Reconstituted Milk Processing

1. Reconstituted milk, also known as “recombined milk”, refers to concentrating and drying fresh milk into milk powder, and then using the milk powder as raw material, and adding an appropriate amount of water and other ingredients to make it into liquid milk with the same ratio of water and solids as in raw milk. Since reconstituted milk is produced with milk powder as raw material, compared with raw milk, the storage, transportation and shelf life of milk powder has a bigger advantage than fresh milk due to water being removed in milk powder.
2. The manufacturers are suitable for starting the reconstituted milk processing in their area in the following three situations: Some countries do not have enough fresh raw milk; In some areas, the fresh raw milk supply is not stable and regular; The raw milk transportation is in long distance and lack of the chilled conditions to store the fresh milk.
3. Although the reconstituted milk raw materials are in heat treatment through concentrating and spray drying processes, most of the nutrients are retained, especially the high-quality protein and calcium we want to obtain from milk. Heating these two components is almost not affected by high temperatures. Protein is mainly to provide amino acids to the human body, heat denaturation will not cause it to lose nutrients, but it will also help digestion and absorption. Calcium itself is an inorganic salt and will not change its structure when heated. At present, most reconstituted milk use UHT sterilization technology, which can kill harmful bacteria while retaining a large number of nutrients, and the safety of milk is effectively guaranteed.
4. The process for reconstituted milk includes milk powder dissolving, fats and flavors dissolving, liquid milk blending and formulation, milk homogenizing, degassing and UHT sterilizing, filling and packing into the containers. The whole production line involves a milk powder mixer, a high shear dissolving tank, blending tanks, UHT sterilizing system, a bottle/carton filling system, a packing system, RO pure water generating system, hot water generating system, a CIP system, pipelines, valves, and pumps. All the machines are made of SUS304/316L food-grade material.
5. The raw materials and ingredients for recombined milk production are skim milk powder or whole milk powder, pure water, stabilizers, emulsifiers, milk fat, flavors, etc.
6. The capacity of the reconstituted milk processing plant is from 500L/H to 10000L/H, and the end products can be filled into aseptic cartons, bottles or pouches, and the shelf life of the products can reach 6-12months.
7. The reconstituted milk processing line can be also used for producing recombined juice, yogurt and other recombined products.

Milk powder 

The quality of the milk power is very important for the final products. The particle size of the milk powder has a great relationship with the reconstitution, recovery and dispersion of the milk powder. When the particle size of the milk powder is 150μm, the reconstitution performance is the best, which can reach 99%. The milk powder used as reconstituted milk is preferably produced by centrifugal spray drying or pressure spray drying, and its particle size is between 30-200 μm. The whole milk powder or skim milk powder should be pale yellow. Not only the particle size and color of the milk powder, the water content(3%-5%), microorganism, fat globule (1-3μm) and protein should also be considered when choosing the raw materials.

RO pure water

Purified water is an indispensable and important raw material for the production of reconstituted milk. The water need to be pure drinking water, free from harmful microorganism and low hardness. The recommend pure water pH is 7-8, total solids less than 500mg/L, total hardness 5.5DH.

Milk fat

Anhydrous milk fat is used for producing the recombined milk. The fat content is ≥99.8, and the water content is ≤0.1%, it should be packed in oxygen-free containers.

Stabilizer and emulsifiers

Gelatin, Phosphates, Carrageenan, and Xanthan Gum can be added to the milk to stabilize the fats in milk and prevent sedimentation during storage. 0.2%-0.3% dosage can be added into the milk.

Here attached the reconstituted milk recipe for reference:

During the milk powder reconstitution process, milk powder is not directly added into the full amount of water. Instead, a high-concentration milk powder slurry is first prepared in a milk powder dissolving tank. Typically, milk powder is mixed with approximately 20–30% of the total required water at 55–60°C, forming a concentrated milk slurry with a solid concentration of around 35–45%.

After complete dispersion, the milk slurry is held for approximately 30–60 minutes to allow sufficient hydration of milk proteins, lactose, minerals, and other milk components. The fully hydrated milk emulsion is then transferred to blending tanks, where the remaining 70–80% of treated water is added according to the product formulation to achieve the required fat content, protein content, and total milk solids.

After blending and standardization, the reconstituted milk is processed through filtration, homogenization, and optional degassing. Homogenization reduces fat globule size and ensures uniform fat distribution, improving product stability and preventing cream separation. Degassing can be applied to remove dissolved air and reduce oxidation risks, improving the quality and shelf stability of the final product.

The standardized milk is then subjected to heat treatment. For UHT milk production, the product is typically sterilized at 135–150°C for approximately 2–10 seconds to eliminate microorganisms and achieve commercial sterility. In some production systems, pre-pasteurization (72–75°C for 15–20 seconds) may be applied before UHT treatment to reduce the initial microbial load and improve process stability.

After UHT sterilization and cooling under aseptic conditions, the reconstituted milk is transferred to an aseptic filling machine and packed into various containers, such as Tetra Pak cartons, PET bottles, or glass bottles, according to customer requirements and the selected packaging system. The final packaged UHT milk can then be safely stored and distributed at ambient temperature with an extended shelf life.

The milk powder reconstitution process is an important step in the production of reconstituted UHT milk. In this process, milk powder is mixed with water and fully hydrated to restore the composition and characteristics of fresh milk before further processing, including standardization, homogenization, UHT sterilization, and aseptic filling.

