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Unformatted text preview: UNIVERSITY OF CALIFORNIA Department of Viticulture and Enology VEN 135 WINE TECHNOLOGY AND WINERY SYSTEMS 14. FILTRATION INTRODUCTION Filtration as applied to winemaking is a very general operation which encompasses a wide range of conditions from the partial removal of large suspended solids (approximately 10-100 m in diameter, grape pulp,bitartrate crystals or some of the yeast) by various grades of diatomaceous earth (D.E.) or filter sheets to the complete retention of microbes (approximately 0.5-1.0 m diameter) by perpendicular-flow polymer membranes. The terms "rough", "polish", "tight" or "sterile" will often be used to distinguish the openness (or alternatively, the porosity) of the filter medium. This openness determines the nature of the material collected from the juice or wine and also affects the resistance to flow and therefore the throughput of a filter unit. Figure 14.1 gives an overview of the types of filtration commonly used in the wine and other related industries. Filters can be classified according to their porosity, the nature of the filter medium, the method of housing the filter medium or the arrangement of the fluid flow path. Examples of the first four classifications would be "rough" versus "sterile", "pad" versus "D.E.", "plate and frame" versus "pressure leaf." For fluid flow, two types of classifications are used, perpendicular flow arrangements (also known as normal flow or dead end filtration) which are in common use in the wine industry and tangential flow filtration (TFF; also known as crossflow filtration) whose uses range from the sterile filtration of juices and wines to the removal of solutes such proteins (in "ultrafiltration" or UF) or the modification of composition such as ethanol removal (in "reverse osmosis" or RO). A final distinction or classification for filtration is the mechanism of action for the filtration. All filtration can be classified as either depth filtration or membrane filtration. Micrographs of examples of these two types of filters can be found in Figure 14.2. A depth filter works by adjusting the concentration of fibers or filtration particles so 1 10-4 10-3 10-2 10-1 1 10 10 2 P a r t i c l e S i z e ( m i c r o n s ) Conventional Particle Filters (DE, Pads) Microporous Filters (microfiltration, membranes) Ultrafiltration (specific molecule size, MWCO) RO (ionic/charged molecules) Pulp/Dust Bentonite/Proteins Yeast/Bacteria Figure 14.1. Four types of filtration. This is a classification based on the size of the particle being removed and the inherentflux capacity of the methods. that the probability becomes high that a particle moving through the filter bed will hit and stick to one of them. The actual distance between any two fibers or filter particles may be significantly greater than the size of particles being filtered out, but the overall density of these fibers is great enough to assure, to a high probability, that the desired filtration will occur. will occur....
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- Spring '09