Spray drying is the primary method used to convert liquid milk into milk powder, a product prized for its long shelf life, convenience, and versatility. The process is widely used in the dairy industry to produce whole milk powder, skim milk powder, and instant milk powder. Understanding the milk spray drying process is essential for dairy manufacturers, food technologists, and process engineers to ensure high-quality, nutrient-rich, and stable powder.

What is Spray Drying?

Spray drying is a thermal dehydration process in which liquid milk is atomized into fine droplets and exposed to hot air. The water evaporates almost immediately, leaving behind dry milk particles. This method is preferred because it:

• Preserves nutritional value

• Produces fine, uniform powder

• Ensures solubility

• Extends shelf life

Spray drying is suitable for both industrial-scale production and specialized applications like infant formula and instant beverages.

Step 1: Milk Collection and Quality Testing

The process begins with fresh raw milk collected from dairy farms. Before processing, milk undergoes testing for:

• Fat and protein content

• Total solids

• Microbial load

• Temperature and acidity

High-quality milk is critical because variations can affect the texture, solubility, and nutritional value of the final powder.

Step 2: Standardization

Milk is standardized to achieve the desired fat and solids content.

• Whole milk powder retains higher fat content.

• Skim milk powder has almost all fat removed.

Standardization ensures consistent viscosity, flow, and powder quality during spray drying.

Step 3: Pasteurization

Pasteurization eliminates harmful microorganisms. Common methods include:

• High-Temperature Short-Time (HTST): 72°C for 15 seconds

• Ultra-High Temperature (UHT): 135°C for a few seconds

Accurate temperature control is essential. Overheating can damage proteins, while underheating may compromise food safety.

Step 4: Evaporation and Concentration

Before drying, milk is concentrated using vacuum evaporators to remove water. This step increases total solids from about 12% to nearly 50%.

Viscosity and flow must be monitored carefully to prevent equipment blockages and ensure uniform drying. Industrial solutions from companies like Lonnmeter help maintain optimal conditions.

Step 5: Homogenization

Homogenization reduces the size of fat globules and distributes them evenly throughout the milk. Benefits include:

• Improved stability

• Reduced fat separation

• Enhanced solubility

This step ensures a high-quality, uniform powder.

Step 6: Atomization

The concentrated milk is then atomized into fine droplets. Atomization methods include:

• Pressure nozzles: High-pressure milk is forced through a nozzle to form droplets

• Rotary atomizers: Milk is spun from a rotating disc to create fine droplets

Droplet size affects solubility, bulk density, and particle uniformity.

Step 7: Spray Drying

The atomized droplets are exposed to hot air (inlet temperature 160–200°C, outlet 80–90°C) inside a spray drying chamber. Water evaporates instantly, forming dry milk particles.

Key factors in spray drying:

• Air temperature: Must remove moisture efficiently without scorching

• Residence time: Ensures complete drying while preserving nutrients

• Droplet size: Determines particle characteristics and solubility

Spray drying produces fine, uniform, free-flowing milk powder suitable for storage and industrial applications.

Step 8: Fluid Bed Drying and Cooling

After spray drying, the powder may pass through a fluid bed dryer to:

• Remove residual moisture

• Cool the powder

• Prevent caking

This step ensures shelf stability and solubility.

Step 9: Agglomeration (Optional for Instant Milk Powder)

For instant milk powder, agglomeration is performed. Fine particles are lightly moistened and dried to form larger, porous granules, which:

• Dissolve quickly in water

• Improve mixing properties

• Reduce clumping

Step 10: Sieving and Quality Control

The milk powder spray drying process is sieved for uniform particle size and tested for:

• Moisture content

• Bulk density

• Solubility

• Microbial safety

These checks ensure the product meets industry and regulatory standards.

Step 11: Packaging

Finally, milk powder is packaged in moisture-proof containers, such as:

• Bags

• Cans

• Bulk silos

Proper packaging protects against humidity, oxidation, and contamination, ensuring long shelf life.

Advantages of Spray Drying

Spray drying provides several benefits:

• High nutrient retention

• Uniform particle size and solubility

• Extended shelf life

• Suitable for instant reconstitution

• Scalable for industrial production

Applications

Spray-dried milk powder is used in:

• Infant formula

• Beverages: Milkshakes, coffee mixes, and nutritional drinks

• Bakery and confectionery: Cakes, chocolates, and desserts

• Food ingredients: Yogurts, sauces, and cheese

Importance of Process Monitoring

Monitoring is crucial to ensure consistent quality. Parameters such as viscosity, moisture content, flow rate, and temperature must be controlled. Lonnmeter provides industrial measurement solutions for real-time monitoring, improving efficiency and product consistency.

Conclusion

The milk spray drying process efficiently converts liquid milk into stable, nutrient-rich powder through a series of controlled steps:

1. Milk collection and testing

2. Standardization

3. Pasteurization

4. Evaporation and concentration

5. Homogenization

6. Atomization

7. Spray drying

8. Fluid bed drying and cooling

9. Optional agglomeration

10. Sieving and quality control

11. Packaging

Each stage requires precision and control to ensure the final milk powder is soluble, safe, and high-quality. Industrial monitoring solutions like those from Lonnmeter help manufacturers achieve optimal production efficiency, consistency, and safety.