Dryers: Refractance Window Dryer and other B2B products

This continues until a precise point of dehydration is reached, at which point the drying process automatically stops. Another innovation in food and feed drying technology is an “airless” dryer that uses superheated steam at atmospheric pressure rather than heated air as the drying medium. This product was developed by the Dupps Company, another major dryer manufacturer. According to Robert Horton, process engineer from Dupps, Refractance Window Dryer this dryer has about the same energy consumption as conventional direct-fired dryers. “However,” adds Horton, “The exhaust contains latent heat, which can be recovered.” He adds that the exhaust can be condensed and the water potentially reused in the process. An interesting innovation in food drying is the Refractance Window® concept introduced by MCD Technologies, a dryer manufacturer headquartered in Tacoma, Washington.
The walnut kernel drying is usually done by the sun-drying process in different units . Fresh walnuts were dried for 5 days under direct contact with the sun and every night the walnut kernels were collected back, this whole operation was finished in 5 days and the total drying time was 48 h. The final moisture content obtained was 5% . Traditionally hot air drying method is used for the drying purpose of walnuts in industries that have lower energy efficiency and more time is required for drying.

Computed results indicated that there was a 5% increase in transmission of IR radiation through the plastic sheet between a dry and wet product. A major portion of thermal energy was transferred via conduction through the plastic sheet. As a consequence, quality of the RW dried product is preserved when compared with other drying techniques (Monica Jimena Ortiz-Jerez, Gulati, Datta, & Ochoa-Martínez, 2015). The results obtained in this study depict that refractance window drying is a promising technology for drying walnuts and can be used as an efficient alternative to traditional sun drying. The ΔE value of kernels was found lowest (4.36) at 70 °C.
The dendrogram Fig.7 represents the compound correlation between all the treatments of refractive window drying and indicates that the sample dried at node 4 (80 °C) and node 5 (90 °C) have a similar pattern in all the studied parameters. A similar pattern can also be observed for the samples dried at 50–60 °C indicating a cluster of nodes 1 and node 2. The dendrogram distance for both clusters were about 100 with respect to 500 for all the cases. The total phenolic content was determined as per the method followed  by Amin et al. with minor modifications. The sample was mixed with 5 mL of 0.25 N Folin Ciocalteu reagent. After 3 min incubation at temperature 37 °C, 4 mL of 7.5% Na2CO3 was added to the mixture and incubated for 2 h at room temperature.
IC50 was calculated as per the method reported by Najmina et al. . IC50 values of RW-dried and sun-dried samples were evaluated by AAT bioquest Calculator using the following Eq.5. Where L0, a0, and b0 are values of fresh samples and L, a, and b are color values of dried samples in triplicates. A lab-scale batch RWD of a closed-loop control system was designed, fabricated and evaluated for drying rates, evaporation rate, the energy of evaporation, energy efficiency and throughput. Testing was done using mango and tomato pulps.

There was no significant difference in browning index between freeze-died and RW-died samples (A. Topuz, Dincer, Ozdemir, Feng, & Kushad, 2011; Ayhan Topuz, Feng, & Kushad, 2009). This study emphasised the relationship between drying temperature and aw, as increasing the drying temperature led to a reduction in the flakes’ aw; this could have been related to the fact that more water would have been evaporated at higher temperatures43. However, no mention was found in the pertinent literature of variation concerning drying temperature and its effect on aw, as most studies compare RW with other drying methods at a single temperature or vary drying times or sample thickness. The development of off-flavor is one of the major problems during storage which make food unacceptable.
Moisture content and temperature of storage greatly affects  the storage stability of RW dried powders. Pavan et al. found RW dried powder to be microbiologically safe, because of low water activity with good storage stability. Carotenes are colored pigments found many fruits and vegetables. Β-carotene is the most common form of carotene in plants. It can be used as a food coloring and it is a precursor to vitamin A. Carotenes are also susceptible to heat and oxidation (Pénicaud, Achir, Dhuique-Mayer, Dornier, & Bohuon, 2011) and their retention in dried products is imperative to achieve a high quality products.

Figure1 shows a laboratory-scale refractance window dryer that was used for this study. The main components of this refractance window dryer were a rectangular double wall water bath and a Mylar sheet 10 Mil (250  μm) thickness having properties such as high thermal resistance, water impermeability, and infrared waves permeability. Water bath temperatures were set from 50 to 90 °C and all samples were dried in triplicate at the above-mentioned temperatures. The temperature of the mylar sheet and walnut kernels was checked constantly.
InfraRWD offers lower drying cost comparing to other drying techniques. The results showed that mass transfer in salmon and beef was not improved by RW™. In contrast, in apple slices dehydrated using RW™, the Deff and processing times were significantly (paw of 0.6. Refractance Window drying is a safe way to dehydrate fresh whole foods.
Natural convection resulted in a higher average temperature at the different points of samples, while forced convection caused lower temperatures during the drying process. Drying curves also showed that the lowest moisture kinetics were obtained in samples dried with natural-convection, while the samples dried with forced-convection showed the highest moisture loss values. RW drying system uses circulating water at 90 to 95°C as a means to convey thermal energy to materials to be dehydrated . As the product does not have direct contact with the heat transfer medium during RW drying, no cross-contamination occurs (Moses, Norton, Alagusundaram, & Tiwari, 2014). Evaporation capacity up to 10 kg m−2 h−1 shows that RW is a very efficient drying process (Zotarelli, Carciofi, & Laurindo, 2015). Refractance Window is a new film drying method and it is characterized by maintaining a relatively low temperature inside the food and by requiring shorter process times (C. I. Nindo, Sun, Wang, Tang, & Powers, 2003).