Inquiring Winemaker


There's No Substitute for SO2 (Yet)

August 2012
by Tim Patterson
Clearly, the most important ingredients in winemaking are the grapes, without which we’re left with fruit wine. The second most important is yeast, without which we just have grape juice. And a close third is sulfur dioxide, without which we might prefer settling for grape juice.

Sulfur dioxide, says Zack Scott of Scott Labs, is “a miracle chemical, so perfectly suited to wine, and it does so many things at the same time.” Grapes do one thing—ripen, at least most years; yeasts do two things—convert sugar to alcohol and (maybe) encourage aromatic compounds and precursors. SO2 does an amazing number of things: It kills unwanted and unpleasant microbes across several life-form kingdoms, combats the ravages of oxidation, binds up acetaldehydes (improving aroma), plays an important role in most winery sanitation regimens and dramatically improves the chances that a bottle of wine can survive worldwide transportation and years of shelf life. “It will be VERY hard to replace,” notes Michael Considine, a plant biology researcher at the University of Western Australia, “not least because it’s so cheap.”
    Using SO2 on grapes, not wine

    One of the most intriguing efforts in the “use less” department of SO2 management comes from the research of Michael Considine, a plant biology researcher at the University of Western Australia, who suggests that exposing grape berries to gaseous SO2 before fermentation can enhance the natural defenses built into the grapes, heightening the expression of genes that have “previously been shown to be involved in pathogen defense as well as tolerance to stress such as cold or low oxygen.”

    By implication, grapes can become more self-reliant by encountering SO2, without needing to put the SO2 in the wine. Alternatively, and better, Considine hopes to learn more about exactly how the self-defending gene expression is triggered, in hopes of identifying some other, less toxic way to provoke it.

But sulfur dioxide has its downsides and its detractors, too. In excessive amounts it can be dangerous to wine drinkers, and in smaller amounts it can be downright irritating, causing headaches, allergic reactions and so on. It can also be a workplace hazard if not handled carefully. Increasingly, the use of sulfur dioxide carries a kind of stigma in some quarters for not being “natural,” despite the fact that fermenting yeasts always create at least a little of it in their brief careers. Perhaps the unkindest cut of all comes from California State University, Fresno, enologist Ken Fugelsang, who observes that although sulfur dioxide does many things, it doesn’t do any of them particularly well: Its anti-microbial powers dissipate with high pH, and the anti-oxidant value varies wildly with wine composition.

Because of the downside, an entire industry has sprung up seeking to develop alternative materials and technologies to replace sulfur dioxide. Yet because SO2 is so versatile and effective, none of the substitutes have gotten much traction.

Just say no (more than necessary)
There are, of course, an increasing number of winemakers who stay away from SO2, or use it only in emergencies, and manage to make good wine year after year. (See “Wine: Natural, Natural Enough, and Sort of Natural” in the December 2011 issue of Wines & Vines.) With healthy fruit, scrupulous cleanliness and perhaps some tolerance for elevated VA, sulfur-free winemaking can indeed be successful. There is little chance, however, that this approach to winemaking will become mainstream, just as restaurants that only serve raw food will never replace steak houses.

In the mainstream, large numbers of winemakers are finding ways to use less sulfur (or no more than they absolutely have to.) Zack Scott observes, for example, that while the standard addition at the crusher used to be 50 parts per million (ppm) of SO2, lots of wineries now keep it down to something more like 20 ppm. Scott also notes the increased use of lysozyme at the crusher, which knocks back lactic acid bacteria, reducing the need for SO2 and putting malolactic fermentation on hold for a while, improving opportunities for early color binding. The quality of lab work has improved at many wineries, making sulfur additions evidence-based, not simply routine-based. This voluntary self-restraint is probably the biggest news in the world of sulfur dioxide alternatives: just use less.

Scott Labs also does a brisk business selling Velcorin, the trade name for dimethyldicarbonate (DMDC), a very effective anti-microbial agent that is entirely legal, highly toxic if mishandled and rarely discussed in public. Its main use is at bottling time, when it offers insurance against, among other things, a Brett bloom in the bottle; using Velcorin reduces the need for a final dosage with sulfur dioxide. While largely under the radar, Scott estimates that as many as 800 wineries in California use Velcorin from time to time.

Scott also mentioned the increased use of sulfur dioxide in granular or tablet form, rather than liquid or rehydrated powder. The advantage here is workplace safety: less pungent aroma, less need for masks or special ventilation or other preventive steps. This change in form does not result in less sulfur being put into wine, just in less exposure for staff in the winery.

Bob Kreisher at Mavrik North America added a couple of other high-tech approaches to lowering SO2 levels. In 2011, Mavrik got a call from a customer whose SO2 dosage regulator had malfunctioned, leaving behind several hundred parts of total SO2. Mavrik’s stock in trade is crossflow separation, so they came up with the right membrane and the right way to absorb both free and total SO2 from the permeate. While doser malfunctions aren’t likely to be a major business opportunity, Kreisher thinks there may be other uses, like controlling levels in export bulk wines, which can get elevated sulfites by passing through many hands on the way to market, or helping organic winemakers g et their SO2 levels down below the legal threshold of 10 ppm.

