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WINEMAKING passes 50% of its constituents into the fil- trate (permeate). I pioneered the use of tight reverse os- mosis for the removal of volatile acidity. With a membrane MW cut-off of 80 dal- tons, only acetic acid passes into the per- meate, to be trapped by a resin prior to recombining with the retentate. The method takes advantage of the O molecule is a dipole attracted by the dozens to the charge on any ion, clinging like a gel layer that increases the ion's fact that ions are very large. The H2 functional molecular weight (FMW) by at least 500 daltons. The un-ionized acetic acid at 60 daltons will pass easily through an RO filter with an 80-dalton porosity, but its ionized acetate counter- part with a FMW of 600 daltons doesn't pass through at all. A precisely identical method may be used in de-acidification of excessively tart wines by employing looser RO mem- branes (near the 150-dalton legal limit) to pass malic acid at 134 MW. With a 150-dalton porosity, more flavor will be lost, but useful amounts of lactic and malic acids (pKas of 3.8 and 3.5, respec- tively) can be removed if the pHs are not too high. The new generation of membranes fo- cuses on membrane selectivity. Although the wine industry is tiny by global indus- trial standards, we are beginning to receive trickle-down benefits from other industries, and off-the-rack technologies frequently appear and improve our options. While RO membranes are impervious to ions, membranes have been developed that do just the opposite—ion-selective mem- branes that pass only the ions. Electrodi- alysis (patented by Eurodia and marketed in the United States as STARS), a method perfected some 20 years ago in France for economical and gentle cold stabilization, has been increasingly employed to great advantage for de-acidification. Treatments differ entirely for the two different causes of high pH/high TA. FRENCH OAK DOMINOS tween two membranes, a cation-perme- able membrane that will only pass H+ and Ca2+ and an anion-permeable mem- Caroline Hoogenboom Napa - Sonoma Cell. (707) 364-6334 caroline@ermitageusa.com Amy Lee Oregon - Washington Central coast of California Cell. (509) 995-2771 amy@ermitageusa.com Vincent Garry, Sales Director Cell. (707) 225-2105 vincent@ermitageusa.com In electrodialysis, wine is pumped be- , K+ brane that passes tartrate and malate ions. A low-voltage DC current propels ions through these membranes—cations gravitating to the negative pole and an- ions attracted to the positive pole. In ef- fect, KHTa is drawn into a brine that is discarded or sold. In de-acidifying the high-TA wines of recent cool years, neutralization with po- tassium or calcium carbonate is limited by rising pH. If followed by electrodialy- sis, pH can be brought back down while simultaneously removing K+ and Ca2+ to Office: Tel: (707) 224-2377 Fax: (707) 224-2390 433 Soscol Avenue Suite B151 Napa, California 94559 - USA 142 Wines & Vines JAnUARY 2012 prevent instability. The beauty of this method is that unlike conventional cold stabilization, it pro- tects the colloidal structure of the wine and saves a lot of energy. Electrodialysis can remove KHTa without the entrain- ment of colloids that accompanies crys- tal precipitation. Thus there is very little flavor stripping, and the method has been highly preferred to chilling by a trained sensory panel. When used in concert with tartaric acid addition, electrodialysis can often give you virtually any desired pH and TA. Since it requires high clarity, electrodialysis runs Parc d'act i v i tés des Ber t ranges - 58400 La Char i té- sur -Loi re - France Tel . + 33 3 86 69 43 79 | FAX + 33 3 86 69 67 47 | www. tonnel ler ie-ermi tage.com