Winemaking Comes In From the Cold
by Tim Patterson
Oh, those irritating, crunchy little crystals. They’re called “wine diamonds,” but they’re about as welcome as bird droppings. They’re the potassium bitartrates that fall out of solution in wine at the least opportune moments—in the consumer’s refrigerator, just before the gala dinner party.
These little shards of cast-off acidity are, of course, odorless, tasteless and entirely harmless. Their sensory impact in the glass is much less significant than that of the sludge that can be found in older red wines—though oddly enough, unpleasant red muck gets treated as some kind of badge of honor. But because consumers apparently get quite freaked at the sight of tartrate deposits, winemakers go to a lot of trouble to get rid of them—not just in the white wines that routinely get chilled before drinking, but in millions of gallons of mass-market reds, which also often spend time in the fridge.
For decades, the only sure solution was cold stabilization, chilling wine down near the freezing point for a week or two, getting the precipitation over within the winery and using enormous amounts of electricity in the process. Other tartrate compounds could be added to help in seeding the process of forming and raining crystals, and that was about it. The past few years, however, have brought two waves of alternative treatments, both the result of fancy high technology: sophisticated forms of membrane filtration that remove the troublesome chemical components (including electrodialysis and other methods), and additive products based on yeast mannoproteins or organic cellulose that disrupt crystal formation.
Compared to traditional chilling, all of these approaches take less stuff out of wine and have smaller effects on organoleptic properties. In other words, we have another instance in which advanced technology comes to the aid of more natural winemaking.
From Montrâchet to mannoproteins
For winemaking’s first several thousand years (up until about World War II), there were two solutions available for the issue of bitartrate precipitation—although no one called it that.) Winemakers could simply ignore the deposits, figuring that having a few flakes in your flagon was a small price to pay for having wine at all. Alternately, if your winery had no heating, no insulation and freezing winters—what might be called the Burgundy model—nature could clean up wine’s act with no electricity needed. Either way, no effort had to be expended by the winemaker.
Observers noticed along the way that barrel-aged wines, especially those with lees in the mix, showed fewer crunchers in the bottle or glass. The immediate benefit of this self-stabilization was that the layer of cream of tartar could be scraped out of barrels and put to other uses. Centuries later, this association of dead yeast and fewer granules inspired research into the mannoprotein products now on the market.
Once the industry moved into the stainless steel-glycol jacket era, cold stabilization by bulk chilling in tanks became the norm, getting any potential precipitates out of solution in the winery, before they could materialize in home refrigerators and restaurant stemware. The method was quite effective, getting rid of nearly any level of potassium bitartrate instability and handling the somewhat less common but equally annoying calcium bitartrate issues at the same time. A sigh of relief was heard throughout the land.
But bulk chilling has several drawbacks, all of which have become harder to dismiss over time, and all of which have provided impetus for the development of alternative approaches. At the most basic level, cold stabilization involves a loss of wine—as much as 5% of the volume; as in any kind of fining, the gunk removed by the process swims in a bit of perfectly good wine at the bottom of the tank, which gets chucked out, too. The cost of lost wine, however, pales in comparison with the cost of the electricity devoured in holding wine at a freezing temperature for a couple weeks. According to Jose Santos, president of Enartis Vinquiry, it was the staggering electrical bills that led the producers of Champagne to launch the research that developed carboxymethyl cellulose (CMC) products, one of the new classes of tartrate stabilizers.
Of increasing importance as world wine standards rise are the ways in which cold stabilization can affect wine quality. By forcing a portion of a wine’s tartaric acid to engage in crystal formation and subsequently drop out of solution, chilling can, to varying degrees, lower acidity and raise pH. This not only changes the wine’s chemical balance but its sensory balance (its perceived acidity) as well. There is both anecdotal and research evidence that the expunged crystals take other things with them, from aromatic compounds to pigment. Finally, holding wine for extended periods at borderline freezing temperatures increases the chances of oxidation, since oxygen dissolves into solution much more easily at colder temperatures.
