Reverse Osmosis Membrane Technology for Concentrated Milk Production

Concentrated milk is manufactured by removing part of water from raw milk to increase the content of protein, fat and other solids. It can effectively reduce storage and transportation costs of milk raw materials and serve as a key intermediate raw material for various deep-processed dairy products. However, conventional vacuum evaporation concentration has inherent drawbacks. The material needs to be heated under reduced pressure for a long time, and the thermal environment is easy to trigger Maillard reaction, leading to browning of the product, weakening of fresh milk flavor and loss of natural active ingredients. Meanwhile, the evaporation system needs to consume a large amount of steam, resulting in high operating costs and large equipment footprint, which restricts the economic benefit of concentrated milk production.

Reverse osmosis is a pressure-driven membrane separation technology with extremely high interception precision. Driven by appropriate pressure, water molecules in milk can pass through the reverse osmosis membrane, while almost all dissolved solids such as milk protein, fat globules, lactose and mineral substances are trapped on the feed side, so as to realize continuous water removal and material concentration. Different from ultrafiltration and nanofiltration which have selective permeability to different solutes, reverse osmosis can intercept nearly all dairy components, and its core function is water separation and volume reduction.

In practical production, reverse osmosis concentration is generally used as a pre-concentration unit before vacuum evaporation. Raw milk first undergoes standard pre-treatment including clarification, degreasing and precision filtration to remove somatic cells, suspended particles and large impurities, preventing rapid membrane fouling caused by grease and protein deposits. The pre-treated milk enters the reverse osmosis skid for circulating concentration at room temperature or low temperature. After preliminary water reduction by the membrane system, the material liquid with elevated solid content enters the evaporator for final concentration. This combined mode greatly reduces the evaporation load and steam consumption of the subsequent thermal process.

The system adopts cross-flow circulation design. The milk flows rapidly parallel to the membrane surface, forming continuous scouring to reduce the adhesion of protein and fat on the membrane surface, slow down fouling rate and maintain stable water permeation flux. The whole concentration process does not require adding chemical additives. Supported by PLC automatic control, the system can adjust operating pressure and flow in real time according to the solid content of the feed liquid, realizing stable continuous production. The matched food-grade CIP cleaning system can effectively clean organic dirt after shutdown and restore the membrane performance for long-cycle operation.

Compared with single vacuum evaporation process, the composite process with reverse osmosis pre-concentration has outstanding economic and product advantages. It can save a large amount of steam energy, lower the overall production cost, and reduce the heating time of milk, so that the finished concentrated milk maintains fresher taste and better color. The modular skid-mounted reverse osmosis equipment is flexible to deploy, easy to be integrated into both new concentrated milk production lines and the renovation of old workshops.

Against the background of energy conservation and clean production in the food industry, reverse osmosis pre-concentration technology for milk has gained more and more recognition by dairy manufacturers. It balances production cost, product quality and energy saving requirements, and provides a reliable economical solution for the large-scale production of high-quality concentrated milk.