RWD vs Spray Dryer for Spirulina Production: Why Koppex Spirulina Uses Refractance Window Drying
- karthik rajoor
- 1 day ago
- 4 min read
Why drying method matters more than you think?
Spirulina (Arthrospira/Spirulina) is valued for its naturally occurring pigments especially phycocyanin and other bioactive compounds. But those same compounds are sensitive to processing. Fresh spirulina biomass is also highly perishable due to its high moisture, making drying essential for safe storage and consistent industrial use.
That’s where the choice of dryer becomes strategic. Two common industrial approaches: Spray Drying and Refractance Window Drying (RWD).
What is Refractance Window Drying (RWD)?
In RWD, spirulina biomass (typically a slurry/paste) is spread as a thin layer on a flexible film (often referenced as Mylar®) that sits over hot water. Heat reaches the product through a combination of conduction, convection, and radiation. A key practical advantage: during early and mid drying, the product temperature is commonly ~20–25°C lower than the hot water due to evaporative cooling—helping reduce thermal stress on sensitive compounds.
Research on spirulina specifically found RW drying can produce a dehydrated product with <10% moisture, minimal visual change.
What is spray drying?
Spray drying atomizes a liquid feed into fine droplets and exposes them to a hot air stream, rapidly removing moisture and forming powder particles. It is widely used because it produces a fine, consistent powder and is considered highly scalable for large volumes but it is often described as energy- and cost-intensive at scale.
A common temperature window reported for conventional spray drying is ~140–200°C inlet air temperature (with outlet temperature being a consequence of the operating balance). For microalgae specifically, a review summarizes “optimal” ranges (depending on goals) around 150–170°C inlet and 40–80°C outlet to help retain bioactives while maintaining efficiency.
RWD vs Spray Drying for spirulina: side-by-side comparison
Factor | RWD (Refractance Window Drying) | Spray Drying |
Thermal stress on pigments | RWD exposes spirulina to a gentler temperature profile, resulting in reduced thermal load. | Spray drying exposes spirulina to elevated inlet temperatures and rapid heat transfer, which can increase thermal load. |
Phycocyanin retention strategy | Supports higher phycocyanin preservation. | High thermal exposure requires careful parameter control to reduce phycocyanin loss. |
Need for carriers (e.g., maltodextrin) | Not required for whole-biomass drying. | Frequently used in spray drying to reduce stickiness, improve yield. |
Output form | Often flakes/sheets that can be milled into powder. | Fine, free-flowing powder directly. |
Powder behavior | Milling step can tune particle size; good for tablets/functional powder blends | Good for instantized/fine powder applications. |
Scalability maturity | Commercially used, but less universal than spray drying. | Very mature industrially; highly scalable for continuous production. |
Energy profile (general) | Reviews often highlight efficiency and quality retention for heat-sensitive materials . | Conventional spray dryers commonly reported around 1.6–2 kWh/kg evaporated water (varies widely by system) |
The “quality” question: color, pigments, and bioactives
What this means in practice:
If your buyers care about vibrant color and pigment-linked specs, the method that better controls thermal stress is often preferred especially when the product is meant for clean-label food and beverage or as a functional ingredient where appearance signals quality.
Visual quality and browning risk:
In RWD drying of spirulina biomass, researchers noted minimal visual changes and absence of common browning/carbonization regions under their test conditions an important note for ingredient buyers who judge spirulina quickly by color.
The “formulation” question: do you want 100% spirulina or an engineered powder?
Carriers and encapsulation in spray drying:
In many spray drying applications especially for sensitive bioactives or sticky feeds carrier agents (maltodextrin, gums, proteins) are used to improve powder recovery, reduce stickiness, and protect actives.
That can be a benefit if you want:
microencapsulation for stability or taste masking.
easier handling and flow properties.
improved dispersibility for specific beverage systems.
But it may be a drawback if your market expects:
Clean-label “100% spirulina”
No added carriers or diluents.
a straightforward ingredient declaration.
Why Koppex Spirulina is produced using RWD
Koppex focuses on producing spirulina as a natural functional ingredient. For that category, the most consistent purchasing drivers are:
Color fidelity (a quick quality signal for buyers).
Bioactive integrity (especially pigment-linked specifications).
Clean-label simplicity (no carriers used).
Given published evidence that RWD drying can deliver dried spirulina with low moisture, minimal visual change, and that phycocyanin is sensitive to higher temperatures and long exposure, the RWD approach is a strong technical fit for premium, functionality-led spirulina positioning.
If you’re formulating for food, nutraceuticals, or natural color systems, RWD is often the drying method that supports the story buyers want: gentle processing to protect what matters.
Applications: where RWD-dried spirulina can shine:
Tablets & capsules
Functional foods: nutrition bars, premixes, savory nutrition blends.
Beverages & smoothie bases
Natural color development: as a base ingredient for pigment-focused innovation.
Buyer checklist: what to ask your spirulina supplier (practical & spec-driven)
Drying method used (RWD vs spray vs others) and why
Moisture (%) and water activity (aw)
Particle size distribution (as-is or post-milling)
Color metrics
Microbial specifications and batch COA
Carrier agents or additives
Application guidance (dosage, dispersion, taste masking options)
Regulatory documentation relevant to your market
Conclusion
Spray drying is a industrial workhorse, fast and good for fine powders and engineered encapsulates. But for whole spirulina biomass where customers care deeply about natural color, pigment integrity, and clean-label positioning, Refractance Window Drying (RWD) offers a compelling quality pathway supported by spirulina-specific research and broader RWD reviews.
That’s why Koppex Spirulina is produced using RWD to align the drying technology with what functional ingredient buyers value most.
Interested in a technical data sheet, or application guidance? Reach out to info@koppexls.com for product specifications, formulation support and samples.
Source links:
1) Spirulina + Refractance Window Drying study (MDPI Molecules, 2023):
2) RWD review: trends, quality retention, process comparisons (Food and Function, 2021; ScienceDirect page):
3) Spray drying overview + variables + typical inlet temperature range (MDPI Processes, 2020):
4) Microalgae spray drying conditions summary (ScienceDirect, 2025):
5) Spirulina drying methods overview including spray drying scalability and cost notes (MDPI Separations, 2024):
6) Carrier agent role in spray drying (AIP Conference Proceedings PDF, 2023):
7) Industrial drying energy reference including conventional spray dryer ranges (SINTEF HighEFF PDF, 2017):
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