Kreisher’s other suggestion comes straight from basic wine chemistry: The lower a wine’s pH, the less SO2 is needed for stability. In high-pH wines, up around 4.0 or even higher, removing potassium (they’ve got a membrane for that) and bringing down the pH means less need for sulfur. Along these lines, Fugelsang says it all comes back to sanitation: The lower the populations of bad actors, the less damage they do and the easier they are to control.

And finally in the less-is-better category, ascorbic acid periodically comes and goes as a promising player. The theory goes that since ascorbic acid loves to devour molecular oxygen, it can supplement sulfur dioxide’s anti-oxidant role, allowing a reduced amount of SO2 to proceed with the anti-microbial mission. Unfortunately, in some circumstances ascorbic acid ends up promoting oxidation, not reining it in, making it more than a crapshoot as a sulfur replacement. Otherwise known as Vitamin C, ascorbic acid is no more a miracle cure in winemaking than in the battle against the common cold.

Alternative methods
Alongside these various strategies for using less sulfur dioxide in wine, efforts have been under way for several decades to find an alternative, some other compound or technology that would do sulfur dioxide’s job but without the negatives.

Fugelsang recalls when, about 25 years ago, he and fellow Fresno State professor Carlos Muller tried using carbon monoxide as an anti-microbial agent. It worked in bench trials, but as soon as they scaled it up, the method broke down. Fugelsang also had more than one run at using salicylic acid, a close relative of the active ingredient in aspirin, though again, it never performed as well on wine as it does in its major application: anti-acne treatments.

In 2008 there was a flurry of publicity about the publication in a technical journal of findings by a group of Greek enological researchers suggesting that an extract from black radishes, Raphanus niger, might provide the long-sought natural alternative. My Internet searches revealed hundreds of references to this news—all of them dating from 2008, and none since.

One strategy to progress a little further is ozone for disinfecting grapes and must as well as barrels and equipment. The Italian Purovino company has patented a protocol for use of gaseous and aqueous ozone during a number of stages in winemaking, and its website advertises successful trials with wines from the Marchese de Frescobaldi. Purovino USA representative Joe Hajost is currently scouting for U.S. wineries to partner with the company for commercial-scale trials.

Several other projects aim to replace the sulfur dioxide with one or another elemental physical forces capable of doing the anti-microbial dirty work. To begin with, the Australian Cavitus ultrasound system has been shown to do a superior job at barrel cleaning. The sound waves induce cavitation—pockets of bubbly gas—within liquids, blowing up microbes (excellent for killing Brettanomyces) and even clearing out tartrate deposits. So far, for reasons unclear to me, the technique has barely caught on after making a bit of a splash in demonstrations in California a few years ago.

Ultraviolet light has long been known to have anti-microbial powers, and the South African SurePure system has been slowly gaining adherents. First certified in 2010 for winemaking in South Africa, the technology is getting trials in Italy, Argentina and Australia, and it’s aiming for certification by the OIV in Europe and seeking commercial placements in the U.S., according to company representative and winemaker Neil Patterson. Multiple trials have indicated that the treatment does not otherwise negatively impact wine quality or composition.

A team of Italian researchers centered at the University of Molise is pursuing another strategy, the application of low-level electrical current. Several academic studies suggest that low electrical current (LEC) disrupts cell membranes and enzymatic activities in both yeast and bacteria, and during the course of several years, the researchers have learned a good deal about the effects of different levels of milliamperage and types of electrodes. Promising small-scale commercial experiments have been done with both the pre-fermentation phase, when LEC can clean out unwelcome critters, and with wine during aging, when Brett can be snuffed out. Microbiologist Giancarlo Ranalli, one of the lead researchers, indicated in an email that the group had obtained an Italian patent and was launching a spin-off to pursue commercialization of the methods.

Finally, another European effort focuses on the application of pressure to eliminate unauthorized critters. Rapidly increasing pressure on a confined liquid with inert gas, then rapidly removing the pressure, ruptures microbial cell walls. Theoretically, according to Ana Lucia Vasquez, project director for the PreserveWine consortium, the Pressure Change Technology (PCT) method can be used at any stage of winemaking, from clarifying juice to preparing for bottling. After some initial funding through the EU’s Eureka program, PCT is now being investigated by a host of partners from several European countries, with results due out this fall.

All these alternative technologies are still somewhere in the development phase, with the bugs in their bug-killing methods being slowly worked out. While all of them hold some promise as anti-microbial strategies, none directly deals with the anti-oxidant side of sulfur dioxide’s utility. And in compiling this survey of alternatives to SO2, I was struck by one other pattern: All the work—from black radish extract to electrical currents, from ultrasound to ozone—originated outside the U.S. In Europe, at least, the search for alternatives is driven by the knowledge that the EU will be steadily ratcheting down acceptable sulfite levels and ratcheting up the disclosure of sulfite content on wine labels.

Sooner or later, one or more of these avenues of investigation will pay off and lead to a combination of technologies and protocols that will be commercially significant. But since you are likely reading this in August, my advice as you prepare for the impending harvest is: Get your order in for sulfur dioxide.

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.

Currently no comments posted for this article.