All in all, cold stabilization through bulk chilling is a very blunt instrument, exchanging at least some level of loss in wine quality for the removal of a purely cosmetic problem. Sooner or later, somebody was bound to build a better tartrate trap, and the past half-dozen years have produced several alternatives. Rather than treating the formation of tartrate crystals as an unavoidable problem better dealt with sooner than later, the new approaches strive to keep the precipitation-grade crystals from forming or growing in the first place, which means less stuff has to be taken out of the wine in order to achieve stability—more technology, more natural wine.
Potassium removal strategies
The first strategy to reach the market, starting about a decade ago in Europe, centers on preventing the formation of potassium bitartrate crystals by getting rid of the potassium. The first entry here was a process called electrodialysis, developed in France by Eurodia and the French national Agronomic Research Institute and later introduced in the United States by WineSecrets, which offers the rather expensive machinery for sale as well as providing mobile services. WineSecrets has dubbed its equipment STARS—for Selective Tartrate Removal System.
Wine to be treated makes a single cross-flow pass using a series of polymer membranes that separate potentially de-stabilizing ions—potassium, calcium, tartrate salts, etc.—with the help of a low-amper age electrical current. Unlike bulk chilling, which can noticeably reduce tartaric acid content, electrodialysis barely lowers that needle, instead removing the building blocks of future crystals before they get built. Put another way, electrodialysis removes material from wine, but not nearly as much as chilling and forced precipitation does. Analysis and monitoring of wine composition before and during the process gives much more precise control over the removal of potential instabilities. A variant of the process is used for simple pH reduction in certain red wines for which tartrate stabilization is less of an issue.
Another filtration-based approach is reflected in the technologies utilized by Mavrik and VA Filtration. (Their respective systems have significant differences deep under the hood, but the broad line of attack is similar.) With this technology, wine to be treated passes across a membrane, which keeps all the good stuff (the retentate) out and lets the problematic stuff (the permeate) through, including in this particular application potassium ions. The permeate is then run through a charged resin that yanks out the potassium, and the cleansed permeate is then reunited with the retentate. The result: same wine, no change to the tartaric acid content, just less potassium, and thus less potential for crystal formation.
A different school of stabilization focuses on preventing the growth of crystals to the point that they are likely to precipitate, removing nothing from the wine but adding in one or another substance that gums up the crystal formation works.
The sexiest entries in this division are mannoprotein products, derived from yeast and optimized to do what lees in barrel aging have always done. Laffort’s Mannostab and Oenobrand’s Claristar (distributed in the U.S. by Gusmer) are based on different yeast strains, use different extraction methods and rely on different fractions of mannoproteins; one comes dry and needs rehydration, and one comes in liquid form, but both employ the same mechanism to stop crystal formation: macromolecules of the selected mannoproteins hamper the growth of certain crystal faces, altering the shape of the crystals and keeping them from becoming precipitation-worthy.
The material being added by these products is ultimately yeast, a substance that has been in every wine since before it was wine, so the addition can be construed as quite natural (and indeed as organically certified.) You might think of it as lees aging, only in a bag or a jar, precisely measured.
Carboxymethyl cellulose (CMC) provides an alternative monkey wrench to throw into the crystal formation machinery. Two CMC products, using cellulose derived from wood, are currently in limited, trial distribution in the U.S.: Enartis Vinquiry’s Cellogum and Laffort’s Celstab. CMC inhibits microcrystal nucleation and growth; it’s not quite the same chemistry as what mannoproteins do, but the results are similar. CMC products are not recommended for red wines, since their interaction with pigment can have unpleasant consequences.
Finally, all the major fermentation product suppliers offer stabilizing agents based on gum arabic, an extract of acacia tree sap. While the main selling point of these products is their contribution to mouthfeel structure, masking tannins or preventing pigment precipitation, many of them also contribute to the crusade against unwanted bitartrate crystal formation.
