Open Drying Research Articles

Investigation on the effect of operation of solar dryer technology according to the drying characteristic of dried product

The application of solar dryer through greenhouse (GH) model as drying method for crops-based product is extremely important in industrial scale agriculture, especially in developed country. The drying model is considered environmentally friendly since it utilizes solar power as the main drying energy. However, the fundamental operational aspect of the basic GH is less discussed according to the drying mechanism of the dried product. In this work, three small-scale drying model are evaluated: open drying (OD), natural convection GH (NCGH), and forced convection GH (FCGH). The drying product is potato, which can be taken as an essential agricultural product in modern world. The OD model has the lowest mass loss rate which less than 50 % of the water from product can be evaporated. The operation of both GH is satisfactory, resulting more than 60 % moisture evaporation. The drying characteristic indicates the two-step failing rate which makes the mass loss fluctuation from the process. The highest mass loss is observed during the constant rate period around 21 % for FCGH and 18 % for NCGH. In addition, the detailed analysis on the effect of each process is discussed in this work. For example, the presence of hair-like structure and the movement of the pith of dried potato during the process. Also, a higher drying rate from NCGH and FCGH initiate the gelatinization and compartmentalization, resulting a substantial water evaporation of the product. It confirms the important correlation of the drying process and water diffusion mechanism of the dried product. The finding from this study can be taken as a vital reference for improving the operation of GH solar dryer

Effects of Different Natural Drying Methods on Drying Characteristics and Quality of Diaogan apricots

Drying is one of the best methods to preserve the quality of fresh fruits and prolong their shelf life. This study focuses on Prunus armeniaca L. cv. ‘Diaogan’ (commonly known as Diaogan apricot) sourced from Xinjiang, China to explore the impact of two natural drying methods (shade drying and open-air drying in the rocky desert) on the drying kinetics, color, textural characteristics, microstructure, chemical properties, and antioxidant capacity of Diaogan apricots. The experimental results indicate that throughout the natural drying process, the time required for open-air drying in the rocky desert was reduced by 26.47% compared to shade drying. The L*, a*, and b* values of the shade- and ventilation-dried Diaogan apricots were higher than those sun-dried in the rocky desert, exhibiting a lower color difference (ΔE) than apricots dried through rocky desert sun drying. Specifically, the ΔE for shade-dried Diaogan apricots was 19.66 ± 0.24. The Diaogan apricots dried in the rocky desert exhibited greater hardness, lower elasticity, stronger adhesiveness, and higher chewiness compared to those dried in the shade, with the hardness, adhesiveness, and chewiness being, respectively, 14.71%, 18.89%, and 35.79% higher. Scanning electron microscopy (SEM) observations revealed that the high temperatures experienced during open-air drying in the rocky desert caused rapid dehydration of the Diaogan apricot’s skin, leading to clogging and crust formation in the flesh pores, along with deformation or tearing of the tissue structure, ultimately resulting in poor rehydration ability. After drying, there was a significant increase in the soluble solids in the Diaogan apricots, whereas titratable acidity, total phenols, ascorbic acid, and antioxidant capacity were significantly decreased (p < 0.05). In summary, the quality of dried Diaogan apricots post-drying is dependent on the natural drying method employed, with shade drying resulting in superior quality of Diaogan apricots compared to open-air drying in the rocky desert. This study offers fundamental data and serves as a theoretical reference for the industrialized production of apricots.

The Mathematical Modeling, Diffusivity, Energy, and Enviro-Economic Analysis (MD3E) of an Automatic Solar Dryer for Drying Date Fruits

