Powdered milk, also known as dried milk, is a dairy product made by evaporating milk to dryness, significantly extending its shelf life and reducing its volume and weight for easier storage and transport. The process involves several key steps that transform liquid milk into its dry, powdered form.
The Journey from Liquid to Powder
The manufacturing of powdered milk primarily focuses on removing the vast majority of water content from fresh milk while preserving its nutritional value.
1. Raw Milk Reception and Pre-treatment
The process begins with fresh, high-quality raw milk. Upon arrival at the factory, the milk undergoes rigorous quality checks.
- Standardization: The fat content of the milk is adjusted to a desired level, depending on whether the final product will be full-fat, skimmed, or semi-skimmed milk powder.
- Filtration: Impurities are removed from the milk through filters.
- Pasteurization: The milk is heated to a specific temperature for a set period (e.g., 72°C for 15 seconds) and then rapidly cooled. This step eliminates harmful bacteria while retaining the milk's nutritional qualities, ensuring food safety.
2. Evaporation/Concentration: Making the Milk Thicker
After pre-treatment, the milk is transferred to large evaporators. This is a crucial step where a significant amount of water is removed from the milk.
- Process: The milk is heated under a vacuum, which allows water to boil off at lower temperatures, preventing damage to heat-sensitive nutrients.
- Purpose: As stated in the provided reference, "milk is mostly water. And by removing. Some we make the milk thicker. And ready for the next step." This pre-concentration step reduces the water content by about 85-90%, turning liquid milk into a thick, concentrated liquid known as condensed milk. This also makes the subsequent drying process more energy-efficient.
3. Spray Drying: The Real Magic
Once the milk has been concentrated, it's ready for the final drying stage, which the reference describes as "where the real magic. Happens. It's called Spray drying."
- Mechanism: The concentrated milk is atomized into a fine mist of droplets within a large drying chamber. These droplets are then introduced into a stream of hot air (typically between 180-250°C).
- Instant Drying: The hot air rapidly evaporates the remaining water from the tiny droplets, leaving behind solid milk particles. The particles are then separated from the air, often using cyclones. This rapid drying process prevents the milk from being exposed to high temperatures for too long, preserving its quality.
4. Cooling and Packaging
The fine milk powder produced from spray drying is still warm.
- Cooling: The powder is cooled to ambient temperature to prevent caking and ensure stability during storage.
- Sifting: It may be sieved to ensure uniform particle size and remove any clumps.
- Packaging: The cooled milk powder is then packaged into airtight containers, bags, or pouches. Proper packaging is essential to protect the powder from moisture and oxygen, which can degrade its quality and shorten its shelf life. Packaging materials often include multi-layered bags with an inner aluminum foil layer.
By following these precise steps, fresh liquid milk is transformed into a stable, long-lasting powdered form, ready for various uses, from baking and cooking to rehydrating for consumption as liquid milk.