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Open Access Publications from the University of California

Scholarly Works (7 results)

  • Article
  • Peer Reviewed
UC Davis Previously Published Works (2023)
A stockpile heated and ambient air dryer (SHAD) was developed as an alternative to conventional almond windrow drying. Previous experiments showe that the drying air produced by SHAD was undesirably distributed through the almond stockpile. Therefore, an air distributor was developed containing 12 outlets, arranged in 4 rows of 3 outlets each. This study describes the comprehensive process of the air distributor design, manufacturing, and its optimization. The optimization process employed both computational fluid dynamics simulations and in-field airflow validation measurements. Initial 4-row air distributor in-field validation measurements indicated airflow distribution percentages were 4.1%, 30.8%, 44.9%, and 20.2% for the outlets in rows 1 through 4. This showed that almonds located around row 1 would not receive sufficient air to properly dry. Thus, an optimized 3-row air distributor configuration was developed and validated to yield an airflow distribution percentage of 31.3%, 44.4%, and 24.3% for outlets in the second to fourth rows, respectively. The 3-row air distributor configuration is therefore desirable, as the middle and tallest section of the stockpile will receive the highest airflow. The air distributor therefore markedly enhanced the SHAD's air supply distribution.
    Creative Commons 'BY' version 4.0 license
    • Thesis
    • Peer Reviewed
    UC Davis Electronic Theses and Dissertations (2021)

    Pest and human pathogen infestation, irrigation management, and visible dust generation during conventional almond harvesting challenge current harvest practices. Early, off-ground harvesting is a potential solution. However, almonds harvested early contain high moisture, making them susceptible to postharvest quality deterioration if not properly dried. Thus, this research proposes stockpile drying of almonds as an alternative. Stockpile drying eliminates sweeping and picking processes of conventional windrow drying, which emit significant dust. It reduces pest and human pathogen infestation by permitting early harvesting, and doesn’t interfere with irrigation timing, since it is not conducted in the almond orchard. A stockpile of 4,155 kg was dehydrated with a Stockpile Heated and Ambient air Dryer (SHAD), which uses a combination of heated and ambient air to achieve dehydration. Almonds were dehydrated for 11 days from an average dry basis moisture content (MCdb) equal to 12.6 % to a desired storage MCdb of around 6 %. However, there was non-uniformity of moisture observed throughout the stockpile attributed to the inability of the SHAD to properly distribute and deliver the drying air to the almonds. To address this, an air distributor containing 12 outlets, arranged in 4 rows with 3 outlets each was developed to enhance air distribution in the stockpile. The effect of using an air distributor as an additional component of the SHAD was evaluated with ‘Nonpareil’(Np), ‘Winter’(Wi), and ‘Monterey’(Mo) varieties of stockpile weight equal to 4,763 kg, 2,585 kg, and 6,849 kg, respectively. All experiments were directly compared with conventional windrow drying. Drying of almonds with a combination of SHAD and air distributor achieved desirable MCdb (< 6 %) across all varieties in a shorter time (maximum of 7 days), compared to the previous experiment without an air distributor (11 days). On the other hand, the conventional windrow drying took longer with drying periods (up to 13.63 days), and the desired final MCdb was only reached during the ‘Mo’ experiment. Further, the addition of the air distributor improved the specific moisture extraction rate, moisture extraction rate, and coefficient of performance by a percentage increase of 125%, 249%, and 255%, respectively. Thus, the SHAD with an air distributor can be used to directly dehydrate almonds outdoors in stockpiles and can replace conventional windrow drying of almonds.