Date fruit drying is a process that consumes a significant amount of energy due to the long duration required for drying. To better understand how moisture flows through the fruit during drying and to speed up this process, drying studies must be conducted in conjunction with mathematical modeling, energy analysis, and environmental economic analysis. In this study, twelve thin-layer mathematical models were designed utilizing experimental data for three different date fruit varieties (Sakkoti, Malkabii, and Gondaila) and two solar drying systems (automated solar dryer and open-air dryer). These models were then validated using statistical analysis. The drying period for the date fruit varieties varied between 9 and 10 days for the automated solar dryer and 14 to 15 days for open-air drying. The moisture diffusivity coefficient values, determined using Fick’s second law of diffusion model, ranged from 7.14 × 10−12 m2/s to 2.17 × 10−11 m2/s. Among the twelve thin-layer mathematical models, we chose the best thin drying model based on a higher R2 and lower χ2 and RMSE. The Two-term and Modified Page III models delivered the best moisture ratio projections for date fruit dried in an open-air dryer. For date fruit dried in an automated solar dryer, the Two-term Exponential, Newton (Lewis), Approximation diffusion or Diffusion Method, and Two-term Exponential modeling provided the best moisture ratio projections. The energy and environmental study found that the particular amount of energy used varied from 17.936 to 22.746 kWh/kg, the energy payback time was 7.54 to 7.71 years, and the net CO2 mitigation throughout the lifespan ranged from 8.55 to 8.80 tons. Furthermore, economic research showed that the automated solar dryer’s payback period would be 2.476 years.

Comparative evaluation of drying methods for struvite produced from electrocoagulated source-separated urine: Implications for quality, energy and cost-effectiveness

Struvite precipitation from source-separated urine is crucial for waste utilization and sustainability. However, after precipitation, the high moisture content of struvite necessitates an additional drying process that can be costly and inefficient. In the present study, the performance of different drying methods—open sun drying, air drying, conventional drying (20–100 °C), and microwave drying (180–720 W) on the quality of struvite obtained from source-separated urine through electrocoagulation using Mg–Mg electrodes were evaluated. It was found that higher temperatures and power in the convective oven and microwave resulted in higher diffusivity (10−9-10−7 m2s−1), leading to reduced drying times. Different models were employed to comprehend the drying mechanism, and the one with the highest correlation coefficient (R2 = 0.99) and the lowest statistical values was selected. The key findings indicated that higher power and temperature levels were more cost-effective. However, characterization of the dried struvite using X-ray diffraction and Fourier-transformed infrared spectroscopy, disintegration of struvite crystals at temperatures above 60 °C in the conventional oven and 180 W in the microwave oven was observed. Based on the results, we conclude that sun drying is a cost-effective and environmentally friendly alternative for drying struvite without compromising its quality.

Some Quality and Microbiological Traits of Tokat Tarhana Obtained from Different Wheat Cultivars Under Various Drying Conditions

This study was carried out to evaluate the variations in some quality traits of Tokat red pepper tarhana samples according to the cultivars and drying techniques. For this aim, five white grained bread wheat cultivars such as Altınöz, Candaş, Gökkan, Şahika, and Yakamoz were used as material. And, tarhana samples were dried under open air, airflow oven and vacuum. The study was conducted with three replications according to the split plot design in random plots. All quality traits showed statistically significant variations for the bread wheat cultivars (C), drying techniques (DT), and DT×C interactions. Thus, airflow oven showed the highest values among the drying techniques for the contents of ash (8.5892%), total titration acidity (27.433%) and salt (6.842%). On the other hand, open air drying technique presented the highest values for moisture (14.556%), pH (4.349) and the density of lactic acid bacteria (LAB) (1.4×104 CFU g-1 for M17 agar, 2.4×104 CFU g-1 for MRS agar. Also, Gökkan cv had the highest percents for all quality traits except LAB density. These findings showed that the most suitable bread wheat cultivar for Tokat red pepper tarhana was Gökkan cv, and the most favorable drying technique was open air drying. In addition, it is understood from the results that wheat cultivar and drying technique which used in tarhana production were essential factors. So, tarhana sector should choose the best wheat cultivar and drying technique to be used in tarhana production for consumer taste and healthy diet. From this study, it is understood that the open air drying is the most sustainable technique in terms of both production and consumption.

IoT for Monitoring Fungal Growth and Ochratoxin A Development in Grapes Solar Drying in Tunnel and in Open Air.

