Increased consumer demand for natural foods produced transparently is driving a trend towards minimal additive use. In yoghurt milk formulation, membrane filtration can allow producers to avoid the addition of milk powder, strengthening their ability to offer products with a more wholesome profile.
Greek yoghurt and other concentrated yoghurt products like quark, labneh and Icelandic skyr have served as a natural nutrition source for centuries. More recently, their high protein content, healthy image and pleasant fermented taste have elevated them to near-superfood status among health-conscious consumers.
Concentrated yoghurt products also double up as condiments in cooking – in sweet and savoury dishes alike. Quark and Greek yoghurt, for example, are widely used as ingredients for sauces and dips, as well as in desserts and pastries.
For dairy companies, this popularity creates scope to push farther and deeper into a growing segment. Increasingly, producers want the flexibility to produce a broad spectrum of products and capacities. From low-fat, high-protein to high-fat, medium-protein – and all combinations in between.
Concentration is a crucial production step when it comes to achieving these objectives. Different concentration technologies are available. One is ultrafiltration, a form of membrane filtration that offers a variety of advantages.
Claus Birkemose, Sales Manager at Tetra Pak, says that one of membrane filtration’s most eye-catching benefits is that it allows practically full protein retention.
“In membrane filtration, or more specifically ultrafiltration, the protein is retained in the product. Only lactose and mineral salts pass through the membrane; protein and fat stays in the concentrated product,” Birkemose says.
The high yield of ultrafiltration allows you to minimize your use of milk when producing your end product.
The beauty of membrane filtration is that you can produce a range of yoghurt varieties with different protein and fat contents. This is achieved by controlling the feed and output to the filter unit, which makes it possible to define the composition of the outgoing product.
For instance, feeding in 1,000 litres of semi-skimmed milk with 1.5 percent fat and 3 percent protein to a membrane filtration unit allows concentration to 300 litres of concentrated yoghurt with 10 percent protein and 5 percent fat. By regulating the output from the filter unit, you could alternatively achieve 500 litres of concentrated yoghurt with 6 percent protein and 3 percent fat.
“Membrane filtration allows you to produce a complete range of product types using a single filtration unit, from non-fat high protein yoghurt all the way to full-fat cream cheese,” Birkemose says. “Many of our customers like to make different products with different fat contents – that’s the market trend. Membrane filtration makes this easy to achieve.”
Using membrane filtration to concentrate yoghurt can also offer superior product quality thanks to a process that treats the product gently, enhancing the yoghurt’s texture and stability and resulting in a very smooth mouthfeel and shiny appearance.
Milk powder is often added in stirred and set yoghurt production to increase the protein level (also known as “dry matter”) of yoghurt milk. This is because higher protein content improves the yoghurt’s texture, viscosity and stability. When formulating yoghurt milk for stirred and set yoghurt, membrane filtration also enables producers to reduce or avoid the use of milk powder as an additive.
Ultrafiltration or reverse osmosis allows processors to remove water and thereby increase protein levels and dry matter using concentration. Ultrafiltration of yoghurt milk removes water, some salts and some lactose. Reverse osmosis removes water.
Both technologies allow producers to achieve their desired level of dry matter without having to use milk powder, in turn allowing them to claim a “cleaner label” with fewer additives.
Such a setup may allow the producer to eliminate a powder mixing station and storage room and mixing tanks from the line, delivering a further spin-off in the form of a smaller factory footprint.
Birkemose stresses the importance of working with a knowledgeable partner when producing multiple product varieties on the same line.
“At Tetra Pak we have around 75 membrane systems installed worldwide only for concentration of fermented milk applications,” he says. “We have conducted numerous in-house trials to investigate the impact of line design on product texture, mouthfeel, appearance, stability and taste, so we have a lot of knowledge about what’s important when it comes to getting the right taste and structure for each product. We work closely with customers to find the optimal line design and recipe to get the perfect outcome.”
Tetra Pak offers three types of filtration membranes: ceramic, spiral wound and plate and frame. All make great yoghurt but have different strengths. Which one to choose depends on several factors such as need for robustness, viscosity of the final product and focus on investment cost versus total cost of ownership.
Tests show that ceramic membranes offer the highest robustness and longest lifetime typically lasting for eight years or more. Spiral wound membranes, so called because they are rolled into a spiral, are cast on polypropylene support material and last for about a year. Plate and frame membranes, also made from polypropylene, are cut to fit the unit’s plate size. They also last for about 12 months.
Ceramic and plate and frame membranes can cope with the highest viscosities. The former can handle everything up to quark, while the latter can go beyond that and be used to make full-fat products.
Plate and frame membranes often offer the lowest total cost of ownership over their lifetime and are commonly preferred for high-viscous products such as quark because the alternative – a combination of spiral and plate and frame membranes – can be more complex to operate.
Investment cost is highest for ceramic membranes and lowest for spiral wound membranes.
Each customer case is carefully assessed before recommendations for the line design – including membrane types – are proposed.
It is worth noting that in any yoghurt line setup, one advantage of membrane filtration is that capacity can be increased later by simply adding new filtration loops or sections.