.07 to 1511.11 kg m⁻³, 1827.71 to 1882.61 J kg⁻¹ °C and 9.64 × 10⁻⁸ to 1.15 × 10⁻⁸ m² s⁻¹, respectively. Correlation of all the parameters was achieved, and the regression models developed showed good correlation to the published models developed based on measuring techniques.

A gombisa is a traditional Ethiopian structure widely used for maize storage over several months. It lacks adequate ventilation for timely moisture removal, which promotes mold development and aflatoxin production. In this study, a traditional gombisa was compared to one modified by installing a solar powered fan to provide forced ambient air ventilation during daytime. Approximately 900 kg of moist ear maize were loaded into each structure and samples from selected locations were weighed periodically to monitor moisture loss. Temperature and relative humidity of ambient air and inside the maize bulk were continuously recorded. Significantly faster drying was achieved in the modified gombisa, where drying occurred from bottom to top. In the traditional store, drying was much faster at the surface, with drying rate declining sharply with increasing depth in the bulk due to more limited air exchange. Relative humidity in the bulk center of the traditional structure remained above 90% for more than 4 weeks while in the modified gombisa it decreased progressively from the beginning of the trial. The results are promising and the modifications simple to implement, with the potential to effectively reduce post-harvest losses of maize. Field tests in Ethiopia are recommended.

Maize is an important foodstuff in many countries, and one of most susceptible crops to mold and aflatoxin contamination, which results in considerable postharvest losses and is a burden to consumers’ health, especially in developing countries. The timely drying of harvested maize is essential to halt mold development, ensuring safe storage. The effect of the incorporation of a superabsorbent polymer (SAP) as desiccant in a maize dryer was studied using computational fluid dynamics simulations which accounted for heat and mass transfer between maize, SAP and air. The adsorption capacity and adsorption rate of a commercial SAP material were experimentally determined at different temperature and relative humidity levels, which served as basis for the adsorption model required in the simulations. A maize bulk with SAP packages distributed in it was modeled. Results showed that the SAP material increases the drying rate substantially, particularly in the upper bulk zone where the air reaching it is dehumidified the most. The maize closer to the upper bulk surface starts drying from the beginning of the process instead of lagging for hours or days before the drying front reaches it. An inconvenience of the SAP material is the tendency of granules to swell and stick together as moisture reaches a threshold, which may reduce its performance. Thus, provided this issue is resolved or minimized, SAP materials could successfully assist the rapid drying of maize and other crops. They may also be used during storage to avoid rewetting of the crops during periods of high relative humidity.