It’s no overstatement to say that dairy products have been part of Kenneth Sjöström’s life since birth. The Tetra Pak dairy process engineer grew up on a farm and as a child helped to milk cows and collect milk for the local dairy.
“You could say I’ve lived and worked with milk and yoghurt for half a century,” says Kenneth, a Tetra Pak veteran of 25 years. He shares his specialty of yoghurt processing with colleague Katarina Lindgren.
A Tetra Pak dairy technologist since 2011, Katarina focuses on yoghurt and other fermented dairy products like cultured sour milk, quark and kefir. She and Kenneth help customers to produce top-quality yoghurt and to overcome the distinctive processing challenges associated with yoghurt production.
Processing experts Kenneth Sjöström, Katarina Lindgren and Carin Cronstrom
“Yoghurt is a very dynamic category and also a challenging one in terms of dairy engineering,” Kenneth says. “Strict food hygiene demands, and yoghurt’s variable viscosity, require specialist processing knowledge to get a high-quality product through the plant and into the package.”
Then there’s the diverse nature of yoghurt itself. Yoghurt varies not only in taste and type but also in when people consume it, how they consume it, and what they perceive its nutritional benefits to be.
“In Europe and North America, yoghurt is eaten mainly for breakfast or as a snack,” Katarina says. “In Asian markets like China it is consumed on the go or as a snack, often as a drink. In some countries – India and Pakistan, for example – it is primarily a cooking ingredient or food condiment.”
Yoghurt is also ever-changing. Once, consumers typically chose between plain or strawberry. Today, supermarket refrigerators are overflowing with possibilities as new formulations and tastes enter the market.
Based at Tetra Pak’s headquarters in Lund, Kenneth and Katarina work on yoghurt-related projects all over the world. They see three top challenges that producers must confront when planning their lines and configuring their production.
The first challenge is production consistency. All producers want their product to have consistent quality. It is vital to treat all the yoghurt in a line in the same way to guarantee the same final-product characteristics within and between batches.
“Many types of yoghurt require gentle treatment. The process of pumping, cooling and agitating a fermented product can damage its structure,” Kenneth says. “You need the same treatment for all yoghurt and a layout with the same piping arrangement for all product batches.”
Inadequate process control is another potential source of product inconsistency. The solution is effective automation and accurate temperature and pressure control throughout the process.
Katarina adds: “If raw materials and processing parameters are consistent and the physical layout of the line is consistent, then we will get a consistent end-product.”
She points out that inconsistent processing parameters can cause separation, variable viscosity, graininess and flavour variations in the final product.
The second challenge is plant flexibility. Modern yoghurt production requires the capability to produce a multitude of different flavours and formulations – from standard yoghurt with different fat levels to organic and lactose-free varieties, and from plain products to ones with fruit and cereal particles and even spices.
“You need to be able to change between different product recipes, and all switches result in some product being lost,” Kenneth says. “Knowledge of the product and the production process is crucial to minimise losses.”
He adds: “We need to analyse the different types of yoghurt a producer wants to produce and also to imagine what yoghurts they might want to produce in the future. Ideally, we want to design a line that can do everything the customer wants today and also possibly something more.”
Some producers choose to divide their production into two lines – one high-volume and one with smaller volumes – but it all depends on what you produce.
“A single line is a cheaper investment, but it might not be cheaper overall because of losses when switching,” Kenneth says.
Another yoghurt processing challenge is cost-efficiency. In this context, the emphasis is on cost-effective production. Katarina and Kenneth explain that there are several ways to ensure that a yoghurt line is efficiently configured.
One is to avoid over-specifying the line. The objective is to get exactly the right process and equipment design that can handle desired production scope with an element of future-proofing.
Learning the individual characteristics of each formulation is critical to designing the right line, Katarina explains. “We design lines that are fit for the customer’s purpose.”
A customized line also allows the producer to make the most of its raw material. Optimizing the process design can enhance viscosity preservation, thereby allowing the producer to use fewer or other ingredients.
One way to achieve this is for customers to visit the Tetra Pak Product Development Centre, where they can refine and verify their recipes with support from Tetra Pak food technologists.
"Learning the individual characteristics of each formulation is critical to designing the right line,” Katarina explains. “We design lines that are fit for the customer’s purpose.”
Ultimately, this is about delivering a cost-effective solution and helping the customer to spend wisely. “Why install ‘standard’ yoghurt equipment that uses the biggest pumps, tanks and agitators when you can achieve the desired product quality with better-tailored equipment?” Katarina asks.
Then there are operating costs. Yoghurt production is energy-intensive because it involves a lot of heating and cooling.
Kenneth advises choosing an equipment supplier that knows how to optimise energy consumption and how to build energy recovery systems to reuse the heat used, for example, in plant cleaning.
“There’s no one magic piece of equipment for this. What you need is knowledge of process design and heat recovery systems and how energy can be transferred between different parts of the plant,” Kenneth says. “This is an area where quite significant savings can be made if you have the know-how.”