Optimisation of solar drying to reduce fungal growth and Ochratoxin A (OTA) contamination is a crucial concern in raisin and currant production. Stochastic and deterministic analysis has been utilized to investigate environmental indicators and drying characteristics. The analysis was performed using two seedless grape varieties (Crimson-red and Thompson-white) that were artificially inoculated with Aspergillus carbonarius during open-air and tunnel drying. Air temperature (T) and relative humidity (RH) were measured and analysed during the drying experiment, along with grape surface temperature (Ts), and water activity (aw). The grape moisture content, fungal colonization, and OTA contamination were estimated, along with the water diffusivity (Deff) and peel resistance (rpeel) to water transfer. Monitoring the surface temperature of grapes is essential in the early detection of fungal growth and OTA contamination. As surface temperature should be carried out continuously, remote sensing protocols, such as infrared sensors, provide the most efficient means to achieve this. Furthermore, data collection and analysis could be conducted through the Internet of Things (IoT), thereby enabling effortless accessibility. The average Ts of the grapes was 6.5% higher in the tunnel than in the open-air drying. The difference between the RH of air and that in the plastic crates was 16.26-17.22%. In terms of CFU/mL, comparison between white and red grapes in the 2020 and 2021 experiments showed that the red grapes exhibited significantly higher values than the white grapes. Specifically, the values for red grapes were 4.3 in 2021 to 3.4 times in 2020 higher compared to the white grapes. On the basis of the conducted analysis, it was concluded that tunnel drying provided some advantages over open-air drying, provided that hygienic and managerial requirements are met.

Design and Implementation of a PV-Integrated Solar Dryer Based on Internet of Things and Date Fruit Quality Monitoring and Control

In Egypt, the climate has a direct impact on the dried date fruit production. The traditional drying method or open sun drying (OSD) leads to pollution of the final product caused by sand-laden winds, rain, or animals and harmful insects, etc. This study is aimed at designing, implementing, and experimentally validating a solar dryer based on IoT technology and integrated with a PV system in Aswan, Egypt. The purpose of the dryer is to monitor and control the quality of the three most popular date fruit varieties and determine the most effective drying method, with an algorithm that operates the system automatically for optimal performance and high-quality products. The automatic solar dryer (ASD) significantly affects the final moisture content and color characteristics and reaches the equilibrium moisture content (EMC) at a faster rate for dried date samples compared to the OSD. The drying rate of ASD was 29.03% (Sakkoti), 31.04% (Malkabi), and 25.49% (Gondaila) higher than OSD. Also, the dried date fruit samples reached EMC on the ASD after 8 days for both Malkabi and Gondaila and 9 days for Sakkoti, while it took 14 to 15 days on OSD. The maximum open circuit voltage V oc , short circuit current I sc , and output power P output were 41.70 V, 8.84 A, and 365.09 W, respectively. All values of total color change ( Δ E ∗ ) after open-air drying of dry date varieties were higher than solar drying for both drying systems. This study can be then more helpful for producers of dried foods.

Technical performance and economic efficiency of small-scale maize dryers in Kenya

Maize is the most important cereal in East and Southern Africa, but its production is highly seasonal. Maize storage is therefore essential for food security, and so is drying before storage, typically to 13.5%. New small-scale dryers have been proposed but their performance has not been tested. The technical performance and economic efficiency of small maize dryers were therefore assessed during two on-station experiments conducted after the main harvest of 2021 in Njoro, Kenya (1800 masl, temperature 17–22 °C). Six available dryers were tested: EasyDry (capacity 495 kg, cost of KES 85k), the green house (180 kg, KES 33k), the Multipurpose (90 kg, KES 30k), the POD (90 kg, KES 15k), the Dehytray (7 kg, KES 6k) and the Hybrid (5 kg, KES 17k), and compared to open-air drying (180 kg, KES 5k). In their technical performance, all dryers were faster than open-air drying, which took on average 21.1 h to dry one batch of maize (2.4 h/% point), but only one dryer, EasyDry M500, was substantially faster (8.6 h or 1.03 h/%), as it uses maize cobs for fuel, followed by Dehytray (15.6 h); other dryers took much longer (between 17.6 and 19.9 h). As per the economic analysis, open-air drying was the cheapest drying method, at 0.4 KES/kg maize (US$ 4/tonne). The cost of solar drying strongly decreased with the dryers' capacity, with a cost of 1.4–1.8 KES/kg for the cheapest. Small dryers (<10 kg) were prohibitively expensive and not profitable for routine drying of maize. In conclusion, the dryers tested were economically not competitive with open air drying of maize as they are more expensive, unless other factors are considered, in particular the high drying rate of the EasyDry M500, and the better grain quality of closed systems such as Greenhouse and POD dryers.

