On a recent Friday night I met a special friend for dinner at one of my favorite restaurants. Earlier I had gladly offered to bring the wine, and being familiar with the menu, I wanted to find that perfect wine that would pair well with most dishes. I spent some time going through my wine “stash” to pick a bottle that would fit the occasion and the menu. I decided on a 2004 Merlot from the Napa Valley.
When my friend and I were seated at the restaurant, I asked our server to open the bottle and decant the wine. As the server began to open the bottle, I found myself apologizing in advance to my friend just in case the wine had gone bad. I watched in anticipation as the bottle was opened, the cork was passed to me, and a small sample poured into my glass. I took a deep breath, paused, and proceeded to swirl my glass.
The aromas were wonderful, with tastes of lush deep cherry and dark berry, fantastic from start to lingering velvet finish. I was so relieved and excited to offer this wine to my friend. My nervous anticipation stemmed from a previous experience, not too many weeks before, when I met some out-of-town friends for dinner and, as in this case, I brought the wine. The bottle was a 2001 Knight’s Valley Cabernet that was also a well thought-out choice. My excitement and anticipation were dashed when the aroma indicated and the taste confirmed that the wine was oxidized.
More oxygen flaws than TCA
Results from the 2010 International Wine Challenge (IWC) competition in Britain show that the judges identified faults in 5.6% of all the wines tasted. The IWC is an annual two-week competition with more than 10,000 wine entries from around the world judged by hundreds of winemakers, wine writers and merchants. Looking at the 2010 statistics in “Results from the International Wine Challenge,”, let’s consider 10,000 bottles of wine tasted and of these 5.6% (560 bottles) had faults. Of those 560 bottles, nearly 55% (308 bottles) were flawed due to poor oxygen management (sulfides and oxidation). In comparison, 21% (117 bottles) were flawed due to cork taint (TCA).
If the wines averaged $100 per bottle at retail, the monetary loss due to poor oxygen management would be $30,800 compared to $11,700 for loss due to TCA. In this scenario poor oxygen management is responsible for nearly 64% higher loss than TCA. The losses are significant regardless of the price per bottle, and in the premium and ultra-premium arena they can add up to tens of thousands of dollars per year.
In addition to the monetary and consumer confidence losses, consider the questions that winemakers will need to deal with to determine the causes of improper oxygen management and correct them. Winemaker Steve Reeder, vice president and general manager of Simi Winery in Healdsburg, Calif., said, “The key to any wine is at the time of consumption. That’s when you want the harmony of aroma and structure to deliver to the consumer.”
Oxygen management and winemaking
Oxygen management has troubled winemakers for years. They have employed new methods, equipment and products to reduce oxidation (too much oxygen in the wine) and flaws from reduction (not enough oxygen) in wine. For each varietal, and sometimes varietal appellation, there is a different equation for how best to control oxygen and allow the wine to show its best varietal characters.
Regardless of winery size, winemakers strive to reduce and hopefully eliminate oxygen flaws. Smaller wineries are striving to identify and eliminate the gross causes of oxygen exposure, while larger wineries have met those goals and are fine-tuning their winemaking, maturation, bottling and bottle-aging protocols to maximize their efforts and achieve optimum oxygen management.
I spoke with winemaker Sig Yeilding, owner of the small family winery Yeilding Wine in Laytonville, Calif. Yeilding’s 500 to 600 cases of wine per year consist of several different varieties. When asked about his methods of oxygen management, he said, “What I am mostly doing is trying to limit and minimize my wines’ oxygen exposure from cold soak all the way to bottling. We have invested in upgrading our barrel room and our production room so that we can more easily maintain constant cool temperature and humidity.” He added, “I’ve been able to schedule my racking, knowing when I’ll most likely have an inch or so of headspace.”
Veteran winemaker Thomas Peffer of Napa, Calif., said, “For red wine, the most important time to introduce oxygen is just after fermentation. The splash rack allows not only the release of reductive gasses but also the absorption of oxygen. The oxygen starts the polymerization of polyphenols, stabilizing the color and evolving the flavor.”
Peffer cautions that wine movements are of great concern. “When the wine is moving, that’s where unwanted oxygen pick-up can happen. SOPs (standard operating procedures) that employ nitrogen sparge with all movements also strip out positive varietal attributes—not good. Preventing leaks that cause oxygen pick-up is better.”
