Feature Article from the September 2009 Magazine Issue
Indispensable Inert Gas
Producing better white wine using CO2, nitrogen and argon
by Chris Stamp
WINE EAST HIGHLIGHTS
- Managing oxygen exposure is one of the most important jobs a winemaker can do.
- Rinsing the tank with hot water before closing it up, then gassing it with CO2, can create a protective blanket.
- Every month or so, top off tanks with inert gas.
As earthlings, we live at the bottom of a giant ocean of air. Roughly 21% of this gaseous ocean is made up of oxygen, which is essential for life. Although we cannot survive without it, ironically it is what ages and eventually wears out our mortal coils. This irony is also true of wine. Wine requires oxygen, yet oxygen inevitably leads to its demise.
One of the most significant functions winemakers perform is managing the availability of oxygen to wine. It's easy to imagine how, at the bottom of this ocean of air, oxygen leaks into everything. Even with stainless steel tanks, solid silicone bungs and sealed manways, oxygen finds its way in. Therefore, winemakers expend significant energy protecting their wine from oxygen. If a winemaker fails in this regard, his wines will essentially die an early death--sometimes before they even get into the bottle.
Excessive oxygen exposure manifests itself first by reducing fruity aromas. From there, the negative effects of oxygen exposure in the wine are demonstrated by nutty aromas and an unattractive color. Oxygen also provides growth potential for a host of spoilage microorganisms, such as film yeast and acetobacter, producing negative aromas and flavors.
Wines vary in their capacity to take on oxygen before crossing the line from well developed to oxidized. Reds, which are higher in oxygen-absorbing phenolics, can handle a higher level of oxygen exposure. Winemakers from regions known for big, high-tannin reds may practice relatively oxidative winemaking. This approach helps soften and evolve overly tannic wines.
These same practices applied to whites would be disastrous. Wines, especially fruit-driven whites, are best handled in a reductive fashion. Generally there is plenty of incidental oxygen uptake through the course of normal winemaking to allow these wines to develop.
Inert but indispensable
Inert gases--namely carbon dioxide, nitrogen and argon--are indispensable in reductive winemaking. Inert gases are used to supplant air in places where air could come into contact with wine. Unfortunately, inert gases are underutilized by many winemakers.
It is a good practice to gas tanks prior to filling them with wine. The most efficient way to gas a tank is through the bottom valve. A good setup for this task is a length of three-eighths to one-half-inch plastic tubing with the appropriate fitting for your gas cylinder attached to one end. There is really no need for a regulator for this function. On the other end of the plastic tubing, attach a nipple tapped into a drilled end cap that fits your tank valve. This fitting can be easily clamped to the bottom valve of your tank.
While purging the entire tank with inert gas prior to filling would be great, it is usually not practical due to the time involved and the amount of gas it would require. A good compromise is to put a blanket of CO2 in the bottom of the tank. Fill the tank with wine (slowly at first, to avoid splashing). Once your wine transfer is complete, purge the headspace with the inert gas of your choice.
One trick that can help achieve a good gas blanket is to rinse the tank with hot water before closing it up. This serves to warm up the air inside the tank, making it lighter. Then, while the tank is still warm, gas it with CO2, which is a good candidate for this purpose for several reasons. Not only is CO2 the cheapest of the three gases mentioned, it is also heavier than nitrogen. And, since carbon dioxide cylinders are filled with liquid CO2, there is a phase change as you draw gas from the cylinder. This phase change from liquid to gas cools the CO2, making it much denser, so it sits better on the bottom of the tank.
You can actually check your gas blanket by opening the bottom valve after gassing and sniffing for CO2. There are no special instruments required. A simple sniff is usually enough to tell if your tank has been adequately purged. If your head snaps back from the sting of carbonic acid forming in your nasal passages, you're done. This is another advantage of using CO2: its ease of detection. Nitrogen, on the other hand, is odorless and tasteless and provides no such sensation, except that you suddenly feel out of breath and dizzy. This happens just before you fall off the ladder.
When you're done filling the tank with wine, hook the gas up again and bubble it through the wine to purge out the headspace. If you are using CO2, a simple sniff test at the top port is all you need to confirm complete evacuation of air.
Argon and nitrogen are a little trickier. You can use an oxygen meter if you have one. Use a target oxygen level of less than 0.5%. If you lack fancy equipment, a lighted match will do. With the gas off, slowly insert a lit match into the top port. The flame, including its ember, should instantly extinguish upon entering the port if the headspace has been adequately sparged. Tanks should be "topped up" with inert gas every month or so--and more often if the wine is in a plastic tank, if there is considerable headspace or if there are big temperature fluctuations in the cellar.
Some other notes on inert gases: Argon is the most expensive, but some winemakers prefer it because it's the densest of the three gases. Being a heavier gas it may have better blanketing properties, but atomic mass will only go so far. There are many other forces at work that cause convection in a tank. The concept of blanketing a wine for more than just short-term protection won't work. Thorough purging of the headspace is a much more reliable approach.
One drawback to CO2 is its solubility in wine. If used right up until bottling, especially if the wine is cold, it may result in an unacceptable level of carbonation. To avoid this, switch to nitrogen a month or two before bottling.
Not just for tanks
The use of inert gases shouldn't be limited to tanks. Hoses and filters can all be easily flushed with the same setup described above. This is especially important when working with cold wine. While oxidative reactions don't occur as quickly in cold wine as compared to warmer wine, oxygen dissolves much more readily and will eventually degrade wine quality. Sparging glass before filling can greatly reduce oxygen pickup during bottling.
Just after alcoholic fermentation, young wine may seem somewhat immune to oxidation, partly because of dissolved CO2 and partly because of its reductive state resulting from the action of yeast scavenging for oxygen during its growth phase. This is no reason to be complacent. While dissolved CO2 helps provide a bit of a protective blanket for the wine, careless handling will still dissolve oxygen. High levels of dissolved CO2 do not preclude oxidation.
Despite our best efforts, even good winemakers can make mistakes and occasionally end up with a wine that is pushing the envelope of its oxygen capacity. While there is no perfect cure, many wines can be dramatically revived. Mildly oxidized wines (especially if they are still young) can sometimes be rejuvenated with a casein fining.
Another approach to resuscitating oxidized wine is to add it to an actively fermenting must, but this has its own set of perils, such as stressed yeast aromas and stuck fermentations, and should be monitored carefully. Oxidized wine might be diverted to other products like sherry, port or vinegar. Just remember, the worst thing you can do with oxidized wine is to bottle it.
When it comes to wine and oxygen, it's better to err on the side of caution. With the exception of wines with reduced sulfur compounds, less is usually better. By following good cellar practices, utilizing inert gases and adequate SO2 levels, a winemaker can dependably prevent what is probably the most common wine flaw, oxidation, and keep his or her wines youthful and vibrant. If only it were this easy for us earthlings!
Chris Stamp is president and winemaker at Lakewood Vineyards in Watkins Glen, N.Y. He started his career in wine as winemaker at Plane's Cayuga Vineyards in the Finger Lakes, and in 1986 took a position as enology research and extension associate at the Ohio Agricultural Research Development Center in Wooster, Ohio. When his family opened Lakewood Vineyards winery in 1988, he returned to New York to become the winemaker there. To comment on this article, e-mail edit@winesandvines.com.
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