Understanding Oxygen and Screw Caps

Bottling Line Decisions Affect Oxygen in Screw Cap-closed Wine More than OTR

“The moral of the story is: Screw caps are different. You pick the best closure for your specific wine and utilize your vendor’s expertise if you can,” said Cara Morrison, the Chardonnay winemaker for Sonoma-Cutrer Vineyards in the Russian River Valley, who has been studying the various screw cap closures for years now. She’s been running trials on liners with differing oxygen transfer rates (OTRs) and learning about proper screw cap application for the winery’s various Chardonnay brands.

Sonoma-Cutrer, which started testing screw caps in 1999 on its Reserve Chardonnay following issues with natural corks, moved to Saranex-lined screw caps in 2001. “We wanted to start at the top, if you’re going to make all that wine from all of your best vineyards, spending all that time and effort, you want it to be perfect. You don’t want any corked bottles at all,” she said.

Following more trials and test marketing through the years, Morrison said the winery kept its retail-focused wines in cork because consumers were not completely ready to pay more than $20 for a screw-capped wine. However, 60 percent of its production is under screw cap, including all on-premise wines, even the Pinot Noirs.

“Why screw cap? There’s no TCA. It saves money. You don’t have cork quality control testing, which is huge. Overall, the market acceptability is better but, again, there are still some challenges out there,” she said.

That’s not to say there aren’t some difficulties in maintaining and understanding screw caps. At Innovation + Quality 2017, Morrison led a panel and sensory trial that delved into managing oxygen in screw capped wine, from adapting winemaking techniques, bottling line quality control, proper application and oxygen transfer rates.

The panel argued that, while important, the OTR of the liner isn’t the only aspect of screw caps that affect the final wine. Morrison and Zoran Ljepovic were quick to point out that it might actually be bottling line performance that makes the most difference in total and perceived oxygen in in a wine.

Bottling Line Decisions and Quality Control

For 17 years, Zoran Ljepovic has been dealing with quality control at Constellation Brands, and today is the company’s director of quality control/quality assurance. He’s studied enology and viticulture at the University of Zagreb and spent eight years making wine in Croatia before moving to California to earn his Master’s degree in enology from Fresno State University.

“When you consider how much time we put in the vineyards to take care of the grapes to properly grow to get the right grapes, to properly pick them and crush them, process them, fermentation, aging, everything, we really don’t pay much attention to bottling, especially when talking from the winemaking point of view. I think winemakers get really tired. When it comes to bottling, they just kind of hand it off,” he said. This laissez-faire attitude is one of the worst things that could happen to a wine, according to Ljepovic, who provided a series of steps to manage quality on the bottling line.

First and foremost, the equipment must work properly. To keep every filler spout working correctly, regular maintenance must be completed. As not all screw cap heads will close appropriately, there will be some variation from one filler spout to another—and if you’re switching between closure types, like screw cap to cork and back again, the spouts need to be adjusted properly.

“If you don’t do that, you cannot blame anybody else or suppliers if you don’t have good results,” he said.

Once the line is working properly, Ljepovic stressed the importance of correctly measuring oxygen. When it comes finally to closing the bottle, the industry has been measuring dissolved oxygen (DO) for years and the meters have consistently been updated and improved and our understanding of oxygen pickup has grown. If the whole system has been properly purged, if there is no leakage anywhere, and if it’s a proper seal, the pickup shouldn’t be high. At Constellation, the team settles somewhere around 0.3 ppm as average pickup, according to Ljepovic, but it quite often ends up just 0.1 or 0.2. From there, he said, what we aren’t doing is measuring oxygen in the headspace.

The amount of oxygen will depend on the wine itself, as different wines have different abilities to bind oxygen. Verne Singleton published work stating that white wines can reach 8 to 10 saturations (one saturation is around 9 milligrams per liter). Red wines, on the other hand, with more tannins and phenolics, can reach 20 to 30 times that saturation, he wrote, making them more stable.

Ljepovic emphasized the need to measure both the dissolved oxygen and oxygen to reach Total Package Oxygen (TPO) or total measurable oxygen. “If you don’t measure, you have no idea what is happening,” he said.

Molly Longborg, assistant winemaker for Halter Ranch Winery in Paso Robles, uses the Stelvin Lux screw cap for the winery’s Rosé, Grenache Blanc, and Synthesis which is a price-point Cabernet Sauvignon blend. For her, the session was helpful in discovering quality control parameters and understanding of best practices. “Coming from a medium-sized winery, we do not always have the opportunity to run such in depth experiments on bottling QC, and I found it very insightful to learn some of the lessons/trials and tribulations that larger wineries have discovered. It is always nice when someone with the time, quantity of bottles, and proper resources can pass along the information they learned through arduous experiments in the hopes that other places can utilize and benefit from the conclusions,” she said.

Proper Screw Cap Application

Before any discussion on proper screw cap application, Morrison got a “little nerdy” and reviewed screw cap terminology.

There are a lot of different components to a screw cap, all of which need to be applied correctly. In that vein, a lot can also go wrong: new glass or faulty bottles can cause issues, the capper adjustment and pressure must be made appropriately and, of course, the screw cap itself must have been manufactured correctly and contain no faults.

“All three must be in alignment to work. If one element changes, the cap performance changes. You change vendors of screw cap. You have a different glass run. The capper is getting out of adjustment. You haven’t played with it in a while. All these things can change your performance so you have to check all these different things,” said Morrison.

