​​​​​​​​​​​​​​​​​​​​​​​​Precision pasteurization – your path to perfect yoghurt

​A yoghurt milk pasteurizer is the foundation of yoghurt processing. Its precise control of temperature is critical to achieving yoghurt’s unique taste and mouthfeel.

The pasteurizer’s heat treatment plays a key role in determining yoghurt structure. Heating denatures proteins in the yoghurt milk, changing their physical structure and enabling the milk to deliver yoghurt’s characteristically thicker texture.

“The pasteurizer is a central piece of equipment in your yoghurt line because it’s responsible for making the milk ready for the fermentation phase,” says Mikael Lövquist, a senior Tetra Pak specialist in heating and pasteurization.

Temperature’s crucial role

For protein denaturation, he adds, the pasteurizer must operate at the right temperature and hold the milk for the right length of time. “Total control over temperature and holding time is essential.”

The long holding time required for yoghurt milk, typically five minutes, is achieved with a specially designed spiral holding cell, covered with insulation and stainless-steel cladding.

Temperature precision is paramount not only for pasteurization itself, but also for the effective operation of associated process steps, such as deaeration, homogenization and fermentation.

Air in yoghurt milk has a negative impact on yoghurt quality and is removed from the milk by vacuum in a deaerator. This process depends on incoming milk having a consistent inlet temperature. If the temperature is too high, the deaerator’s vacuum will lead to an unwanted increase in heating demand and hence operating cost.

Also, if the temperature is too high for the condenser to handle, excess vapour may leave the product, raising the risk of product loss. Conversely, if the incoming temperature is too low, insufficient air may be removed. The worst-case scenario is foaming that fills the deaerator vessel, disrupting production.

Heat variation and product quality

Further processing steps such as homogenization and fermentation also rely on exact temperature control for best results. If homogenization temperature is not controlled, certain additives – such as starch – may be damaged and not provide the right benefits for the final yoghurt.

Yoghurt cultures typically have a very narrow temperature spectrum for optimal growth. Any variation can impact the yoghurt’s taste, acidity, viscosity and stability.

For yoghurt, a fermentation temperature of 43°C is often preferred as most yoghurt bacteria grow best at this temperature. Sometimes a degree or so lower or higher may be required to achieve different product quality or fermentation time. Hence, temperature regulation must be ultra-precise.

“Tetra Pak yoghurt pasteurisers are designed so you can set exactly the right temperature for your pasteurization, homogenization and deaeration, and the outlet temperature to the fermentation tank,” says Mikael Lövquist.

Minimize product losses

Running cost is another prime consideration in yoghurt production. Tetra Pak Pasteurizers come with a low-loss balance tank that minimizes the mix of product and water during the pasteurizer start-up phase.

“A double action of filling the balance tank and the pasteurizer at the same time allows the balance tank to be virtually empty of water, before you start filling the unit with product,” Lövquist explains.

The same mechanism is used when emptying the unit, using water to push out the final drops of yoghurt milk.

Compared to common designs using traditional filling or emptying, the Tetra Pak yoghurt pasteurizer has a clear advantage. Savings depend on production volume, but the Tetra Pak design can reduce mixed phase losses by 68 percent.

Opportunities to save energy

Tetra Pak yoghurt pasteurizers also offer a range of energy-saving features. In hibernation mode they can reduce steam use by 60 percent during water circulation, while waiting for production to start. This saving is achieved by reducing flow, turning off pressure in the homogenizer and pausing the cooling water supply. Hibernation mode takes only a couple of minutes to activate and deactivate, making it easy and efficient to use in short periods of water circulation.

Yoghurt pasteurizers are also designed for optimal heat regeneration. Heat recovery can be as high as 93 percent when producing set yoghurt. For other yoghurt types, the scope for heat recovery is often more limited due to the process, with high outlet temperature.

To further minimize the losses in production time and product, Tetra Pak pasteurizers offer a hot divert system with double seat security. This system reacts to insufficient pasteurization time and temperature by diverting product before it enters the long holding cell. This means that it is possible to restart production safely – without CIP and disinfection – after a brief temperature or flow fault. In instances where steam supply is unstable, this can save many hours of lost production time and avoid thousands of litres of product going to waste.

Maximum uptime is achieved by extending the pressing depth of the pasteurizer’s heat exchanger plates, increasing the area inside the plate to enable longer running time. 

Versatility and total process control

Tetra Pak pasteurizers are also uniquely versatile, allowing you to produce different products and temperature programs in the same unit.

All Tetra Pak pasteurizers come with a high level of automation and easy integration with your plant management system, giving operators a full overview of the process and hence total process control.

“We use intuitive automation to allow the pasteurizer to run both consumption milk and yoghurt milk, even though a lower pasteurization temperature is used for standard milk pasteurization where protein denaturation is not desired,” Lövquist explains.
When changing from consumption milk to yoghurt milk, automatic valves are used to bypass the Tetra Pak Separator and Tetra Pak Standardization unit, which are typically included in consumption milk production. At the same time, the yoghurt milk configuration of the pasteurizer will automatically connect a spiral holding cell and control the outlet temperature with a warm outlet temperature configuration.

“A multi-duty pasteurizer design is really useful for dairies that produce many different products and in small batches,” Lövquist says. “And if you run larger volumes you can still run this setup and enjoy full flexibility.”​​