Hereby, cold milk is first preheated and then further heated in a separate section for a few seconds up to 72°C. The major microorganisms present in the milk are destroyed during this process and as a result, the milk can be kept consumable for up to 10 days.
Analysis of pasteurized milk in the laboratory.
© Fraunhofer IGB
Currently, the milk is pasteurized by using plate heat exchangers in which preheated milk is passed in countercurrent to hot water or steam. The heat recovered from the subsequent cooling of the pasteurized milk is used to heat the incoming cold milk.
However, direct heating using plate heat exchangers has disadvantages: heat transfer is weakened by a process known as fouling, in which the heating time is extended by formation of an undesirable layer on the large surfaces of the heat exchanger.. They must therefore be cleaned regularly. Here, energy, water and detergents are required.
In the EU project MicroMilk, coordinated by the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB, different partners have developed a system that enables the preservation of milk and milk products with microwaves. A prototype for continuous microwave-pasteurization with a throughput of 400 liters of milk per hour has been integrated into an existing pasteurization process at a dairy station at the University of Hohenheim.
In experimental operation, great advantages have been shown. Reduction of fouling has enabled extended operating times between system cleansings, thus additionally saving water. Milk heating with a pasteurization step from 68°C to 72°C not only results in a more homogeneous temperature gradient, but is also three times faster than with a plate heat exchanger.
Due to this extremely rapid, almost sudden heating ("flash heating"), the milk is exposed to high temperatures only for very short time. "Much of the valuable and heat-sensitive substances, especially milk proteins and vitamin B remains undenaturated," explains Dr. Ana Lucia Vásquez, who coordinates the project at the IGB. “A very promising characteristic of microwave pasteurization is that we can also handle viscous products with a high content of solids, such as whey concentrates," Vásquez says. “Existing pasteurization plants are susceptible to fouling and have to be cleaned frequently.”
The core of the microwave method and a result of extensive simulation is a compact reactor, which is divided into different compartments. Each compartment is equipped with its own magnetron generating electromagnetic waves. The microwaves are coupled into a waveguide, which simultaneously acts as the heating chamber. Through this chamber, the milk flows in a special pipe. The pipe material does not absorb the microwaves, but is resistant against heat and pressure. Vásquez describes the principle:"During this passage, the milk is heated directly, and, unlike the plate heat exchanger, it is not heated from the outside to the inside, but volumetrically: when the electromagnetic waves are absorbed by the polar molecules of the milk, this makes the molecules oscillate over the entire volume and thus homogenously generating heat."
To provide the operational economics and to establish the system in the market, the process is now to be demonstrated with two industrial scale units within the follow-up project MicroMilk Demo. Dairies with a relatively small throughput can integrate the new microwave module into their existing plate heat exchanger system; the flexible microwave-pasteurization system enables discontinuous operation, allowing the processing of small throughputs to remain profitable. For this purpose, a microwave unit with a flow rate of 2,000 liters per hour is designed. The unit is specifically designed for the flash-heating of milk from ca. 67°C to 72°C, replacing the conventional heat exchanger and the associated heating circuit for pasteurization. However, the regeneration stage for heat recovery remains unaltered. "This makes the pasteurization system profitable for small dairies, since the system does not require a separate heating circuit or boiler for the start-up,” explains Vásquez.
The second microwave-pasteurization unit to be built has a flow rate of 1,000 liters per hour and will be tested to treat especially high viscous products such as condensed milk and whey concentrates, as well as products with a high content of solids such as fruit yogurt, fruit juice and fruit puree. This system is expected to operate without fouling formation and to heat dairy products to a wide temperature range of 60°C; fouling-prone plate heat exchangers will not be used.
Since September 2013, “MicroMilk-Demo – Demonstration of a novel microwave processing application for nutritional and shelf stable milk” is being funded within the scope of the 7th Framework Research Programme of the EU (Grant Agreement No. 606321). The project partners are the SMEs C. Van’t Riet Dairy Technology (Netherland), Dantech UK Ltd. (Great Britain), Malthe Winje Automasjon AS (Norway) and Schwarzwaldmilch GmbH Freiburg (Germany) with research partners the Fraunhofer IGB and University of Hohenheim.
Dr. Claudia Vorbeck | Fraunhofer-Institut
Harder 3D-printed tools – Researchers from Dresden introduce new process for hardmetal industry
11.10.2018 | Fraunhofer-Institut für Keramische Technologien und Systeme IKTS
Flying High with VCSEL Heating
04.10.2018 | Fraunhofer-Institut für Lasertechnik ILT
Innsbruck quantum physicists have constructed a diode for magnetic fields and then tested it in the laboratory. The device, developed by the research groups led by the theorist Oriol Romero-Isart and the experimental physicist Gerhard Kirchmair, could open up a number of new applications.
Electric diodes are essential electronic components that conduct electricity in one direction but prevent conduction in the opposite one. They are found at the...
Max Planck researchers revel the nano-structure of molecular trains and the reason for smooth transport in cellular antennas.
Moving around, sensing the extracellular environment, and signaling to other cells are important for a cell to function properly. Responsible for those tasks...
Researchers at the University of New Hampshire have captured a difficult-to-view singular event involving "magnetic reconnection"--the process by which sparse particles and energy around Earth collide producing a quick but mighty explosion--in the Earth's magnetotail, the magnetic environment that trails behind the planet.
Magnetic reconnection has remained a bit of a mystery to scientists. They know it exists and have documented the effects that the energy explosions can...
Biochips have been developed at TU Wien (Vienna), on which tissue can be produced and examined. This allows supplying the tissue with different substances in a very controlled way.
Cultivating human cells in the Petri dish is not a big challenge today. Producing artificial tissue, however, permeated by fine blood vessels, is a much more...
Faster and secure data communication: This is the goal of a new joint project involving physicists from the University of Würzburg. The German Federal Ministry of Education and Research funds the project with 14.8 million euro.
In our digital world data security and secure communication are becoming more and more important. Quantum communication is a promising approach to achieve...
19.11.2018 | Event News
09.11.2018 | Event News
06.11.2018 | Event News
21.11.2018 | Life Sciences
21.11.2018 | Power and Electrical Engineering
21.11.2018 | Life Sciences