Valorization potential of dried tannery fleshing wastes (TFW) through pyrolysis in the leather industry: Kinetic and thermodynamic investigations

Since the moisture content of the tannery fleshing waste (TFW) of the leather industry is too high, this paper evaluates the effects of open air and greenhouse drying pretreatment on the valorization potential of these wastes by pyrolysis. The pyrolysis behavior and kinetics were studied using KAS and Starink model-free methods and the reaction mechanisms of both dried TFW samples were established by the Coats-Redfern model. The activation energy (Eα) calculated by KAS and Starink methods were similar for both samples, resulting in 121.71, 149.32 and 169.80 kJ mol−1 for TFW-OD and 155.41, 203.33 and 175.19 kJ mol−1 for TFW-GD in the first, second and third stages respectively. Moreover, the performance of two drying approaches on the behavior of TFW slow pyrolysis was studied at 500 °C and focused on biochar production to improve the feasibility of the TFW pyrolysis process, with the main goal of moving towards circular economy in the leather industry. The obtained results revealed that produced biochars are not suitable for either subsequent energetic valorization as fuels (H/C > 0.7). However, they showed a great potential for soil amendment (R50 = 0.11–0.12), long-term carbon storage (O/C < 0.4), fertilizers or sorbent for tannery wastewater treatment where adsorption of dyes is essential. Amongst the drying pretreatments, the open-air drying method proved to be the most suitable for industrial scale unit to convert TFW into economic value biochar.

Response surface optimization and social impact evaluation of Houttuynia cordata Thunb solar drying technology for community enterprise in Chiangrai, Thailand

Drying has emerged as one of the most important ways of preserving high-quality and quantity food goods. A force convection solar drying is considered an ecologically and environmentally friendly alternative. This research presents parameter optimization of greenhouse tunnel dryer of Houttuynia cordata Thunb (H. cordata) using response surface methodology with the assessment of economic feasibility and social return on invesment. The influence parameters of the drying process were evaluated to obtain maximum efficiency. The individual parameters were temperature (40 – 60 °C), material length (10 – 30 cm), and relative humidity (30 – 50%). The individual parameters of drying temperature showed an extreme effect on the response of moisture content and color value change, while the relative humidity had only an influence on moisture content. On the other hand, the parameter of material length was not significance in both responses. When compared to open-air drying, solar drying reduced the drying time of H. cordata by 57.14%. The payback period of the dryer was found to be 2.5 years. Furthermore, the results reveal that the social return on investment ratio in 2021 was 2.18, then increasing to 2.52 in 2022 and 2.91 in 2023. According to the findings, solar drying technology has the potential to be an adequate product quality improvement technology for H. cordata. It is a feasible drying technology in terms of economic evaluation.

Experimental performance analysis of a mixed forced convection solar dryer: Application to cocoa bean drying

The influence of a mixed forced convection solar dryer with thermal storage, on the quality of cocoa beans is studied. This study has as reference the quality level recommended by the international standard ISO 2451. A collection of experimental data with the realized dryer was made for six days on a sample of 10 kg of cocoa coming from the cocoa zone of Kekem in Cameroon. This sample consisted of more than 300 cocoa beans as recommended by the standard for testing. The dryer, is mainly made of wood for the frame and polystyrene for the isolating part, it has an operation based on a combination of the direct and indirect model. A control and measuring device for airflow, temperature and humidity has been installed in the drying chamber. The dryer's direct solar component can be used to accelerate the drying process, especially during the first drying phase. This experimental system was able to dehydrate cocoa beans in 2 days with a water content that went from 53.4 % to 4.6 %. From the beginning to the end of the drying process, the temperature and the relative humidity were respectively between 18 and 55 °C and between 28 and 80 %. Placing the same amount of beans in the acceleration chamber, the drying chamber and in the open air, for an amount of water to be removed of about 5.07 kg, the water removal rates were respectively about 0.32 kg/h, 0.21 kg/h and 0.10 kg/h for an effective daily average of 8 h. The drying performances of the acceleration chamber and the drying chamber are respectively 68 % and 52 %, more than the open-air drying.

