REFRACTANCE WINDOW DRYING

KITTUR RANI CHANNAMMA COLLEGE OF HORTICULTURE, ARABHAVI
Seminar-II
Archana S. Pattar
Ph.D(IInd year)
UHS17PGD197
Postharvest Technology
University of Horticultural Sciences, Bagalkot
29/3/2019 1Dept.Postharvest technlogy

Refractance window drying??
Working Principle
Parts and specifications
Evaluation of refractance
window drying
Case study
Conclusion29/3/2019 2Dept.Postharvest technlogy

A novel drying method for production of high quality powders,
flakes or sheets from fruits, vegetables or herbs concentrate in an
efficient time and energy.
REFRACTANCE WINDOW DRYING??
Vahid et al.,2010

MCD technologies,(Tacoma,Washington) designed the Refractive
Window dryer which was patented by Richard Magoon in 1989
RW drying process uses 50–70 % less cost and more than 50 %
less energy than the freeze-drying
Short drying time (2-6 minutes)
ORIGIN OF RW DRYING METHOD
Deepika and Ashis, 2018

Pureed fruit and vegetable
Herbal formulations
Egg mixtures
Meat powder
Pharmaceutical
Nutraceutical
Cosmetics
Applications of RW

Working of RW dryer
RW drying technique uses hot water as the source of heat
Mylar sheet as a medium which transmit IR radiation as well as
conduct heat to the product to be dried

When water is heated
Fig 1: THE REFRACTANCE WINDOW PRINCIPLE
Maharshi et al.,201729/3/2019 7Dept.Postharvest technlogy

When hot water is covered by IR
Maharshi et al., 201729/3/2019 8Dept.Postharvest technlogy

When wet product is applied on IR membrane

When the dried product is obtained

Fig 2: Schematic diagram of the Refractance window drying unit
Moses et al., 2014

Evaluation
of RW
drying
Heat
transfer
and drying
kinetics
Product
quality
Thermal
efficiency
Energy
consumptio
n
Drying
efficiency
and cost
Drying kinetics
It takes 6 minutes to remove 1kg of water from carrot puree with the Refractance
Window™ system, whereas it takes 120 minutes to remove 1 kg of water in the tray
drier

Table 1: Comparison of carotene losses in carrot due to RW drying with
other methods
Treatment Alpha-Carotene
loss %
Beta-Carotene
loss %
Total carotene
loss %
RW dried 7 10 9
Freeze dried 2 5 4
Drum dried 55 57 56
Convection oven 24
Food dehydrator 18
Microwave oven 28.63
Air dried 82 72
Explosive puff
dried
36
Maharshi et al., 2017

Fig 3: photographs of mango flakes or powder at different particle slices
obtained from different drying methods
Caparino et al.,2012

29/3/2019 Dept.Postharvest technlogy 15
Table 2: Microbial count in log cfu/ml as affected by RW drying of of
inoculated pumpkin purees

Thermal Efficiency
• RW having 28-48% for pilot scale and 52 to 70% for commercial
scale when compared with other dryers.
CI Nindo, 2003
Energy Consumption
•Total energy consumption for dehydrating a 150g batch was only 375-
525 W for RW system which was considerably lower than 70-84kW for
freeze drying

Table 3: Comparison of evaporative capacity and thermal efficiency of
Refractance Window drying system with selected dryers
Deepika Shende and Ashis Kumar, 2018
Dryer Energy
requirement
kW
Evaporative Capacity
kg H2O hr-1m-2
Thermal
Efficiency
%
Convection 20-35 0.3-1.8 35-40
Spray 11-13 1-30 20-51
Drum 2.11-4.41 6-20 35-78
Freeze 130.65 0.0027-0.0037 30-32
RW-pilot 11.5-13.8 4-8 52-72
RW-Full
scale
15.81-17.54 3.1-4.6 33.3-53.2

Table 4: Comparison of average drying efficiency and cost for producing 1kg of
tomato powder by RW dryer and convection dryer
Item
Tomato dried by
Convection
drying
Refractance window drying
60⁰C/16hr 90⁰C/40 min 75⁰C/60
min
60⁰C/75
min
Average drying
efficiency
7.9 51 35.6 29.8
Yearly cost 4656.01 5389.23 - -
Cost(/kg
powder)
60 14.31 17.02 21.34

Lower installation and operation costs
Shorter drying times
No cross-contamination occurs
Requires 50–70% less capital and 50% less energy than the
freeze drier
Reduction from 4 to 6 decades of microbial load
Better quality of dried products
Advantages
Nindo and Tang ,2007

Objective: To compare the RW and tray drying
techniques with regard to the kinetics of drying, and
water activity of mango slices
Drying characteristics of mango slices using
the Refractance Window technique
Journal of Food Engineering 109 (2012) 69–75
C.I. Ochoa-Martínez , P.T. Quintero, A.A. Ayala, M.J. Ortiz
School of Food Engineering, Colombia

