Researchers at Technische Universität München (TUM) are researching energy-efficient ways to process milk concentrates.
As a key ingredient in everything from infant formula to baked goods and confectionery products, powdered milk is something that is in constant demand in the food manufacturing sector, however the processes used to create it are highly energy intensive.
TUM researchers are currently combining different membrane separation processes which are resulting in a 20 percent reduction of the total amount of energy required to concentrate milk.
Professor Ulrich Kulozik from the TUM Chair of Food Process Engineering and Dairy Technology says that conventional methods of heating and evaporating the dairy products utilise membrane separation processes such as reverse osmosis and nanofiltration, followed by the drying of excess water. Although these methods are effective, drying can account for 50 percent of the entire energy consumption bill.
Kulozik explains that reverse osmosis and nanofiltration work with special membranes that allow water to pass through while retaining almost all constituents in milk and whey. One drawback being that the concentration of dissolved substances such as salt and lactose increases as more water is removed. Proteins also “block up” the membrane, reducing the amount of water being removed.
“As a result, we can only achieve a dry mass of up to 35 percent using reverse osmosis,” says Kulozik. “What we really want is a higher percentage of dry matter as this reduces the amount of water to be removed in subsequent evaporation and drying steps. This would further cut the energy consumed in the initial concentration stage.”
Prof. Kulozik and his team have been able to solve this problem by combining three different membrane separation processes: ultrafiltration, reverse osmosis and nanofiltration.
Ultrafiltration removes proteins from the liquid. The dissolved constituents can then be concentrated using reverse osmosis and nanofiltration. Removing the proteins in this way speeds up reverse osmosis and nanofiltration by a factor between two and five. This combination of reverse osmosis and ultrafiltration is 20-percent more energy efficient than reverse osmosis on its own. The proteins and dissolved constituents can be recombined at a later stage in the process chain.
“We were able to show that the right combination of membrane separation technologies can unlock significant efficiency gains in powdered milk and whey production,” adds Kulozik. “Our aim here is to obtain the highest possible concentrations of milk before evaporation and drying.”
Another project that the Tum team are working on includes extending the storage period of milk concentrates.
“We exploring various heating processes for concentrates with a view to extending the shelf-life for milk concentrate so that it becomes an attractive alternative to powder in the future,” says Kulozik.
“One of the main benefits of concentrates is that they are still liquid and so they do not need to be dissolved in water again,” says Prof. Kulozik. “And because there is no drying process involved, they also deliver significant energy and cost savings.”