Glass Finish Flaws

The glass sealing surface (the top of the bottle) requires a smooth finish in order to have the right pressure and the right seal. Any inconsistencies in the finish, any bumps or peels, will result in a liner that does not sit level with the bottle and no vacuum seal will be created.

Capping Setup and Calibration Flaws

“Ask your vendor for help,” said Morrison. “It’s what they all pretty much told me: ‘If people would have just called me first, we could’ve solved some problems and they wouldn’t have so much downtime.’ Or, if you have a really experienced person on the line that learns how to properly adjust the capper, make sure that you’re doing it on a regular basis.”

A number of issues can occur if you don’t have the right adjustments on your capper: spinning defects can cause it to not be tight enough, the threading is not visible or not in deep enough, broken bridges, cut threads and bird’s beak are all various problems if you don’t have the right alignment. After extensive discussions with vendors, she found that the overall consensus was that the proper threading is more important than the tuck-under because is most important in creating the perfect seal.

The threads take the pressure off the tuck-under, which locks the skirt into place, which is also important because if it’s not tucked in place, it can cause the entire screw cap to come off during consumer removal. When this happens, the hold is good and no oxygen is entering the wine, but it’s just not on properly. It also shows that you’re not pilfer-proof: it means anyone can open, and potentially taint, your wine.

Switched screw cap vendors recently? Each vendor and its products often have different heights for the bridge and the tuck-under bead. It could be off from your previous screw cap by a millimeter or less, but it will make a huge difference whether application is done well.

Oxygen Permeable Liners

Given that the bottling line has been adjusted properly, the cap was sufficiently applied and there are no other points of oxygen ingress, the last step in understanding oxygen and screw caps lies in the liner. Each vendor has its own product line, with differing OTR rates and methods to allow oxygen in. Morrison’s trial was conducted to see which would suit her wine best.

Varied OTR Sensory Trial Results

“We already know there’s a difference between the liners of tin and Saranex so we said, ‘Well, there are all these new ones in the market. We should test them out, see what’s what.’ The theory is that it’s a O2 consistent bottle. It takes down the bottle variation. Saranex is not always the same oxygen transfer rate, but these new screw caps are guaranteed to be the same oxygen transfer rate. There’s something to it, I think,” she said.

The Russian River Ranches Chardonnay is bottled under screw cap and Morrison wanted to test the various OTRs available to see which ingress rate is preferred. Chardonnay wines were tasted after 18 months of aging to see the effects of the screw caps.

The 2014 Russian River Ranches Chardonnay was bottled in the summer of 2015 under six different screw caps: The VinPerfect Light (0.11 ppm O2 per year or low permeability), VinPerfect Medium (0.21 ppm O2 per year or medium permeability), VinPerfect Medium Plus (0.49 ppm O2 per year or high permeability), and three screw caps from G3 Enterprises with high, medium and low post-bottling ingress rates.

One of the major differences between the two vendors’ lines is how they go about allowing oxygen in. Oxygen enters G3’s liner around the threading—VinPerfect’s allows oxygen to pass through the center of the liner. Each uses contrasting technologies, liners and layers.

“We’ve been tasting it over time and testing it, checking the O2 and SO2. We didn’t do the total package oxygen—I didn’t know about that until Zoran told me about it at Unified. We’ve noticed, basically, the SO2s have all gone down at the same rate regardless of closure. The DOs haven’t really changed much.”

But on a sensory level, she wanted to see how the different levels of O2 admission would affect the wine in terms of fruitiness, freshness and other important characteristics. Morrison and the winemaking team held in-house sensory analysis sessions and discussions, but also wanted feedback from her peers. This meant showing her wines to a group of ultra-premium winemakers.

For the session at IQ, half of the room tasted the three VinPerfect screw caps against a control (Saranex) and the other half tasted G3’s. No names were printed on any of the tasting sheets and each wine was given an alpha-numeric code to avoid bias.

To ensure the best possible sensory trial, she and the IQ team brought in Larry Brooks, consulting winemaker at Paraiso Winery. Brooks has spent close to four decades making fine wine in California, for wineries such as Acacia Winery, Chalone Wine Estates and Tolosa Winery on the Central Coast. He founded L.M. Brooks Consulting in 2000 after leaving executive winemaking, and continues to offer a wide range of services through this. Brooks has recently been lecturer in advanced sensory analysis of wine at both Cal Poly San Luis Obispo and at Fresno State University.

Morrison and Brooks discussed sensory trial best practices so that the results would provide value—not only for the various OTRs and their effects on Chardonnay, but also so that the winemakers in attendance could take back sensory trial methods back to their own wineries. Brooks also said that creating a panel of experienced tasters is one of the more difficult tasks in setting up a trial of this sort.

“It’s hard to put a good, trained, expert panel of tasters together. Winemakers come pre-trained, but also with pre-conceived notions and biases. The opportunity for a big group of winemakers to taste a well-setup experiment is great,” he said in a pre-session discussion.

At the start of the session, winemakers were given an online questionnaire that immediately sent answers/preferences electronically to a main hub. The tasters are then asked to rank their preferences of all three wines against the control—a paired comparison.

So, what were the results?

“What’s interesting to me is even though the control was obviously same for all tasters, one of the groups had a very different view of the control than the other group, which is something that happens a lot in sensory science. If you look at the two controls [displayed to attendees] on the far left, you wouldn’t think those are the same wine, yet they are,” said Brooks.

Tasters had no clear preferences among the various OTR liners, with nearly a third favoring each. 

This article originally appeared in the September 2017 issue of Wine Business Monthly