Novel Method of Increased Efficiency Corn Drying on a Fixed Bed by Condensation

Exhaust air recycling is a simple and commonly used technique to save energy when using a dryer. The fixed-bed drying test device with increased efficiency by condensation is a clean and energy-saving drying test device developed by combining exhaust air recycling and condensation dehumidification technology. In this paper, through comparisons with or without exhaust air circulation using the single factor test of drying process parameters and the response surface test of corn drying on this test device to investigate the energy-saving effect and drying characteristics resulting from the novel drying method of increased efficiency by condensation. We drew the following main conclusions: (1) increased efficiency drying by condensation resulted in an energy savings of 32-56% compared with the conventional open hot air drying; and (2) during the increased efficiency corn drying by condensation, the mean energy and exergy efficiencies were within 31.65-51.26% and 41.69-63.52%, respectively, when the air temperature was in the 30-55 °C range, and they were 24.96-65.28% and 30.40-84.90%, respectively, when the air passed through the grain layer at 0.2-0.6 m/s; both of these increased with increasing air temperature, and decreased with increasing air velocity. These conclusions may constitute an important reference for investigating the energy-saving drying process of increased efficiency by condensation and developing relevant energy-saving drying equipment.

Energy efficient drying technologies for sweet potatoes: Operating and drying mechanism, quality-related attributes.

Sweet potatoes (SPs) are a versatile tuberous crop used as subsistence and cash crop in raw and processed forms. The major issue with SPs is post-harvest losses, which result in noticeable quality decline because of inappropriate handling, storage, delayed transit, and sales, as well as microbiological and enzymatic activity. Drying is an excellent strategy for managing short postharvest storage life, preserving nutrients, and maximizing long-term benefits. However, several parameters must be considered before drying SPs, such as relative humidity, temperature, drying duration, size, and shape. The current review looks at the factors influencing SPs' moisture loss, drying kinetics, diverse drying methods, pretreatments, operating conditions, and their efficacy in improving the drying process, functional, and nutritional qualities. An optimal drying process is required to preserve SPs to obtain concentrated nutrients and improve energy efficiency to be ecofriendly. Drying sweet potatoes using traditional methods such as sun or open-air drying was found to be a slow process that could result in a lower quality. Various advanced drying techniques, like vacuum, infrared, freeze drying, and pretreatments such as ultrasound and osmotic dehydration, have been developed and are successfully used globally. The best-fit thin-layer models (Hii, Page, two-term, logarithmic) utilized for drying SPs and appropriate modeling methods for optimizing drying procedures are also discussed.

EVALUATION OF THE QUALITY CHARACTERISTICS OF COCOA BEAN DRIED USING DIFFERENT DRYING TECHNIQUES

Processing techniques, particularly drying because cocoa beans are extremely sensitive to moisture, have a significant impact on the quality of the final product. Fermented cocoa beans were dried using the NSPRI parabolic solar tent dryer (PSTD), wooden solar dryer (WSD), and open-air drying (OAD). The dried cocoa beans’ respective moisture contents (MCs) for PSTD, WSD, and OAD were 5.94%, 6.01%, and 6.82%, respectively. The corresponding MCs for the dried cocoa beans from PSTD, WSD, and OAD were 5.94%, 6.01%, and 6.82, respectively. It was found that the cut test scores for PSTD, WSD, and OAD were 1000, 985, and 965, respectively. This showed that, in contrast to those from WSD and OAD, the dried cocoa beans obtained from PSTD were fully brown. For WSD, OAD, and PSTD, respectively, the obtained pH values were 5.60, 5.65, and 5.80, and the total titratable acidity was 11.70 meq NaOH 100–1 g, 14.10 meq NaOH 100–1 g, and 18.30 meq NaOH 100–1 g for PSTD, WSD, and OAD, respectively. Food products’ shelf life may be indicated by the titratable acidity value. Due to its enclosed design, the NSPRI PSTD has an advantage over other drying methods because it completely eliminates the possibility of external and microbial contamination of the cocoa beans.

