The role of membranes during cross-flow filtration
In the production of beverages such as wine, milk and, in some cases, fruit juices, filtration is often a crucial step in the production process. In these cases, before bottling, beverages must be filtered to remove sediments, impurities and unwanted substances that can alter the taste, appearance and quality of the finished product. Among the most advanced and productive technologies in this field are cross-flow filters, which we have already discussed in a previous article. These filters offer high efficiency and versatility, adapting to the different needs of the beverage industry.
Crossflow filters, however, are not all the same and can be customised according to the specific processing they have to perform. They use different types of filter membranes, selected according to the size of the particles to be removed, the viscosity of the liquid and other key factors. In this article, we will delve into the details of the filter membranes used in cross-flow filtration, exploring how they work, what their characteristics are and how they are selected. We will also add some practical examples, illustrating how these membranes are applied in real-life situations in the beverage industry, highlighting their importance in the production of high quality products.
TANGENTIAL MEMBRANE FILTRATION: THE DIMENSIONS
It is essential to understand the different configurations a filter membrane can have, as these directly influence its properties and functionality. Membrane configurations may vary depending on its composition, which may be organic, inorganic or a combination of both.
Furthermore, its size can vary, which determines its porosity and, consequently, the selectivity of the filtration process. These configurations can then be translated into a variety of filtration technologies, including the microfiltration, ultrafiltration, nanofiltration and reverse osmosis.
Some systems may also use specific membranes for the filtration of specific particles. In this article, we will examine each of these technologies in more detail, highlighting their applications.
The filtration of heavy particles
Cross-flow filtration is a revolutionary method for removing heavy sediments from beverages such as wines, vinegars and juices.
These machines use high-porosity cross-flow filtration applied to high-speed rotating discs, preventing clogging and allowing effective self-cleaning of the membranes. The result is a high quality filtrate that can be bottled directly, with no colour reduction and no oxygen absorption.
Its versatility and efficiency make it a viable alternative to vacuum filtration systems and filter presses, especially for the filtration of must and wine sediments.
MEMBRANES FOR TANGENTIAL MICROFILTRATION
Microfiltration membranes have pore sizes usually between 0.1 and 10 micrometres. They become crucial in sectors such as oenology, where they help preserve the clarity and integrity of wine.
The careful choice of membrane pore size is critical to achieving the specific objectives of each sector, while ensuring that the product’s distinctive characteristics are maintained.
Tangential Ultrafiltration: Applications and Membranes
Tangential ultrafiltration has essentially one difference to microfiltration: the porosity of its filter membrane, with pore sizes between 0.001 and 0.1 micrometres.
This specific pore size makes cross-flow ultrafiltration suitable for the separation of minor molecules, such as proteins and polysaccharides.
Specifically, the food industry can, for example, use cross-flow ultrafiltration to concentrate or fractionate proteins while keeping their nutritional elements intact.
For example, this occurs in the dairy industry in the production of the Whey supplement. In this case, you want the milk protein to remain concentrated in the retentate so that the product can be prepared while the milk flows through the pores of the membrane.
In this 60-second video, we can better understand the formation of the retentate:
An advantage of ultrafiltration is the operation at low pressures, which means less membrane wear and reduced energy costs.
In addition, the tangential nature of the flow helps minimise the problem of membrane fouling, increasing efficiency and process life. Ultrafiltration therefore proves to be an essential technology for many industrial applications requiring separation at the molecular level.
Here is an example of ultrafiltration.
MEMBRANES FOR NANOFILTRATION
Tangential nanofiltration uses membranes with pore sizes between 1 and 10 nanometres, offering an intermediate solution between ultrafiltration and reverse osmosis.
In the food industry, nanofiltration has found significant applications due to its ability to selectively separate small organic molecules and ions.
It is frequently used for the demineralisation of whey, allowing the controlled removal of salts while preserving proteins and sugars.
In the fruit juice industry, it can be used to concentrate natural sugars without affecting organoleptic properties.
If required, nanofiltration can be finely adjusted through the manipulation of variables such as pressure and temperature, allowing precise separation and the ability to adapt to different food products. Requiring pressure above 40 bar, nanofiltration is not usually used in oenology.
Its flexibility and precision make it an indispensable technology for high quality products in the modern food industry.
REVERSE OSMOSIS MEMBRANES
Reverse osmosis is a separation process that uses semi-permeable membranes to remove ions, molecules and larger particles from liquid solutions.
Unlike natural osmosis, reverse osmosis requires the application of pressure to overcome the osmotic pressure of the solution and push the solvent through the filter membrane.
In these applications, the membrane pores are less than a nanometre in size, allowing reverse osmosis to retain virtually all dissolved substances, including salts and heavy metals.
In the food industry, osmosis membranes are used for the concentration of fruit juices and the removal of impurities, keeping the organoleptic characteristics of the product intact.
In addition, reverse osmosis is essential in the production of pure water for sensitive applications. Although reverse osmosis requires high pressures and has associated energy costs, its ability to provide almost complete purification makes it an irreplaceable technology in many industrial applications, contributing to the quality and efficiency of production processes.
A WIDE RANGE OF MEMBRANES FOR BEVERAGE FILTRATION
The variety and precision of filter membranes in the beverage industry highlight the complexity of the cross-flow filtration process. As we have seen, from microfiltration to reverse osmosis, membranes are carefully selected according to the specific requirements of each product, allowing the removal of impurities and the preservation of desired product characteristics.
Appropriate advice and continuous development of processes related to filter membranes is essential to ensure high quality beverages while managing costs in this crucial sector of the food industry.
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