Treat
ment
Drying Thickness Time
T1 RW
drying
1 and 2 mm 10, 20, 30 and
60 min
T2 Tray
drying
1 and 2 mm 20, 40, 60, 120,
180 and 240
min
Drying
(Different methods)
Slicing
(1&2mm)
Washing
Selection
Ochoa et al.,2012
Treatment Details
Weight :500 g
TSS : 13.9°Brix
Moisture content: 83 to 86%
29/3/2019
22Dept.Postharvest technlogy

Fig 1: Kinetics of moisture content for RW and tray drying for 1 mm and
2 mm samples
Ochoa et al.,2012

Fig 2: Kinetics of moisture content for RW and tray drying at 90° C for
1mm and 2mm
Ochoa et al.,2012

Fig 3: Water activity behaviour for RW and tray drying for 1mm and
2mm samples
Ochoa et al.,2012

Objective: To produce Pomegranate
juice powder using RW dryer, a
freeze dryer and a spray dryer
Refractance Window drying of pomegranate juice:
Quality retention and energy efficiency
LWT - Food Science and Technology- 2015
Vahid Baeghbalia, Mehrdad Niakousaria, Asgar Farahnakya
Department of Food Science and Technology, Shiraz University, Iran
Email: niakosar@shirazu.ac.ir

T1 - Freeze dryer
T2- RW dryer
T3- Spray dryer
Vacuum packed in
polyethylene bags
Drying
(Different methods)
PJ concentrate( 64°brix)
Treatment Details
Vahid et al., 2015

Sample Moisture content
(% Wet basis)
Yield
(%)
Bulk density
(kg/m3)
Solubility
(%)
Freeze dried 8.55±0.57a* 96.7±0.3a 430.1±8.9a 89.1±0.5b
RW dried 5.38±0.57b 95.2±0.3b 343.1±8.9b 92.9±0.5a
Spray dried 2.92±0.57c 78.1±0.3b 322.1±8.9b 93.5±0.5a
Table 1. Moisture content, yield, bulk density and solubility of pomegranate
juice powder produced by spray, freeze and Refractance Window drying
methods.
* Different letters in each column indicate a significant difference (p ≤0.05)
Vahid et al., 2015

Sample AC TAC AA TPC
Freeze dried 0.247±0.018 b 9.017±0.447 c 12.656±2.113 b 571.0±5.044 a
RW dried 0.232±0.018 b,c 10.771±0.447 b 12.947±2.113 b 534.2±5.044 b
Spray dried 0.183±0.018 c 7.723±0.447 c 9.979±2.113 c 511.9±5.044 c
Table 2. Anthocyanin color, total anthocyanins content, antioxidant activity and total
phenolic compounds of samples dried by spray, freeze and Refractance Window
drying methods
AC: Anthocyanin color, TAC: Total anthocyanins content (mg cyanidin-3-glucoside/100 ml of
PJ), AA: Antioxidant activity (%), TPC: Total phenolic compounds (mg equivalent gallic acid)
Vahid et al., 2015

Sample Calculated
energy
needed for
drying
1kg sample
(kWh)
Energy
consumption
for drying
1kg sample
(kWh)
Overall
energy
efficiency (%)
CO2 Emission
for drying
1kg
sample (kg)
Freeze
dried
1.46 130.65±0.82 a* 1.12 104.52
RW dried 1.36 4.31±0.82 c 31.56 3.45
Spray
dried
1.42 11.01±0.82 b 12.92 8.81
Table 3: Overall energy efficiency of spray, freeze and Refractance
Window dryers.
Vahid et al., 2015

Objective: To compare the
RW output to the output
of hot-air drying.
The advantages of the Refractance Window
method of dehydrating fresh tomato slices
J. Appl. Environ. Biol. Sci., 4(11S)6-13, 2015 ISSN: 2090-4274
Azar Abbasid, Mehrdad Niakousari, Seyed Ali Yasini Ardekani
Department of Food Science and Technology, Shiraz University, Iran

Treatment Details
Packed in polyethylene bags
Drying (Different methods)
Slicing (2mm)
Washing
Selection
T1 Hot air dried
T2 RW dried
Azar et al., 201529/3/2019 32Dept.Postharvest technlogy

Figure 1. The curve pertaining to moisture change when drying at 75 ºC
and 90 ºC (a: the hot-air drier; b: the RW)
(a) (b)
Azar et al., 2015

0
10
20
30
40
50
60
Fresh Hot air
75
Hot air
90
RW 75 RW 90
0
10
20
30
40
50
60
70
Fresh Hot air
75
Hot air
90
RW 75 RW 90
0
10
20
30
40
50
60
Fresh Hot
air 75
Hot
air 90
RW
75
RW90
Fig 2: Parameters of colour analysis
for the fresh and dried slices of tomato,
dried at 75 ºC and 90 ºC via the hot-air
drier and the RW.
L*
a*
b*
(A) L*: Brightness.
(B) a*: Redness
(C) b*: Yellowness
(A)
(B)
(C)
Azar et al., 2015

0 5 10 15 20 25
Hot air 75
Hot air 90
RW 75
RW 90
Fig 3: The total changes in colour (∆E) of the dried samples treated with 75 ºC
and 90 ºC via the hot-air drier and the RW
Azar et al., 2015

