Have you ever heard someone say, “Best case scenario: fill your wine tank with wine and eliminate headspace” as an answer to a question about how to best blanket wine with gas?
If so, you’re not alone.
When it comes to wine storage, headspace woes and the effects of dissolved oxygen (commonly abbreviated as DO) tend to dominate the conversation.
- What is the best gas to blanket my wine?
- How long should I leave the gas on above the wine’s surface?
- Doesn’t sparging eliminate the wine’s flavor?
- How do I sparge?
These are all valid questions, and short of quoting chemical gas laws, working with inert gas in the cellar can be confusing.
On January 22nd, DG Winemaking will host a FREE webinar featuring Luke Holcombe, Scott Labs Field Sales Representative, to talk about dissolved oxygen and its effects on wine stability.
In the cellar, practices using inert gasses usually circle around:
- Flushing tanks and hoses in between wine transfers
- Blanketing headspace (ullage)
- Sparging the wine
However, when it comes to working with inert gasses in the winery, there are a lot of practices, there are a lot of sayings, and, then, there are a lot of facts.
Don’t forget to flush your pumps and hoses
A previous article by D.L. Wilson (1985b) found that dissolved oxygen (DO) levels could be reduced with gas-flushing practices prior to a wine transfer. The DO pickup was further reduced when gas-flushing and sparging was used in combination.
To minimize DO pickup during a wine transfer, oxygen in the filling tank, the tank being emptied, and the hose lines with pump set up should all be considered. Flushing through hoses and pumps before wine is pumped through them is easily overlooked, but a relatively good practice for minimizing oxygen integration. Using “T” connections can introduce inert gas to the delivery line and help maintain a blanket of inert gas on the surface of the wine as it fills a new tank (D.L. Wilson, 1985b).
Why the flame test doesn’t work
Blanketing practices attempt to create a non-oxygen gas layer directly above the surface of the wine, or a blanket. Inert gas blankets are recommended as an alternative to filling tanks fully.
Darn it! Those previous wine experts you heard were right.
Filling tanks is usually best to minimize oxygen integration into the wine through storage while also reducing microbial risk. Coupled with temperature control and sulfur dioxide management, these three cellar practices can greatly reduce accelerated quality degradations of wine.
Inert gas blankets attempt to minimize (or eliminate) the oxygen layer above the surface of the wine. It’s assumed that by eliminating the oxygen, the wine cannot further oxidize, or support aerobic (oxygen-needing) microbial growth. In old winemaking practices, oil layers were used to separate the wine surface from the oxygen surface. However, this practice is not commercially recommended today.
Most experts agree that to avoid aerobic microbial growth, oxygen levels must be reduced to 0.5% or less (M. Dharmadhikari). [As a reference, air is made up of about 20.9% oxygen at 20°C at sea level (L. Nel, 1998).]
However many wineries do not measure the oxygen content in the headspace of the tank, let alone directly above the surface of the wine, to ensure the blanket is effective. D.L. Wilson (1985a) compared three carbon dioxide blanketing techniques with a 1 meter (3.28 feet) ullage space between the wine’s surface and the lid of the tank. The most effective treatment was using carbon dioxide gas directly at the wine’s surface to displace oxygen at the surface of the wine. In this case, oxygen was displaced up and out of the wine tank, showing additional decreases of the air’s oxygen content up to 50 cm away from the wine’s surface. This was compared to a dry ice treatment (that sublimates carbon dioxide) in a bucket or ice bucket with holes that hung from the top of the tank. With these later two treatments, approximately 13% – 19% of oxygen remained at the surface of the wine.
Without an oxygen meter, winemakers may rely on the “lit match” test because matches cannot sustain a flame in low oxygen environments. However, matches can extinguish at about 14% – 15% oxygen concentration, candles at 15%, and butane cigarette lighters at about 14.25% (G.K Smith, 1997). These limits are all well above the maximum 0.5% oxygen concentration required to inhibit microbial growth.
Do inert gasses gently push oxygen molecules out of the way?
In short, no.
While it may make for a nice image in our minds, the inert gasses we use in the cellar (nitrogen, carbon dioxide, and argon) are not that effective at sinking to the wine’s surface when blanketing. Several scientific papers have shown various blanketing inefficiencies in the cellar. Nitrogen, which is not heavier than oxygen, gently moves oxygen around and displaces oxygen. Based on how many wineries apply nitrogen gas, it can very quickly float above oxygen due to its lighter weight (L. Nel, 1998). However, there are ways to make nitrogen use more effective.
It is assumed carbon dioxide sinks below oxygen molecules, resting on the surface of the wine, due to its heavier molecular weight. However, as mentioned above, in practice, this is not the case. Instead carbon dioxide “uniformly distributes” (M. Dhardmadhikari) throughout the wine tank, diluting the oxygen concentration (L. Nel, 1998).
Carbon dioxide: not so inert
A further problem with carbon dioxide gas use is that it is soluble in wine. Argon and nitrogen are less soluble.
Gas laws permit the exchange of gas over the surface barrier. Therefore, it is possible that the wine absorb and retain dissolved carbon dioxide when it’s used as a blanketing gas.
Dissolved carbon dioxide actually has a sensory impact on the wine. The following are dissolved carbon dioxide levels and their associated sensory properties from D.L. Wilson (1985a):
- “<0.2 g/L: wine appears flat and unacceptable
- 0.4 – 0.5 g/L: wine fully develops
- >0.7 g/L: sharp prickling flavor develops, may be acceptable in some white wines
- >1.0 g/L: clear prickling sensation with some bubbles on the glass
- 1.7 g/L: wine is fully saturated at normal temperatures”
“Oh my goodness… what can I do about headspace, DO, and all the gas I’m buying?”
Do not fret!
There are always solutions to improve cellar operations. And luckily, I’m here to help you.
Most wineries can use inert gas to help them when headspace situations arise; they simply need to improve their cellar practices when applying inert gasses in production.
Because this is such a hot topic, you can join Luke Holcombe from Scott Labs on January 22nd for FREE through the DG Winemaking website. Luke’s presentation will cover:
- How DO contributes to stability and spoilage issues
- Easy-to-implement mitigation strategies (some of which will cover juicy concepts like sparging, which any-sized winery can do)
- Review bottle shock and barrel shock
All you have to do to attend this workshop is pre-register. No fees attached. Anyone is welcome to join. Once you register, a link will be emailed to the email address you used for registration. The link provides access to the webinar on January 22nd at 3:00 PM (EST)/2:00 PM (Central).
Dharmadhikari, M. Use of inert gasses. Available at: https://www.extension.iastate.edu/wine/use-inert-gases
Nel, L. (1998). The use of inert gas in the wine making process. Wynboer, Januarie. Pg. 101 – 103.
Smith, G.K. (1997). Presentation from the 21st Biennial Australian Speleological Federation Conference. Information provided by: Dr. Tom Cottrell, Extension Enologist of the University of Kentucky, 2013.
Wilson, D.L. (1985a). Storage of wine using inert gas for prevention of oxidation. Australian Grapegrower Winemaker, 256: 122-127.
Wilson, D.L. (1985b). Wine transfer using inert gas for prevention of oxidation. Australian Grapegrower Winemaker, 256: 110-111.