When asked what he thought the biggest challenges were in achieving optimal oxygen management, Peffer replied, “It seems to me that the low levels of oxygen diffusion in oak barrels and cork stoppers, and the ability of current technology to measure this event, has led to an oversimplification by some to deny that it occurs. I look forward to more sensitive lab equipment and studies that will address this mystery.”
Simi Winery produces approximately 400,000 cases of wine per year. Some of the wines are meant for consumption shortly after bottling, but Simi Reserve wines are created for bottle aging. Winemaker Steve Reeder looks at oxygen as a tool to craft his wines.
“Oxygen is very important to wine in many stages of its life. To have a monitoring system that can measure oxygen at these various stages would give the winemaker more information from which they may be better suited to make decisions that affect the overall quality of the wine,” he said. “If I was given a report that showed me the wet chemistry and the oxygen level of each lot every time it is topped, racked, filtered, before and after the process, then that information could eventually lead to a new and/or better way to handle the wine. It would be another tool and could give the winemaker more knowledge of oxygen uptake, disposition and how it affects th e quality of the wine.”
Bottling and beyond
Optimum oxygen management needs to be maintained throughout the winemaking process from harvest to bottling. If wine does not reach the bottling line with proper oxygen levels, all the care that went into its development can be negated even before bottling.
“The biggest increase to the overall quality of the wines I’ve made over the past 34 years came when I started monitoring oxygen levels at the time of bottling,” Reeder said.
Bottling is the crowning event. Months or years taking care of a wine end when that closure is put in place—or so many think. The amount of oxygen dissolved in wine (DO) and oxygen in the headspace of the bottle (HO) as well as the type of closure chosen and storage environment have a large impact on the results in the bottle. With new studies coming in from all over the world concerning oxidative and reductive faults, more and more proof is being gathered showing how proper oxygen management during the stages of bottling and bottle aging are pivotal to improving quality and increased shelf life.
Dr. Elizabeth Waters of the Australian Wine Research Institute (AWRI), Dr. Rainer Jung from the Geisenheim Research Center in Germany and Dr. Stéphane Vidal, global enology director at Nomacorc, Belgium, were global research partners with a nonprofit consortium titled Oxygen in Wines or O2
W. Though the association has now disbanded, its research results are only now being digested by the international winemaking community.
Malcolm Thompson, global vice president of marketing and innovation for Nomacorc, explained how the research data was handled by the research partners and the O2
W: “Each individual academic institution retains the rights of publishing the research, which we believed was important to ensure the credibility of the research. Each research institution pursues its own publication in academic, peer-reviewed journals.”
DO + HO = TPO
W determined through its studies is that total package oxygen (TPO), which is the sum of the DO and HO, can determine shelf life, ergo quality, especially in wines slated for early consumption and highly reductive wines. With findings such as those from the International Wine Challenge showing that TPO may cause more flawed wine bottles than the more-publicized TCA, this new three-letter acronym may become part of every winemaker’s vocabulary.
As we know, wines bottled with high DO can quickly deteriorate, reducing quality. It seems to be the general consensus that bottling specifications normally are set at a post-bottle DO of <1 to 2 ppm (mg/L) depending on the varietal. The new information is telling us that we have to be concerned with DO, but HO may be a greater problem. A bottled wine with a measured DO rate that is within specifications may have a high HO, resulting in a high TPO that is very much out of the set specifications.
The free sulfur dioxide (FSO2
) in the wine is reduced by its reaction with the oxygen, which can leave the wine unprotected from microbial growth and further oxygen exposure. If you consider the O2
W findings that the HO in many cases can be 60% to 70% of the TPO, you could see that an HO in the range of 2 to 4 ppm or greater is possible. To reduce 1 ppm of oxygen requires approximately 4 ppm of FSO2
. If prior to bottling you have a FSO2
of 28 ppm, the post-bottle analysis is showing a DO of 1 ppm, and you can measure the HO at 2 ppm, your TPO would be 3 ppm. It will take 12 ppm FSO2
to react with the 3 ppm of oxygen, reducing the FSO2
to 16 ppm in the bottle, which may leave the wine vulnerable.
Keeping this in mind, you also need to consider the oxygen transfer rate (OTR) of the closure you have chosen to use. OTR is the amount of oxygen that can be transferred into the wine through the closure. OTR has been shown by the O2
W to have a significant impact on the development of red wine aroma in the bottle during aging/storage. This slow, continuous transfer of oxygen oxidizes phenolic compounds resulting in increased color stability and better mouthfeel. Reducing TPO at bottling and using gradual oxidation through closure OTR can enhance red wine. Screwcaps are an example of the lowest level OTR, while natural cork closures are among the highest.