Fig 4: The total phenol content of fresh samples and the dried are depicted with
differences being noticeable between the two temperatures and the two methods,
expressed in milligrams of gallic acid equivalent.
280
285
290
295
300
305
310
Fresh Hot air 75 Hot air 90 RW 75 RW 90
TotalPhenolcontent(mg/gdrymatter)
29/3/2019 36Dept.Postharvest technlogy Azar et al., 2015

Objective: Evaluation of the
major capsaicinoid contents of
the fresh and rehydrated red
Jalapeno pepper slices after
different drying methods
Effect of Different Drying Methods and Storage on Physico-chemical
Properties, Capsaicinoid Content, Rehydration Ability, Color
Parameters and Bioactive Compounds of Dried Red Jalapeno Pepper
(Capsicum annuum) Slices
Middle East J. Appl. Sci., 6(4): 1012-1037, 2016
Enssaf M. A. El-Hamzy and Mohsen M. S. Ashour
Food Science & Technology Department, National Research
Centre, Dokki, Cairo, Egypt
E- mail: mohsen_ashour @yahoo.com
ISSN 2077-4613

Treatment Details
Drying(Different
methods)
*Pretreatment
Blanching (85 °C for
4min )
Slicing (6±1mm)
Washing
Selection
Enssaf et al., 2016
*Pretreatment :15% NaCl, 1.0% CaCl2 and 0.3%
Na2S2O5 for 10min
T1 RWD1 unblanched
T2 RWD2 blanched
T3 OD1 unblanched
T4 OD2 blanched
T5 SD1 unblanched
T6 SD2 blanched
RWD-Refractance window drying
OD-Oven drying
SD-Sundrying

Table 1: Relative capsaicinoid contents of the fresh and dried red Jalapeno slices
obtained by different drying methods.
Enssaf et al., 2016
RWD1 unblanched OD1 unblanched SD1 unblanched
RWD2 blanched OD2 blanched SD2 blanched

Fig 1: Effect of different drying methods of the red Jalapeno slices on
the capsaicinoids during storage at room temperature
Enssaf et al., 2016RWD1 unblanched OD1 unblanched SD1 unblanched

Fig 2:Interaction between rehydration ratio (RR) and water holding capacity
(WHC) of the rehydrated red Jalapeno slice dried by different drying methods
Enssaf et al., 2016

Fig 3: Effect of different drying methods of the red Jalapeno slices on
the non –enzymatic browning and ASTA coloue value
Enssaf et al., 2016

Objective: To evaluate the main changes
in physico-chemical properties of
dehydrated Aloe vera gel obtained by
different drying procedures
Effect of different drying procedures on
physicochemical properties and flow behavior of
Aloe vera (Aloe Barbadensis Miller) gel
LWT - Food Science and Technology-2016
R. Minjares-Fuentes, A. Femenia, F. Comas-Serra, C. Rossello, V.M.
Rodríguez-Gonzalez, R.F. Gonzalez-Laredo, J.A. Gallegos-Infante, L.
Medina-Torres
Department of Chemistry, University of the Balearic Islands, Spain
Email:antoni.femenia@uib.es

T1- Reference
T2- Spray-drying
T3- Freeze-drying
T4-Refractance window dryer
T5-Radiant zone-drying Packed in polyethylene
bag
Drying
(Different methods)
Extaction of alovera gel
Washing
Alovera leaves
(40-50cm lenth)
Treatment Details
Minjares et al.,201629/3/2019 44Dept.Postharvest technlogy

Fig. 1. Flow chart of the dehydrated Aloe vera gel using different drying
procedures

Table 1: Water activity of Aloe vera samples
Sample aw
Reference 0.365a±0.001
Spray-drying 0.347b± 0.002
Freeze-drying 0.297c± 0.003
Refractance window dryer 0.345d±0.000
Radiant zone-drying 0.336e±0.003
Minjares et al.,2016

Fig 2: Morphology of Aloe vera samples: (a) Aloe vera reference, and Aloe
vera dehydrated by (b) spray drying (c) freeze drying (d) refractance
window and (e) radiant zone-drying
(a) (b) (c)
(d) (e)

Fig. 3. Solubility of the different Aloe vera samples: (●) Aloe vera reference, (○)
Aloe vera SD, (▼) Aloe vera FD, (∆) Aloe vera RWD, and (■) Aloe vera RZD
All solubility determinations were carried out in triplicate. (n = 3)

Fig. 4. Hygroscopy of Aloe vera dehydrated by the different drying
procedures

COMPANIES WHICH USE REFRACTANCE
WINDOW
Company Name Manufacture
Mega Food
New Hampshire
Whole food supplements from fruits and
vegetables
NutraDry
Australia
Whole food powders” from fruits, vegetables
and meats
Cerule
Oregon
algae

Low capacity of system
Inconvenient handle powders with high sugar contents
Limits

CONCLUSION

REFRACTANCE WINDOW DRYING

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