Wine reverse osmosis

In hot-climate viticulture it is a common practice to lower the high ethanol content of wines made from overripe fruit by partial dealcoholisation. This objective can be achieved by vacuum distillation, where the spinning cone column technique allows even more viscous liquids to be processed. Alternatively, a water-ethanol fraction can be separated from wine by reverse osmosis, followed by distillation of the water-ethanol permeate to yield high-grade ethanol and pure water. The latter will be added back to the treated wine. 

Other methods to achieve bitartrate stability, rarely used in the North Coast, are addition of metatartaric acid, electrodialysis, reverse osmosis, and ion exchange. Concern with potential bitartrate instability varies from winery to winery. Some enologists prefer to keep the processing of wine to a minimum. They rely solely on cool fermentation and winter storage temperatures to precipitate excess bitartrates. They trust their customers will overlook any additional bitartrate crystals that precipitate out in bottled wines. 

Fermentation temperature and fermentor design can induce evaporative alcohol losses but these are relatively small. Based on current state of knowledge, choice of yeast and fermentation conditions constrain wine style and do not provide a reliable approach for achieving at least a one percent or greater loss of potential alcohol content of wine (Boulton et al. 1998 de Barros Lopes et al. 2003 Palacios et al. 2007). Several physical techniques, such as spinning-cone and reverse osmosis, and nanofiltration can be used to remove sufficient sugar or alcohol for the production of reduced or low alcohol products (Ferrarini et al. 2008 Grosser 2008). 

Electrodialysis is a well-proven technology with a multitude of systems operating worldwide. In Europe and Japan, electrodialysis dominates as a desalting process with total plant capacity exceeding that of reverse osmosis and distillation [3]. Electrodialysis with monopolar membranes is applied to different food systems, to demineralization of whey [5-8], organic acids [9], and sugar [10,11], separation of amino acids [12] and blood treatments [13], wine stabilization [14—16], fruit juice deacidification [17-19], and separation of proteins [20-22]. These applications use the sole property of dilution-concentration of monopolar lEMs in a stack of as many as 300 in an electrodialysis cell. 

In this paper preliminary experimental results obtained in a University-Industry joint research project are reported. The tests have been carried out in cooperation with a medium size well known winery. The aim was to analyze the potential of ultr filtration and reverse osmosis in solving some of the problems or in improving the existing technology in wine making. A diagram of the potential of pressure driven membranes in must treatment is presented in fig.l. 

Synthetic membranes with calibrated pores are used for various operations in the wine industry ultrafiltration, front-end microfiltration, tangential microfiltration and reverse osmosis. Electrodialysis and pervaporation, special separation techniques described elsewhere in this book (Section 12.5.1), also make use of membranes. 

In reverse osmosis, an external excess pressure is exerted upon the side of the concentrated solution that is higher than the osmotic pressure posm of this solution. This causes the solvent s molecules to be forced in the direction opposite to the osmotic effect. They are forced through the semipermeable membrane and into the more diluted solution where they are enriched. This procedure is used in desahni-zation of water as well as wine processing. 

Membrane electrolysis cells have many applications in the food industry (dairy, wine, fruit juice, etc.), water softening, purification or recovering effluents from electroplating and other chemical processes. Possibly the best known processes are desalinating brackish water with a moderate salt content (other processes such as reverse osmosis are used upstream) and demineralising whey in the dairy industry. 

Membrane processes in must and wine treatment separation techniques involved in wine technology include membrane processes. Pressure-driven membranes (ultrafiltra-tion, reverse osmosis) play an important role in must and wine treatment and have solved some of the problems in traditional wine making technology. Various polymeric mon-branes of different configurations have been used in must stabilization. 

An important element in wine laboratories is the source of water to be used to prepare reagents. Due to varying amounts of chlorine or minerals, tap water should not he used to prepare reagents or for rinsing glassware. Rather, purified water is best for these purposes. Small distillation stills are available that provide distilled water necessary for most laboratory needs. Other systems produce deionized water, and there are some units that rely on reverse osmosis. As expected, costs vary widely but depend on the needed output of the system as well as the quality of the incoming water. 

Ugarte, P., E. Agosin, E. Bordeu, and J.I. Villalobos. 2005. Reduction of 4-ethylphenol and 4-ethylguaiacol concentration in red wines using reverse osmosis and adsorption. Am.J. Enol. Vitic. 56 30-36. 

Ultraflltration is also used to fractionate and concentrate proteins from potato processing wastewaters. Other protein wheys can be processed by reverse osmosis. Electrodialysis is used for a number of applications in the food and beverage industry, including deionization or deacidification of fruit juices, wines and, in the dairy industry, milk and whey. It often competes directly with ion exchange processes. 

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