Nomacorc, being interested in the findings pertaining to the effects of oxygen exposure through closure OTR on red wine during bottle-aging, worked closely with another research partner of the O2W, Dr. Véronique Cheynier of the Institut National de la Recherche Agronomique (INRA) in Montpellier, France. The INRA has been exploring the evolution of red wine aroma profiles, in particular red berry fruit attributes using Grenache wines at varying OTRs. The wines showed an increase in red berry fruit attributes as the OTR rate on the closure increased up to a point. These results indicate that the future may hold the possibility to choose a closure to best suit your particular varietal. In fact, Nomacorc is already producing closures with measurable OTR and continues to improve their designs.
Quantification of oxygen
Most wineries have monitored DO for years using a variety of reliable oxygen meters with submersible probes that can be dropped into a bottle or placed in-line. The meters use the Clark-type electrode to measure the DO. The electrode consists of a cathode and an anode submersed in an electrolyte. When the electrode is placed in the wine, the oxygen enters the sensor through a permeable membrane via diffusion; there it is reduced by the cathode, creating an electrical current that is then measured.
Measuring HO and OTR poses an entirely different problem: How can you take measurements of DO, HO or OTR in a closed bottle or system and not be invasive? A new type of oxygen meter has been developed to do just that, measuring the oxygen without opening a bottle, container or any closed system. This technological advancement has given researchers and winemakers the ability to quantify oxygen content regardless of the container. Several companies such as Nestle, Heineken, and Danisco use this technology in the food and beverage industry.
The technology is called oxo luminescence and is based on the effect of dynamic luminescence quenching by molecular oxygen. In short, a pulsing light source is generated, and the absorpti on of the light is measured and used as a reference. The same light is passed via a fiber optic wand through a luminescent sensor “dot” placed on the glass surface. The light transmitted through the dot collides with the oxygen molecule where energy transfer takes place and results in the reduction of the luminescent signal. The drop of the luminescent signal is compared to the reference measurement, and the difference indicates the amount of oxygen present in either the liquid or air space measured.
Several companies are currently producing analyzers using luminescent technology for various applications: Thermo Scientific–Orion, YSI, Hach-Lange, Precision Sensing GmbH and Nomacorc, to name a few. Precision Sensing, maker of PreSens, has collaborated with Nomacorc, allowing the company to use the PreSens technology to develop and market the NomaSense analyzer, according to Thompson.
Mai Nygaard, manager of NomaSense, provided me with these specifications: “Accuracy for the NomaSense using our standard sensor (PSt3) is as follows:
At high concentrations (atmospheric oxygen) in O2
%: +/- 0.2%, or in ppm (mg/L): +/- 0.09
At low oxygen concentrations in O2
%: +/-0.03%, and in ppm (mg/L): +/- 0.01.
“The repeatability has been documented to be 0.10% or 0.04 ppm, and the sensors show no cross sensitivity to other gases,” Nygaard continued. “The method has been validated according to OIV standards by Nomacorc’s research.”
Nygaard also reported, “Regional industry standards are being developed as well as internal standards by wine producers and retailers. In support of this important work and, based on global TPO benchmarking studies, Nomacorc has introduced a guideline for TPO values, categorizing into low, medium and high TPO.”
These TPO categories are:
• Low/well-controlled bottling: 1-2 ppm
• Medium/average bottling: 2-4 ppm
• High/uncontrolled bottling: 4-8 ppm
Oxygen management from harvest to that all-important first taste by the consumer is paramount to every winery. Development of these new technologies opens up a plethora of applications within a winery, bottling line and storage facilities. With continued innovations and research, our understanding of oxygen in wine and our ability to have the tools to monitor and manage oxygen will keep us moving along the road to perfection.
Jean L. Jacobson is a consulting winemaker in Sonoma County, Calif., a writer and author of “Introduction to Wine Laboratory Practices and Procedures,” a book published by Springer Publishing. Jacobson has 15 years of experience in winemaking.
Gordon, Jim. “What Oxygen Research Means to Winemakers,” Wines & Vines News Headline, Sept. 19, 2011.
Goode, Jamie. “Post-Bottling Winemaking” Wines & Vines August 2010 issue.
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