"COMPARATIVE STUDY OF DRYING CHARACTERISTICS OF AMLA FRUIT USING OPEN SUN DRYING AND SOLAR DRYING METHOD"

Amla fruits were utilised in this study to compare solar drying with open sun drying. For drying, open sun drying was used, and a lab-scale solar dryer was also constructed. Drying temperature, moisture content (MC), and drying rate were the comparison criteria used. In order to com pare solar drying of amla with natural sun drying, three different air velocity flow rates are used: 5 m/s, 5.5 m/s, and 6 m/s. The ambient temperature is between 25ºC and 35ºC, while the drying chamber's temperature ranges from 50 to 85 degrees Celsius. The proposed dryer's efficiency ranges fro m 36.56 to 48.45 percent, whereas sun drying's efficiency ranges from 11.4 to 16.64 percent. It has been found that as air velocity flow rates rise, the dryer's efficiency rises as well. In identical environmental conditions, the solar dryer dried clothes more quickly than open-air drying. Compared to sun drying, which takes 12–16 hours, solar drying takes 4–8 hours to attain a safe moisture content. Additionally, the value of solar dried amla is superior to that of sun dried amla in terms of colour, flavour, odour, and look. The current work's observed results demonstrate that the suggested solar dryer works well for drying amla in this area.

Reduction of aflatoxin in freshly harvested maize using solar dryers.

Aflatoxin-contaminated grain consumption over the years has been known to result in serious health hazards for its consumers. The present study investigated the effects of harvest seasons and drying methods on aflatoxins in freshly harvested maize. A 2 × 3 × 3 × 3 × 3 factorial design was used; two harvesting seasons (dry and wet), maize varieties (P3966W, P4063W and P4226), moisture contents (0.15, 0.12, and 0.10 g kg-1 ), modern fabricated solar dryer (MFSD), hybrid biomass dryer (HBD) and open-air drying (OAD) methods, and packaging materials (plastic, jute and polyethylene bag) were studied, respectively. In total, 162 samples (n=162) of maize grains (250 g each) were dried. The freshly harvested maize was shelled, dried, stored and analyzed for aflatoxins using high-performance liquid chromatography. The data obtained were subjected to statistical analysis. P3966W and P4063W with an initial moisture content of (0.226 and 0.234 g kg-1 ) reached a safe level of 0.10g kg-1 using MFSD within 2-3 days, HBD within 2-3 days and OAD within 5 days. Variety P4226 with an initial moisture content of 0.228 g kg-1 reached a safe moisture level of 0.10g kg-1 in 2, 3, and 7 days using MFSD, HBD and OAD, respectively. Aflatoxin concentration (56.00 ± 8.89 μg kg-1 ) was highest in P4063W at 0.15 g kg-1 moisture content, which exceeded the maximum permissible limits of 4 μg kg-1 recommended by the World Health Organization. Variety, type of dryer and season affect aflatoxin contamination of maize. The adoption of MFSD drastically reduced the duration of drying and consequently controlled contamination by aflatoxins. © 2022 Society of Chemical Industry.

Preventive practices by households against Lassa fever transmission in Ondo State, Southwest, Nigeria

continued transmission of Lassa fever has been recorded in 6 Local Government Areas (LGAs) of Ondo State in Southwest, Nigeria annually with high case fatality rates. Genomic analysis of the Lassa virus has indicated ongoing transmission from local rodents´ population to humans despite several public health interventions during the outbreak including risk communication on preventive practices against the disease. We assessed adherence to preventive practices by household against the spread of Lassa fever in these affected LGAs. a descriptive cross-sectional study was conducted among community members in the six affected Local Government Area (LGAs). A semi structured questionnaire was administered to 2992 consenting respondents to assess their reported preventive practice against Lassa fever while their observed practices was assessed using observation checklist. Data analysis was done using frequency, proportions, Chi-Square test and logistic regression of predictors of outcome variable with statistical significance set at p<0.05. a higher proportion of the respondents were females (51.2%) compared to males (48.8%) with mean age of 43.04±13.97 years. Majority of the respondents (88.2%) were married with at least secondary education (76.7%). Majority of the respondents (80.2%) reported washing their hands with soap and water regularly, 84.6% washed their utensils before and after use likewise. However, 10.6% of the respondents reported not storing their food items in lid-covered containers while 61.9% practiced open air drying of food items by the roadside. Also, 34.3% of the respondents were observed to spread food items outside their home in the open air. Overall, 32.6% of the respondent were observed to have poor preventive practices against Lassa fever with their level of education as a significant determinant. the poor preventive practices observed among the respondents in this study could sustain the transmission of the virus hence there is also the need to further intensify enforcement of public health control measures for Lassa fever through existing community structures and institutions to stop the current and prevent future Lassa fever and other related outbreaks in the State.

