new food product development
                     
REFRACTANCE WINDOW 
DRYING
NEW TECHNOLOGY
Date: 16th November 2022
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INTRODUCTION
• A novel drying method for producing high-quality powders, flakes or sheets from fruits, vegetables 
or herbs concentrate in an efficient time and energy.
• MCD technologies ( Tacoma, Washington) designed the Refractance window dryer, patented by 
Richard Magoon in 1989.
• Sun drying and hot air drying cause significant loss of colour, making the product less appealing to 
consumers and resulting in loss of nutrient content and rehydration ability.
• Drum drying, developed for liquid products, causes severe quality loss in the product due to 
exposure to high temperatures (120-170°C) [1]. 
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• Spray-dried products often suffer from high volatile losses due to atomization and high air 
temperature of 150-300°C (although the temperature of most particles may remain at the wet 
bulb temperature of the air), as well as significant nutrient losses [2].
• Freeze drying is a commercial process that can produce high-quality dehydrated products with 
good retention of shape, flavour, colour, nutrient content, and rehydration ability. However, the 
cost of producing freeze-dried products is very high, up to ten times the cost of using forced hot 
air drying.
• Refractance window drying helps address the problems that occur with other drying methods.
• The process uses 50 – 70% less cost and more than 50% less energy than freeze-drying [3].
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WORKING PRINCIPLE
• Refractance Window (RW) 
drying technique uses hot 
water as the source of heat.
• Mylar sheet acts as a 
medium which transmits IR 
radiation and conducts heat 
to the product to be dried [
4].
Figure 1: Schematic view design of  RW [2]
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COMPARISON WITH OTHER TECHNIQUES:
Figure 2: Mango powder at different particle slices obtained from 
different drying methods[5]
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ADVANTAGES
• Lower installation and operation costs
• Shorter drying times
• Reduced Nutrient loss(Vitamins, Carotenoids, Antioxidants, Ascorbic acid)
• Reduced Microbial activity (E.coli, Innocula microbial activities)
• Increased shelf life 
• No cross-contamination occurs.
• Refractance window drying requires less capital and 50% less energy than the 
freeze drier.
• A significant reduction of microbial load can be observed with refractance 
window heating.
• The dried food products had better quality with RW drying than other 
methods. [2].
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CONCLUSION
 The refractance window drying method uses low temperatures, at less time and provides better 
colour, flavour, nutritional and textural properties in fruit leather production [4].
 Concerning microbial reduction ability, Refractance Window achieved at least reductions for 
total aerobic counts, coliforms, E. coli, and L. innocua microbial activities [2]. 
 The studies conducted on the Refractance Window drying technology show that the system 
demonstrates high retention of product quality (colour, vitamins, and antioxidants) when 
compared with other conventional drying methods.
 These attributes of RW drying make it suitable for processing of high-value foods, 
nutraceuticals, and food supplements where high standards of quality and safety are required. 
Additionally, RW drying technology can be used in parts of the world where effective drying 
methods such as freeze drying have been challenging to implement due to their high cost [1].
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References 
1) https://www.foodonline.com/doc/refractance-window-food-drying-system-deliver-0001
2) https://www.tandfonline.com/doi/abs/10.1080/07373930601152673
3) https://www.sciencedirect.com/science/article/abs/pii/S0924224421001370
4) https://onlinelibrary.wiley.com/doi/abs/10.1002/jsfa.9356
5) https://www.sciencedirect.com/science/article/abs/pii/S0260877412000301
 
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THANK YOU 
M1.  
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