Filtration systems

How can you improve the result of pasteurization, preserving the taste and all the useful properties of milk? It’s easy! Back in 2007, scientists at Cornell University found that microfiltration could extend the shelf life of pasteurized milk up to 14 weeks. And “microfiltered” cheeses can retain the taste of “unpasteurized” cheeses, and it will be really safe.

What is membrane filtration

Membrane filtration is a modern method of cleaning milk from bacteria and/or separating it into its components. The following membrane filtration methods are used in commercial milk and dairy products production: microfiltration, ultrafiltration, nanofiltration, reverse osmosis, and there is also a process that is inseparable from the membrane filtration process; it is microparticulation. Each of these types of units has a different membrane pore diameter, so their areas of use

What types of membrane filtration exist?

1. Microfiltration

Microfiltration is a process carried out at low pressure. The filtration of the product is done by a membrane which retains insoluble components.

Pore diameters of membranes in such units range from 10 to 0.1 µm. Membrane elements can be both polymeric and ceramic. The main differences of ceramic membranes from polymeric ones are higher consumption of electricity of installations since higher output pumps are required, higher cost of membrane elements themselves which affects the overall cost of installations, but these features are compensated with longer service life of elements and the possibility to avoid using special cleaning solutions. In addition, polymeric membranes are characterized by lower costs and lower energy consumption of facilities, which reduces the initial investment, and a higher degree of thickening is possible with polymeric membranes.

2. Ultrafiltration

The ultrafiltration process takes place at medium pressure. The pore size of ultrafiltration membrane elements ranges from 0.1 to 0.001 microns.

Ultrafiltration is designed for standardization of milk in terms of protein, lactose reduction, production of whey protein concentrate and protein isolates, milk pre-thickening for cheese and curds production as well as for production of filtrational curd.

Ultrafiltration plants enable a more efficient use of milk and the components it contains, which increases the yield of the product. For example, when using milk pre-thickening units in front of the cheese or curd producers, it is possible to increase their productivity by almost a quarter and thus significantly save the working space of the company.

By adjusting the degree of thickening of raw materials, which can be not only milk (both whole and skimmed), but also prepared milk mixtures, such as curd collé, a whole line of innovative products can be developed, which will easily win the hearts of consumers and allow the company to make additional profit.

3. Nanofiltration

Nanofiltration units use membranes with pore sizes ranging from 1-2 nm. Typically in the dairy industry, nanofiltration units are used to concentrate and/or partially demineralize whey. While the applications for sweet, or whey, are quite broad, the use of curd, or sour whey, in its natural form, is quite difficult. To broaden the applications of curd whey, it is demineralized, i.e. the salts are partially removed. The level of whey demineralization can be conventionally divided into a number of segments with different types of dairy products as the measuring scale. Minimal degree of demineralization is up to 30%, whereas demineralization up to 70% enables to use such whey in the whole production range of adult food, and 90% demineralization gives a company a chance to use the whey in baby food. The pores of nanofiltration membranes allow monovalent salts to pass through, which, when dealing with curd whey, makes it possible to achieve a demineralization level of 25%, which, depending on the requirements and production program of the enterprise, makes it possible either to reduce the size of electrodialysis units installed further, or refuse to use them at all.

4. Reverse osmosis

Reverse osmosis membranes retain virtually all solids, allowing only water to pass. The membrane only partially allows low molecular weight components such as organic acids and nitrogenous compound components to pass, especially when they are neutrally charged. Reverse osmosis units require the highest pressure of all membrane units.

The pore size of the membrane elements is 1 to 0.1 nm. In the dairy industry, reverse osmosis units have several typical applications. First is the purification of whey permeate after a nanofiltration unit. In this case the unit is called a polysher and the water thus obtained is used to carry out a CIP of the unit itself. A second typical application is the thickening of milk (both whole and skimmed) for transport over long distances to reduce logistics costs. In this case, the milk is thickened by a factor of three, allowing the use of one milk truck instead of three. Reverse osmosis plants are also used on lactose production lines. Of course, everyone knows that reverse osmosis is used for water purification, but it should be noted here that differently designed units are used for water treatment.

5. Microparticulation

Microparticulation is used to further process whey protein concentrate. The basis of the microparticulation process is the thermal effect on the basic whey proteins. Under the influence of temperature the whey proteins are denatured and aggregated. They are then mechanically processed to give the adhesions of the proteins the shape and size of fat globules.

Visually, the process looks like the transformation of water into wine. The brown colored liquid becomes bright white, acquiring a rich, creamy taste. There are many applications for microparticulate. First of all it is low-fat products, which can include cheeses, yoghurts, fermented dairy drinks, cottage cheese products, ice cream.

What are the disadvantages of these systems?

The problem is that the microparticulation units that were used until recently had a rather large internal volume due to the fact that the heat treatment and the mechanical shaping of the protein agglomerates were performed sequentially. This process was accompanied by substantial product losses and also resulted in a rather low level of whey protein transfer into the particulate material. In addition, the viscosity limitations of the incoming raw materials and the low, up to 77° C, temperature effect really imposed considerable limits on the spread of these units. and they could not cope with a dry matter content of up to 50%. In addition, it was not possible to achieve the EcoProt+ micro-particulation system, which was developed by Kieselmann. This new generation of micro-particulation systems allows for simultaneous thermal and mechanical treatment, which drastically reduces the internal unit volume to just a few liters, increases the protein-to-particulate ratio to more than 80%, and provides for temperatures of 90 to 120 degrees Celsius. It is this unit that really, truly removes the restrictions on the application range of the particulet, as it avoids the problems with high bacteria concentrations that arise when whey is thickened. Sterilized parcikulat places no restrictions on the shelf life of the products made with it.

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