Disc Stack Centrifuge for Pre-treatment of Berry Extract

Berries such as blueberry, blackberry, raspberry and cranberry are widely used in the extraction of natural pigments and functional food raw materials. After crushing, enzymolysis and solvent leaching, the feed liquid is heterogeneous, mixed with tiny plant cell fragments, insoluble fiber, denatured protein and sticky colloidal substances. If these fine impurities directly enter the ultrafiltration or ceramic membrane system, the membrane surface will quickly form a dense cake layer, resulting in sharp flux decline, frequent CIP cleaning and shortened membrane service life.

Traditional pretreatment methods include sedimentation and frame filtration. Sedimentation takes a long time and occupies large tank volume, and the separation effect is greatly affected by temperature and viscosity. Plate-and-frame filtration requires filter cloth and filter aids, which may adsorb anthocyanins and lead to loss of active ingredients. Besides, frequent cloth replacement increases labor cost and solid waste. Disc stack centrifuge, as a high-speed centrifugal separation device, realizes rapid phase separation by centrifugal force, which is very suitable for continuous online pretreatment of berry leaching liquid.

The core component of disc stack centrifuge is a set of stacked conical discs. When the machine runs at high speed, the feed liquid enters the disc gap. Under strong centrifugal force, solid particles with higher density move outward and deposit on the drum wall, while the light liquid phase containing anthocyanins and small-molecule polyphenols flows inward and discharges as clarified liquid. It can be designed as automatic slag discharge type. When the solid content accumulates to the set value, the drum opens automatically to discharge sludge without stopping the whole production line.

In the industrial berry extract process, the centrifuge is arranged before the membrane unit. The complete pretreatment combination is: leaching tank → basket filter → disc stack centrifuge → intermediate tank → membrane clarification system. The feeding speed, differential speed and slag discharge interval are adjusted according to the solid content of raw liquid. For berry water extract, the typical feeding solid content is 0.5%–3%. After centrifugation, most visible suspended solids are removed, and the turbidity of outlet liquid decreases obviously. It should be noted that the disc centrifuge cannot remove dissolved macromolecular colloids, so it cannot replace the membrane clarification step.

The outstanding advantages of disc stack centrifuge in berry processing are obvious. First, continuous high-speed separation, large single-machine throughput, suitable for industrial production of 1–10 m³/h. Second, the separation process is completed in a closed drum, short contact time with air, effectively reducing the oxidative degradation of anthocyanins. Third, no filter aid is added, less loss of active components, and the slag after discharge can be further dried to recover fiber. Fourth, compact structure, small footprint, easy to connect with the subsequent membrane system.

There are also applicable limitations that need attention. It is not good at separating ultra-fine colloids with density close to water. If the feed liquid has extremely high viscosity, the separation efficiency will drop. At this time, appropriate temperature rising or dilution is required. Regular maintenance includes lubricating oil replacement, disc cleaning and inspection of sealing components. After long-term operation, organic matter may deposit on the disc surface, so hot alkali circulation cleaning is required periodically.

This combined process of disc centrifuge + ceramic membrane / ultrafiltration has been widely adopted by many plant extract factories. Centrifuge undertakes the main solid removal task, greatly lowering the fouling pressure of membrane elements, extending the membrane service cycle and stabilizing the flux of the whole line. For anthocyanin products with high requirements on color value and clarity, this cascade separation scheme is more economical than using membrane alone.

To sum up, disc stack centrifuge is an indispensable pretreatment equipment for berry extract. It forms a complementary separation system with membrane technology, balances separation precision and production capacity, and helps extract enterprises obtain stable and high-quality berry clear liquid while reducing operation and maintenance costs.