Economics of open-air sun drying in the maize value chain of Kenya

In Africa maize is the main food staple and proper drying is crucial to contain storage losses. Open-air drying is the common practice, but new methods including solar and biomass-heated dryers are being proposed; therefore, their efficacy and profitability need to be compared to current practice. As traders can more easily estimate drying costs and maize prices than farmers, we estimated the efficacy, costs and benefits of open-air drying based on interviews with 122 traders in Kenya. Respondents reduced maize moisture content by 5.8% (from 17.8%), at a cost of KES 113/90 kg bag (US$ 1.13) or KES 22/90 kg bag/% moisture (US$ 2.46/tonne/% moisture or 0.7% of the grain value). The interviews also indicated that drying is an integral part of the larger maize trading and value chain. The rate of return (RoR) for transporting maize from purchase place to drying place, plus actual drying, was estimated at a modest 11%; The RoR of transporting maize from drying place to point of sale, on the other hand, was a strong 24%, while the overall RoR over the whole value chain was the highest, at 26%. We conclude that profits from maize drying itself are rather small, and that profits from trading in the maize value chain are largely derived from spatial arbitrage. Further, it needs to be ensured that alternative drying technologies are more economical than open-air drying, by comparing their performance to open-air drying using the parameters presented here. • 123 traders operating open-air sun drying of maize were interviewed in Kenya. • Traders reduced moisture by 5.8% at a cost of US$ 12.56/t or US$ 2.46/t/% moisture. • Rate of return for transport + drying was 11%, transport + sales 24%, overall 26%. • Drying is an integral part of the larger maize trading and value chain. • Maize drying profits are small, trading profits come mostly from spatial arbitrage.

Environmental Conditions Affecting Ochratoxin A during Solar Drying of Grapes: The Case of Tunnel and Open Air-Drying.

Drying optimization, to mitigate fungal growth and Ochratoxin A (OTA) contamination is a key topic for raisin and currant production. Specific indicators of environmental conditions and drying properties were analyzed using two seedless grape varieties (Crimson—red and Thompson—white), artificially inoculated with Aspergillus carbonarius under open air and tunnel drying. The air temperature (T), relative humidity, grape surface temperature (Ts) and water activity throughout the drying experiment, the grapes’ moisture content and the fungal colonization and OTA contamination during the drying process and their interactions were recorded and critically analyzed. Drying properties such as the water diffusivity (Deff) and peel resistance to water transfer were estimated. The grapes Ts was 5–7 °C higher in tunnel vs. open air–drying; the infected grapes had higher maximum Ts vs. the control (around 4–6 °C). OTA contamination was higher in tunnel vs. open air–dried grapes, but fungal colonies showed the opposite trend. The Deff was higher in tunnel than in the open air–drying by 54%; the infected grapes had more than 70% higher Deff than the control, differences explained by factors affecting the water transport. This study highlighted CFU and OTA indicators that affect the water availability between red and white grapes during open air and tunnel drying, estimated by the Deff and peel resistance. This raises new issues for future research.

Investigation on indirect solar dryer for drying sliced potatoes using phase change materials (PCM)

The solar dryers are playing a pivotal role in the food industries for preserving edible items such as grains, vegetables, fish, etc., through the removal of moisture content from them. They are having benefit over the open air drying by protecting the food items from dust, insects and other detrimental things. Further, they are attributed to save a greater amount of energy and protect the ecosphere from degradation. The indirect type solar dryers are primarily consisting of a solar collector and a space to place sliced potatoes. Their moisture removal rate is high and the quality of the end product would also be improved by them. In this present work, an indirect type single-pass forced convection solar dryer was fabricated and paraffin was integrated with solar collector as phase changing material (PCM) to improve the off-sunshine hour performance of the solar dryer. The process parameters such as, moisture removal rate, moisture ratio and the dryer inlet temperature were investigated for drying sliced potatoes in two cases, namely, solar dryer without PCM (Plain Dryer) and solar dryer with PCM (PCM Dryer). The mass flow rate of air was maintained as 0.065 kg/s and the dryer was operated from 10.00 a.m. to 7.00 p.m. The obtained results were compared and the influence of amalgamating PCM with the solar dryer was analyzed and presented. The results demonstrated that the presence of PCM within the solar collector enhanced the drying room temperature significantly, two more hours after solar period. In addition, the percentage weight of moisture removal from potato slices was enhanced by 5.1% per day with the aid of paraffin.