      Cover page: Stockpile Drying Of Freshly Harvested Almonds
      • Article
      • Peer Reviewed
      UC Davis Previously Published Works (2023)
      An almond stockpile heated and ambient air dryer (SHAD) without an air distributor, did not adequately distribute air throughout the stockpile. Therefore, this project evaluated the effect of adding an air distributor within the SHAD A-frame as an alternative method to conventional windrow drying. Three stockpile drying tests were performed using ‘Nonpareil’, ‘Winter’, and ‘Monterey’ almond varieties with different initial (fresh) weights and kernel dry-basis moisture contents (MC) equal to 4763 kg and 11.8%, 2585 kg, and 11.5%, and 6849 kg and 21.5%, respectively. All tests were directly compared to conventional windrow drying. Almond quality parameters, including kernel MC, color, lipid oxidative stability, peroxide value, free fatty acid content, internal cavities, and insect injury were measured before and after drying. The SHAD with the air distributor properly maintained almond quality, while uniformly dehydrating almonds to the desired MC of ≤6 % within 7 days. Conventional windrow drying took up to 13.6 days, and the desired final MC was only achieved with the ‘Monterey’ variety. Thus, the SHAD fitted with a well-designed air distributor can be used to dehydrate almonds in a stockpile as an alternative to conventional windrow drying.
        Cover page: Drying of freshly harvested almonds using a stockpile heated and ambient air dryer (SHAD) with an air distributor -part 2
        • Article
        • Peer Reviewed
        UC Davis Previously Published Works (2021)
        Dust generated by farming activities is a safety hazard to farmworkers and an environmental contaminant. During the almond (Prunus dulcis) harvest in California, dust is primarily generated by the mechanized movement of almonds disturbing the bare soil of the orchard floor, during the sun-drying, windrowing process, and as they are transferred into trucks for transport to processing facilities. Off-ground dust-less harvesting will only be achieved when the almond industry adopts feasible mechanical drying methods. Therefore, a stockpile heated and ambient air dryer (SHAD) was developed to determine the feasibility of dehydrating almonds (Var. ‘Monterey’). A stockpile containing 4,155 kg of almonds was created and almonds were dehydrated from their initial 12.6% almond kernel dry-basis moisture content (MCdb) to final MCdb of 6.04%. Drying was achieved as a combination of heated air at a temperature of 55°C in the drying plenum with airflow of 0.078 m3/s per m3 of fresh almonds. After drying, almond quality parameters were measured, including damage by molds or decay, insect injury, and presence of internal cavities. Drying energy consumption, cost, and performance indicators were also determined. The differences in MCdb between the bottom, middle, and top layers of the almond stockpile were significant (p ≤ 0.05). Post-hoc Tuckey test was conducted which indicated that the MCdb in the top layer was significantly lower than almond MCdb in the middle and bottom layers. Results showed that damage by molds or decay, insect injury, and internal cavities were 1.81%, 0%, and 1.77%, respectively, after drying. Therefore, the overall almond quality was not compromised. The drying process cost $11.65 per tonne of the initial weight of almonds with a Specific Moisture Extraction Rate (SMER) of 0.64 kg/kWh, Moisture Extraction Rate (MER) of 1.02 kg/h, and a Coefficient of Performance (COP) of 1.33. Comparison with other dryers in the literature shows that SMER and MER were within limits. However, a low COP was observed.
          Creative Commons 'BY' version 4.0 license
          • Article
          • Peer Reviewed
          UC Davis Previously Published Works (2024)
          This study utilizes differential scanning calorimetry and thermogravimetric analysis to assess the total energy required to regenerate saturated zeolite-based drying beads (DBs) used to dry paddy rice. We quantify the required heat energy for DB regeneration by calculating the area under the curve in a heat flow rate versus time graph, with the end of the regeneration process indicated by stabilization of the DB weight. Our findings suggest that at DB regeneration temperatures ranging from 120 to 350 °C, the process varied from 813 to 22 min, demonstrating that higher temperatures lead to faster regeneration speeds. The total energy used for regeneration showed similar values at 250 and 350 °C, averaging around 2032 and 2136 kJ per kg of dried DB, respectively. Additionally, the study showed that DBs can hold water between 28.7% and 54.4% higher than the manufacturers specifications, suggesting a reduced quantity of DBs required for effective paddy rice drying. The overall required heat energy for the regeneration process was calculated at 4.86 MJ/kg, with a carbon intensity of approximately 275.61 g of CO2-eq per kg of water removed, resulting in lower values compared to conventional drying methods. The study underscores DBs possibility of lower total energy (thermal and electrical) consumption and greenhouse gas emissions, alongside its flexibility to regenerate with intermittent energy sources.
            Cover page: Energy Performance of Zeolite-Based Drying Bead Desiccants Used to Dry Paddy Rice.
            • Article
            • Peer Reviewed
            UC Davis Previously Published Works (2024)
            Coffee professionals have long known that the roast profile, i.e., the temperature versus time inside the roaster, strongly affects the flavor and quality of the coffee. A particularly important attribute of brewed coffee is the perceived sourness, which is known to be strongly correlated to the total titratable acidity (TA). Most prior work has focused on laboratory-scale roasters with little control over the roast profile, so the relationship between roast profile in a commercial-scale roaster and the corresponding development of TA to date remains unclear. Here we investigate roast profiles of the same total duration but very different dynamics inside a 5-kg commercial drum roaster, and we show that the TA invariably peaks during first crack and then decays to its original value by second crack. Although the dynamics of the TA development varied with roast profile, the peak TA surprisingly exhibited almost no statistically significant differences among roast profiles. Our results provide insight on how to manipulate and achieve desired sourness during roasting.
              Cover page: The effect of roast profiles on the dynamics of titratable acidity during coffee roasting.Creative Commons 'BY' version 4.0 license
              • Article
              • Peer Reviewed
              UC Davis Previously Published Works (2019)
              It has been estimated that one-third of global food is lost or wasted, entailing significant environmental, economic, and social costs. The scale and impact of food loss and waste (FLW) has attracted significant interest across sectors, leading to a relatively recent proliferation of publications. This article synthesizes existing knowledge in the literature with a focus on FLW measurement, drivers, and solutions. We apply the widely adopted DPSIR (Driver-Pressure-State-Impact-Response) framework to structure the review. Key takeaways include the following: Existing definitions of FLW are inconsistent and incomplete, significant data gaps remain (by food type, stage of supply chain, and region, especially for developing countries), FLW solutions focus more on proximate causes rather than larger systemic drivers, and effective responses to FLW will require complementary approaches and robust evaluation.
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