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WINERY & VINEYARD EQUIPMENT June 2017 WINES&VINES 45 PRODUCT FOCUS Membrane Filtration Choosing the right system is a cost-effective way to clarify or remediate most wines By Richard Carey M embrane filtration has become a major factor in current winemak- ing production. Because of the breadth of the topic, this Product Focus about current uses of membranes for wine production will be broken into two parts. This first part reviews the major clas- sifications of membrane usage and their ef- ficacy in the wine-production process and includes a list of the companies that supply equipment. In the second part, we will pro- vide information about the different mem- brane companies and their specific equipment for use in the wine-production process. My first exposure to membrane technology took place in 1983 or 1984. Peter Meier from Millipore came to my winery in California to demonstrate the "greatest advent of high-tech equipment for the wine industry." He brought a demo unit to show me visually what mem- branes can do. We ran a recently fermented wine through his new device and got a drip, drip, drip of pristinely clear, wonderful wine out the delivery side of the filter. That event stimulated my continuing inter- est in this technology. Today membrane tech- nology has evolved and now covers a wide range of processes, from primary fermentation to molecular sieving of good and bad mole- cules in the almost finished wine. Membrane filtration is not quite at the magi- cal level in wine production, but it is not that far off. Consider the following: The device can clarify a recently fermented, racked wine to 0.2µ in one step. After that, the same technology can remove volatile acids, and then even remove the ethanol to a point where the "wine" pro- duced is alcohol-free. It is also possible to re- move selected compounds based on molecular size and, after that, select molecules based on hydrophobicity versus hydrophilicity. One of the more bizarre aspects of membrane technology is its ability to select compounds based upon their chiral orientation (two compounds that differ based upon their mirror image). The membranes can separate compounds over a wide range of molecular weights and charges. One can find companies such as VA Filtration, Pall and Koch Membranes that cover the whole gamut of membrane types, configurations and sizes of systems. There are also companies such as Oenodia (Stars elec- trodialysis/Bipolar), Romfil (microfiltration) or ATP Group (microfiltration) that specialize in one type of system. The basic membrane filtration process Membrane filtration is different from conventional diatomaceous earth (DE), pad or lenticular filters. The depth filtration model uses the depth of the filtration media. This model relies on the statistical chance that any molecule will pass through the filter's tortuous media path. Membranes use a horizontal flow path known as tangential flow filtration (TFF) or crossflow filtration. With this fundamental change in the architecture of the filter media, many winemaking processes can be improved and made much more selective. Membranes allow for a more precise pore size differentiation, so the different levels of product flow can provide the winemaker with choices, depending on the need for clarification or molecule segregation. The concept of TFF removes one of the biggest obstacles of depth filters—the entrapment of insoluble particles. Depth filters rely on the fibrous nature of the path to trap these particles in a gradation of the weave fibers through the filter, starting from coarse to fine from entry to exit. Interspersed are irregular particles such as DE that trap the wine's insoluble particles. Once the spaces are "trapped" (or clogged), the filter must be discarded. Product flow in membrane filtration is tangential to the membrane surface, which has defined pore spaces and provides a smooth surface on which the product (wine) can move rapidly. A combination of the insoluble parti- cles and the wine's velocity continuously scrubs the surface. Like a river, there is mass flow in the main body, and the liquid that is actually touching the membrane surface has zero flow. This zero-flow region is known as the gel layer. The main product flow space (the retentate) is subjected to pressure by the system's pumps, providing the tangential flow. The pressure and speed keeps the liquid and its particles moving, which allows the molecules that are smaller than the pores to pass through the gel layer to the permeate side of the membrane. Statisti- cally, more of the smallest molecules pass through in the beginning of the filtration cycle. This is one reason some people believe membrane filtration strips out flavor. Continu- ous tasting of the progress of a batch will show that as the batch progresses, more of the larger molecular weight particles will pass the gel layer to the permeate side, and the flavors of the wine improve. This means the higher the concentra- tion of the batch that can get through the mem- brane, the more the filter material replicates the original wine. This is an important criterion to judge the effectiveness of a filter's action. The holdup volume is comprised of the total volume