Milk powder and milk fat solids can be dissolved and emulsified in a milk powder dissolving tank equipped with a water powder mixer or high-shear mixer, depending on the required production capacity and dissolution efficiency.

The optimal dissolving temperature is typically 55–60°C. At this temperature range, milk powder can be rapidly hydrated and dissolved into a uniform liquid within approximately 30 minutes, while milk fat particles are effectively emulsified to improve product stability.

Milk powder can be added into the dissolving system either manually or automatically. For small-scale production, operators can manually feed milk powder into the water powder mixer. For large-scale industrial production, milk powder is usually transported and dosed automatically through a screw conveyor or screw elevator into the high-shear mixing system, ensuring continuous and controlled feeding.

In industrial milk processing plants, milk powder is generally not added directly into the full volume of water. Instead, a high-concentration milk powder slurry is prepared first to improve dissolution efficiency and reduce powder losses.

The typical process includes:

1. Water heating and preparation
   Treated water is heated to approximately 55–60°C to promote powder dissolution and protein hydration.
2. Powder feeding and high-shear mixing
   Milk powder is gradually introduced into the water under strong mixing conditions. The initial powder concentration is usually controlled at around 35–45%, which improves mixing performance and prevents powder agglomeration.
3. Hydration and holding
   After complete dispersion, the milk solution is held for approximately 30–60 minutes to allow milk proteins, lactose, minerals, and other components to fully hydrate.
4. Standardization and further processing
   After hydration, additional water, cream, or other dairy ingredients can be added to achieve the required composition before homogenization, UHT sterilization, and aseptic filling

Milk Powder and Water Ratio for Reconstitution

The ratio of milk powder to water depends on the type of milk powder and the required final milk composition. For commercial UHT milk production, the target is usually to achieve a composition similar to fresh cow milk, with approximately:

• Fat content: 3.0–3.8%
• Protein content: 3.0–3.5%
• Total milk solids: 12–13%

Whole Milk Powder Reconstitution

Whole milk powder typically contains:

• Fat: 26–28%
• Protein: 24–26%
• Total solids: approximately 96%

To produce standard whole milk, approximately:

1 kg of whole milk powder + 7–8 kg of water = 8–9 kg of reconstituted milk

For example, to produce 1,000 kg of reconstituted whole milk:

• Whole milk powder: approximately 120–130 kg
• Water: approximately 870–880 kg

The final product will have a composition close to fresh whole milk, with around 3.2–3.5% fat and 12–13% total solids.

After the milk powder and milk fat are fully dissolved and emulsified into a uniform milk emulsion, the mixture is transferred by a sanitary pump into the blending tanks. At the same time, the remaining amount of treated water is added into the blending tank according to the product formulation to achieve the required milk composition, including fat content, protein content, and total solids.

To prevent air incorporation during the mixing process, vacuum blending technology can be applied in the blending tanks. Vacuum mixing helps remove dissolved air and minimizes foam formation, improving product quality and ensuring better stability during subsequent homogenization and UHT sterilization.

For continuous industrial production, the blending system is usually equipped with two or three blending tanks operating alternately. While one tank is undergoing mixing or hydration, another tank can supply product to the downstream processing system, ensuring continuous operation of the UHT milk production line.

When the reconstituted milk is filled into the Tetra Pak package, before milk UHT treatment, it needs to be preheated to 60-70℃ for degassing and homogenization. After that, the milk will be heated to 137℃ and held for 3-5S for sterilizing by hot water indirect heating. and then the reconstituted milk will be cooled to 30℃ for aseptic filling.

When the milk is filled into the bottles, it will be heated to 60-70℃ for homogenizing and degassing, then the milk will be filled into the bottles directly, no need sterilization before filling, after filling into the containers, the reconstituted milk will be fed into the retort sterilizer for sterilization with 121℃ with 15-20minutes.

The reconstituted milk can be aseptically filled into Tetra Pak cartons, after filling, there is no need for secondary sterilizing.

The reconstituted milk can also be hot-filled or aseptically filled into the bottles. When hot filling, the milk in bottles will be sterilized again by the retort sterilizer, and then cooled to room temperature after labeling, date coding, and packing into the cartons or shrink packages.

A Reverse Osmosis (RO) water treatment system is essential for a reconstituted milk plant to ensure high-quality water free from impurities, bacteria, and dissolved solids, which is crucial for consistent milk reconstitution. The RO water treatment system includes the water storage tanks, pre-filtration system(sand filter, carbon filter, and ion exchanger), RO equipment, and Ozone/UV water sterilizer. The tap water or ground water after RO treatment can be used for process water in reconstituted milk plant for milk powder dissolving and final milk volume fixing.

A Cleaning-in-Place (CIP) system is essential for maintaining hygiene and ensuring product quality in a reconstituted milk plant. It allows the automatic cleaning and sanitization of tanks, pipelines, pasteurizers, UHT systems, and filling machines without dismantling the equipment. The main function of CIP system in reconstituted milk processing plants is as follows:

• Removes milk residues, fats, proteins, and microbial contaminants
• Prevents bacterial growth and cross-contamination
• Ensures compliance with food safety standards (e.g., HACCP, FDA, EU regulations)
• Reduces downtime and labor costs compared to manual cleaning