Freeze Concentration: The Critical Role of Product Transport

Freeze concentration is considered a particularly gentle method for concentrating liquid foods. Without thermal stress, water is removed through controlled freezing, while flavors, vitamins, and sensitive ingredients remain in the liquid phase. In industrial practice, however, it becomes clear that it is not crystallization alone that determines the success of the process, but above all the controlled transport of the product between the individual process steps.

Crystallization as an intermediate step

Unlike thermal evaporation, water separation in freeze concentration occurs through the targeted formation of ice crystals. At temperatures below the freezing point, nearly pure water crystallizes out. The dissolved components remain in the concentrate.

The clear distinction between crystallization and concentration is essential here. Crystallization describes the physical process of ice formation. The actual concentration takes place only after the mechanical separation of the ice crystals, for example in wash columns or comparable separation stages. The final product remains in the liquid phase.

Since the process operates without heat, vacuum, or a vapor phase, highly volatile aroma components are preserved. At the same time, heat-sensitive proteins or enzymes are not denatured. The sensory similarity to the starting product is one of the main reasons for using freeze concentration in high-quality juices, coffee and tea extracts, wine, or dairy products.

Mechanical sensitivity in the process

As concentration increases, the flow behavior of the product changes significantly. Viscosity rises, temperature windows narrow, and delicate structures such as ice crystals, fruit particles, or protein-based aggregates form. These are sensitive to mechanical influences.

The transitions between individual process stages are particularly critical:

• the recirculation of ice slurries through heat exchangers,
• feeding into wash columns,
• and the recirculation of the concentrate within the plant.

Even moderate shear forces, local turbulence, or pressure fluctuations can damage crystals. This directly affects the separation characteristics in the downstream stage. Reduced crystal stability can lead to altered separation performance and thus to losses in yield or product quality.

Consequently, product transport becomes the focal point of process design. The type of conveying determines whether the benefits of freeze concentration are actually retained.

Requirements for pumping technology

Several criteria are decisive for the transport of sensitive media in freeze concentration:

• minimal shear stress,
• uniform, low-pulsation flow rate,
• stable pressure conditions,
• hygienic design with full cleanability.

Screw pumps with volumetric, chamber-by-chamber delivery meet these requirements particularly well. One example is a twin-screw pump such as the GEA Hilge NOVATWIN+, which is designed for hygienic applications involving sensitive media.

Two non-contacting rotating screws form closed pumping chambers in which the product is continuously transported. Local shear stresses are reduced, and pressure fluctuations are minimized. The wide speed range allows the pumping characteristics to be adapted to different product conditions. Low speeds enable particularly gentle product handling, while higher speeds can be used during cleaning operations.

Integration of product and CIP operations

In hygienic applications, cleanability plays a central role. Freeze-concentration plants often work with changing recipes and product batches. Accordingly, regular and reliable CIP processes are required.

In practice, screw pumps such as the GEA Hilge NOVATWIN+ are frequently used for this purpose, as they can handle both gentle product transfer at low speeds and CIP return at higher speeds.

Pumps capable of handling both product transfer and CIP return reduce the number of units required. This simplifies the system architecture, minimizes dead spaces, and can shorten downtime during product changes.

An EHEDG-compliant, low-dead-space design, as well as full CIP and SIP capability, are essential requirements. Additionally, design features such as front pull-out design facilitate maintenance and service.

Adaptability for different applications

The range of possible applications in freeze concentration is broad. Fruit juices with high Brix content, coffee extracts with elevated solids content, wine, or protein-based products each place different demands on viscosity, particle size, and temperature control.
Flexible adjustment of the conveying characteristics is therefore crucial. Different spindle geometries, varying speeds, and suitable sealing concepts enable precise design tailored to the respective product.

At the same time, operational efficiency is gaining importance in plant design. Sizing the conveying technology to meet specific needs can reduce material usage and energy consumption, thereby contributing to the overall plant’s cost-effectiveness.

Mechanics as a future factor

Trends such as clean label, plant-based formulations, or fermented intermediates further increase the demands on gentle mechanical processing. Complex matrices are sensitive to shear and pressure fluctuations. Mechanical stability is increasingly becoming a limiting factor in process design.

Freeze concentration exemplifies how closely thermodynamic and mechanical aspects are interlinked. Only when the conveying technology is tailored to the structural sensitivity of the product can the process be operated in a reproducible and economical manner.

Conclusion

Freeze concentration offers significant advantages for high-quality beverages and foods. However, its industrial implementation requires a holistic understanding of the process. In addition to crystallization itself, product transport plays a central role.

Conveying technology that minimizes shear stress, maintains stable pressure conditions, and meets hygienic requirements contributes significantly to process stability. Only through the interaction of all components does freeze concentration become a robust and controllable process.