The yeast removal process usually requires the addition of diatomaceous earth into the fermented wine. This attracts the yeast cells to form clumps that remain in suspension. The resultant slurry is then pumped through the filter press by the Verderflex unit leaving the wine ready for bottling.
From the yeast flurry storage vessel, the slurry is fed into the peristaltic pump via a 32mm suction line made form flexible Verderflex hose to reduce pulsation. The pump is naturally fitted with stainless steel sanitary connections and its drive system includes a 1.1kW gear reducer to provide a pump speed of 48 rpm. This delivers 800 litres of the slurry to the filter press per hour.
On the discharge side of the filter press pump a 32mm flexible hose is used to feed the chamber filter press. Elimination of pump pulsation is even more important in this process so a 20 litre capacity air dome is also incorporated to absorb any excess. The dome also acts as a pressurised storage tank for the filter.
The chamber filters are evenly filled with the wine/yeast mixture to a pressure of 10 bar. As this pressure must be maintained and not exceeded for effective operation a pressure sensor is installed on top of the air dome. When 10 bar is reached the pressing shoes of the pump stop rotating, however at least one pressing shoe is always positioned to be fully compressing the hose. This maintains pressure in both the air dome and chamber filter and eliminates the need for non-return valves.
As the wine slowly flows through the filter, the pressure inside the air dome reduces, until the sensor registers a pressure of 7 bar. At this point the Verderflex pump resumes operation and continues to stop and start, maintaining an even pressure of between 7 and 10 bar until the filter is completely filled with yeast solids.
At the end of batch, when the yeast slurry feed vessel is empty, the Verderflex can run dry without damage. Or, if the filter is blocked in the middle of the batch the hose pump can be switched to reverse to empty the filter and air dome of yeast slurry, leaving the filter dry, so the yeast cake can be removed.
As the Verderflex VF25 is self-priming, the yeast product can be taken from the storage vessel even if this is below the filter unit. This provides increased application flexibility. A further major benefit of this pump for this hygiene-conscious task is that no moving part is exposed to the liquid stream. Indeed the hose is the only component that comes into contact with the wine and also the sole wearing part.