Issue link: http://winesandvines.uberflip.com/i/766392
64 WINES&VINES January 2017 VIEWPOINT bine it. The higher pressure your machine, the smaller the percentage you can work with. Tartrate fouling is important too, especially at high concentrations like 32° Brix. How do we get the most out of nice, tight RO membranes? With dry wine, pump pres- sure has to overcome an osmotic differential of only about 175 psi (12 bars), so a 70-bar system gives twice the flow of a 40-bar system. I am a high-pressure guy. Oppo- nents talk about shear forces associated with 1,000 psi systems, but in tens of thou- sands of trials, I have never seen any valid- ity to this concern. Wine systems are much different from de- signs for water. Because permeate flow is a small percentage of feed flow, you can string a large number of membranes in series without losing much crossflow scrubbing in the tail-end membrane. Consequently, small ROs with two to four elements are not very efficient. High- pressure systems fitted out with tight mem- branes can handle 12 to 16 membranes in series with little drop in efficiency. Same pump and controls. Why not? Adding filters is an affordable way to get more for your buck. You should also rig for overnight, unattended operation using a prop- erly designed fail-safe loss-prevention system that can double your throughput. Sometimes you just want to work on one barrel of your $200-per-bottle Reserve from grapes that the birds liked as much as you did. That means you need a shunt so you can re- plumb for one or two membranes when you rehabilitate your little darling. My life in reverse Since my divestiture of the service business in 2008, I have had no financial connection to RO equipment sales or production services. But ever since the Benzigers at Glen Ellen Winery chained me quite reluctantly to an RO machine in 1990, I have been pioneering its application in winemaking. Bruno Benziger had a dream to market a good-tasting, non-alcoholic wine, a project I explored for three years in the early 1990s. Although eventually aborted, the project gave me a window on wine's mysteries such as colloidal structure, aromatic integration and sweet spots. It also led to the develop- ment of VA-reduction and alcohol-adjust- ment patents and the 1992 founding of the wine technology service firm, Vinovation Inc. to exploit these inventions. Vinovation processed about 4,000 volatile acidity jobs in its 17-year history. More than 100 of these were subsequently named in Wine Spectator's Top 100 Wines of the World. We achieved this level of quality by using exclu- sively tight membranes with an MW cutoff of 80 daltons. It seems that today's expectations are lower (a wine getting a VA haircut is ex- pected to take a quality hit). I believe the primary factor in the process's sliding reputa- tion is the use of looser filters to make cheaper, faster machines. That said, 80-dalton membranes are not the right choice for applications where pas- sage of a larger MW taint is required. In these applications, quality loss is a neces- sary evil as in fining. Porosities of more than 150 daltons may be useful in juice concen- tration, but they are of questionable utility and legality in wine. Getting the membrane right The Benzigers' machine was built by Milli- pore and contained membranes made for producing drinking water from seawater. Like most RO membranes, these were spiral- wound cylinders containing a very high de- gree of surface area (see "RO is a Cross-Flow Technology"). These were spiral-wound seawater membranes that worked fine for salt rejection but turned out to have a low manufacturing standard. When (so-called) nano-filtration mem- branes came on the market in 1995, Vinovation eagerly stocked up on the new, improved membranes that were indeed better built and gave great flow rates. Early in 1996, I got a panicked phone call, jumped in my car and drove six hours south only to confirm that we had com- pletely ruined a batch of Central Coast es- tate Chardonnay with these overly porous membranes that had stripped its flavor and body. We went on an exhaustive hunt for a replacement membrane, ultimately pairing up with Osmonics, a division of G.E., which developed a hand-rolled polyamide mem- brane with the acid and amino sides re- versed that became known as the Vinocon RO5 and remains the industry standard. (See "GE Vinocon R05 Characteristics.") Ions such as acetate and lactate do not pass because they are hydrated by water and have functional molecular weights of several hundred. For this reason, SO 2 , which is almost entirely ionized, is largely con- served as well. GE went on to develop two other mem- branes with looser porosities. The Vinocon RO1 is used for removal of Brett character and smoke taint, which don't pass at acceptable rates in a tight RO membrane. Unlike the Vinocon RO5, the deployment of a Vinocon RO1 entails a loss of flavor and body similar in severity to a fining agent. GE also includes its Vinopro nanofilters in its wine offerings. This is not an RO mem- brane but instead graduates up in porosity to the nanofiltration range. The purpose of a nanofiltration membrane is to separate mono- and divalent ions, so it needs to be loose enough to deplete acid ions such as bimalate and bitartrate. These membranes strip acidity. I have seen dozens of jobs run on these membranes where titratable acidity (TA) is cut in half and pH shifted up a whole point to more than 4.5. High-porosity membranes improve perme- ate flow but also strip flavor. The Vinopro nanofilter series is, in my opinion, too porous for use on wine, though it may be a reasonable choice for juice concentration and flavored non-alcoholic wine where flavor retention is not an issue. Reverse osmosis equipment suppliers do not make membranes. They purchase and install them in the machines they sell, often repackaged under proprietary names that conceal their identities. Yet at least one RO manufacturer refuses to reveal the identity and characteristics of the membranes it in- stalls in its machines. A spokesman explained to me that without this protection of propri- etary expertise, customers would be able to purchase replacement membranes directly from suppliers, eliminating the middle man who provided the know-how, and also en- abling competitors to copy their designs. Beyond pore size, membrane specificity can get pretty exotic and include features such as GE VINOCON RO5 CHARACTERISTICS Molecular Weight (MW) Passage H 2 O 18 100% EtOH 46 80% Acetic acid 60 60% EtOAc 86 40% Lactic acid* 90 39% Malic acid 134 >1% Tartaric acid 150 >1% * Only molecular lactic acid passes based on its acid dissociation constant of 3.8. GE MEMBRANES COMPARED GE Osmonics Model Porosity Na + rejection Mg 2+ rejection Vinocon RO5 80 daltons 99.2% Vinocon RO1 120 daltons 98.5% Vinopro Series 150–300 daltons Passes readily 90% The porosity of GE Membranes makes them variable in applications from removal of Brett character and smoke taint to fining and nano-filtration.