Before we get to the fine print, one more advantage of the new waves of technologically driven alternatives to traditional cold stabilization: They all work much faster. The membrane filtration methods can process in a day the volume of wine that would need two weeks or more in tank; the mannoprotein and CMC additives can often just be tucked into the final steps of filtration and bottling. Faster processing also comes into play from an entirely different angle, particularly for red wines. Under economic pressure, many wineries have moved red production from barrels to tanks with oak chips or simply shortened times for barrel aging; as a result, the natural processes of lees contact and gradual tartrate precipitation don’t have time to play out, leading to an increased need for red wine stabilization.
All these technologies and products originally were developed in Europe, where all of them are approved by the relevant regulatory bodies for everyday use. The picture in the U.S. is more complicated, with things in various stages of scrutiny and approval by the FDA or the TTB. WineSecrets’ STARS electrodialysis is fully approved; Mavrik offers its stabilization services in the U.S., but VA Filtration currently only performs this work in Chile and Australia, pending clarification of certain issues with the TTB. The mannoprotein products have TTB approval, while the CMC products are in an earlier experimental stage. In five years, all of this will be readily available; for the moment, check with your supplier.
Pricing of these products and services varies both with the volume of wine being treated and with the level of tartrate instability that has to be dealt with. Cost comparisons quickly get convoluted, with differences showing up in the amount of testing and monitoring required, how many people need to be involved doing what, electricity rate fluctuations, and so on. But for a ballpark figure, all of the “filtration” methodologies and both of the mannoprotein products work out to around 25 cents per gallon; the CMC products, with more limited applications, are quite a bit cheaper.
None of these alternatives to traditional cold stabilization runs on autopilot—just turn on the machine or open the jug. All require careful analysis before and after to estimate the degree of potential instability and how thoroughly it has been dealt with. (On the testing side of its business, Enartis Vinquiry has developed a new wine analysis panel, an alternative to standard electrical conductivity testing that calculates the amount of bitartrate reduction needed and how that will affect pH and acidity.) Using either the filtration technologies or the additive products, attention has to be paid to timing, filterability of the wine before and after and other processing details. By comparison, simply putting a batch of wine in a tank and chilling it for two weeks is downright simple.
And—I know you were waiting for this part—none of these alternatives is a magic bullet that is foolproof and suitable for all occasions. As with anything else in Winedom, the effectiveness of a given treatment depends on the unique composition of the wine in question. CMC products present complications for red wines, requiring either a different product or separate treatments to stabilize pigment. Oenobrands recommends Claristar for white and pink wines, and it is working on a variation for reds. While the mannoproteins work well to prevent potassium bitartrate problems, they do not address calcium tartrates, which can rise to problematic levels in wines that go through deacidification.
Jose Santos of Enartis Vinquiry offered some useful perspective. There are, he noted, lots of wineries out there with substantial capital investment in chillable tanks, and expecting them to simply jettison the old ways tomorrow is unrealistic. In many cases, the best solution to the tartrate problem is not a single treatment but a combination: chill wine for a few days, for example, to knock out some of the tartrates, then disable the rest with a CMC/gum arabic product; or do the main work with electrodialysis, then add a pinch of a crystal disrupter just before bottling as insurance.
As always, nothing is simple, but sensory trials and anecdotal testimony from winemakers suggest the new waves of tartrate fixes do less damage to wines, validating the underlying chemical story, which is that less stuff is being taken out than by the old wave. The products and methods may not seem quite as “natural” as those freezing yet romantic caves in Burgundy, but the wines are more intact.
Tim Patterson is the author of “Home Winemaking for Dummies.” He writes about wine and makes his own in Berkeley, Calif. Years of experience as a journalist, combined with a contrarian streak, make him interested in getting to the bottom of wine stories, casting a critical eye on conventional wisdom in the process.
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