PERISTALTIC PUMPS FOR PUMPING YEAST

Peristaltic Pumps for Pumping Yeast

Why use a Verderflex peristaltic hose pump for pumping yeast in wineries.

Wine is made from grapes grown specifically for wine production. After harvesting, the grapes are transported to the winery, where they are crushed. The resulting grape juice, containing sugar, is fermented into an alcohol containing liquid by adding yeast. Once fermentation is complete and the sugar initially present in the grape juice has been converted into alcohol, the yeast must be removed and the clarified young wine can be further processed and aged to produce wine.

Red wine differs from white wine in the initial fermentation. To produce red wine, the grape juice is kept in contact with the grape skins, which impart the colour to the wine, while white wine is fermented from only the grape juice. Traditionally, fermentation utilised yeast that were present on the grape skin, giving the grapes a naturally powdery appearance and occurred in open top oak vats where the grape juice and skins were mixed by a daily pigeage (stomping). Conversion of the sugars into alcohol generally takes between 7 and 14 days. Leaving the fermentation up to uncharacterized yeast gives rise to variability in the wine, resulting in lost revenues for winemakers.

Today, to reproducibly create particular flavour profiles, winemakers have replaced this traditional fermentation process with a modern approach that, while recreating the environment necessary to produce alcohol from the grape juice sugar, seeks to control all aspects of fermentation to reduce variability. Stainless steel has replaced oak vats during fermentation and specific yeast strains are added to jump start fermentation, and provide winemakers with exquisite control over the flavour profiles of their wine.

Once fermentation is complete, the yeast must be removed to prevent them from imparting “off” flavours to the wine and to clarify the wine, resulting in its final crisp, clean appearance. Yeast removal is a two-step process. First, an agent is introduced (fining agent) that causes the yeast to stick together in large clumps, making them easier to remove. This suspension of yeast clumps and wine is then filtered to remove the yeast so that the clarified wine can be stored or bottled.

Verderflex’s peristaltic food grade pumps are ideal to provide the pressure required to process the wine/yeast slurry through a filter, removing the yeast from the wine. Some filters, especially manufactured for this purpose, come complete with a Verderflex peristaltic hose pump as an integral part of the system. In this case, the yeast/wine mixture is fed through a 32mm diameter flexible hose to the pump’s intake port. Flexibility in the intake line reduces pulsation from the peristaltic action of the pump. Pulsation is important to minimise as pulsation causes the yeast clumps to disintegrate and individual yeast cells to pass through the filter. Sanitary, stainless steel couplings reduce the intake tubing from 32mm to the 25mm tube used within the pump. A 1.1kW gear reducer drives the pump, resulting in a pump speed of 48 rpm. This translates into 800L/hr of process fluid delivered to the filter per hour. At the pump’s discharge, the 25mm hose pump is connected, again through the use of sanitary reducing couplings, to a 32mm diameter flexible hose that feeds the filter. Pulsation reduction is important on this side of the pump as well, as the yeast clumps have not yet been separated from the wine. In addition to the flexible hose, a 20L air chamber is installed between the pump discharge and the filter input. This air chamber’s function is two-fold. First it contributes to pulsation reduction and second, it acts as a pressurised storage tank for the filter.

An optimal filter pressure of between 7 and 10 bar is maintained by controlling the pump via a pressure sensor that is situated within the air chamber. When the pressure reaches 10 bar, the sensor sends a signal to stop the pump. As the liquid/yeast mixture slowly travels through the filter, the pressure drops and when the sensor reaches 7 bar, a signal is sent to start the Verderflex peristaltic pump. One critical feature of this configuration is that at least one shoe of the pump’s rotor is completely compressing the tube at any given time, to act as a valve, maintaining the pressure within the air chamber even in the absence of the pump’s rotation. The starting and stopping duty cycle of the pump is maintained until the filter is full of yeast or the process fluid is completely filtered. Verderflex hose pumps offer several advantages for this process. At the end of each run, when the yeast slurry has been completely fed into the filter, the pump can run dry without damage. Alternatively, if the filter clogs, the pump can be run in reverse to remove the unfiltered liquid and allow filter cleaning prior to completion of yeast removal. Finally, at the end of each wine-making season, the pump’s hose can be completely replaced with a new hose ready and sanitary for next season’s wine.

Advantages of Verderflex Hose pumps:

  • Peristaltic pumps are self priming, so position of the pump with respect to the slurry storage vessel is not important.
  • Peristaltic pumps provide constant flow at increasing pressures.
  • Only the hose contacts the wine, leading to easy cleaning and maintenance.
  • The hose is the only wearing part.
  • Pump can be run dry without damage.
  • Valves are integral to the pump, separate valves not required.

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