Degassing Wine: Removing Dissolved CO2 Before Bottling

Why Wine Needs Degassing

During fermentation, yeast produces carbon dioxide (CO2) as a byproduct of converting sugar into alcohol. In the vigorous bubbling phase of primary fermentation, most of this CO2 escapes through the airlock. However, a significant amount of CO2 remains dissolved in the wine itself, held in solution by the liquid's ability to absorb and retain gas.

This dissolved CO2 is not always obvious. The wine may look perfectly still in the carboy, with no visible bubbles, yet contain enough dissolved gas to produce an unpleasant fizz or spritz on the palate. If bottled in this state, the wine will have a slight carbonation that is considered a fault in still wines. The effervescence clashes with the smooth, flat texture expected of a properly finished still wine.

Additionally, dissolved CO2 interferes with several winemaking processes:

• Fining agents may not settle properly because rising micro-bubbles keep particles in suspension
• Sulfite additions are less effective because CO2 displaces SO2 in solution
• Clarity: Micro-bubbles can create a persistent, fine haze that mimics protein instability
• Flavor perception: CO2 amplifies the perception of acidity, making wine taste sharper and more aggressive than it actually is

Degassing is the process of removing this dissolved CO2 before bottling, ensuring a smooth, still wine with accurate flavor balance.

How Much CO2 Is Too Much?

A fully fermented wine at cellar temperature may contain 1,000-2,000 mg/L of dissolved CO2. For a perfectly still wine, the target is below 500-600 mg/L. Above this threshold, the CO2 is perceptible as a light prickle or spritz on the tongue.

For reference, sparkling wines like Champagne contain approximately 5,000-6,000 mg/L of dissolved CO2. So even a "gassy" still wine has far less carbonation than a sparkling wine, but enough to be noticeable and undesirable.

When to Degas

After Fermentation Is Complete

Do not attempt to degas wine that is still fermenting. Active yeast will continue producing CO2, immediately re-saturating the wine. Wait until fermentation is confirmed complete:

• Specific gravity is stable at 0.995 or below on two readings taken 48 hours apart
• No bubbles are passing through the airlock
• The wine has been racked at least once

Before Fining and Bottling

Degas the wine before adding fining agents and before bottling. As noted above, dissolved CO2 interferes with fining effectiveness and produces carbonation in bottled wine. The ideal sequence is:

1. Confirm fermentation complete
2. Degas
3. Add fining agents (if needed)
4. Cold stabilize (if needed)
5. Final sulfite adjustment
6. Bottle

Timing Considerations

Wines aged for 6 months or more in a carboy with an airlock will naturally off-gas most of their dissolved CO2 over time. Each racking also releases some CO2. If you are producing a wine with extended aging, aggressive degassing may not be necessary because the gas has had time to escape gradually.

However, wines made on a faster timeline, including many fruit wines, kit wines, and simple whites intended for early drinking, often reach the bottling stage with significant dissolved CO2 still present. These wines benefit most from active degassing.

Degassing Methods

Method 1: Agitation by Stirring (Manual)

The simplest method, requiring no special equipment.

Equipment needed: A sanitized stirring rod or long spoon

Procedure:

1. Remove the airlock from the carboy
2. Insert a sanitized stirring rod
3. Stir the wine vigorously for 3-5 minutes, creating a strong vortex
4. Rest for 5 minutes, then repeat
5. Continue for 3-5 cycles of vigorous stirring and resting
6. Replace the airlock

How it works: Stirring creates turbulence that brings dissolved CO2 to the surface where it escapes into the atmosphere. The vortex increases the surface area of gas-liquid contact, accelerating the release.

Effectiveness: Moderate. Manual stirring removes a significant portion of dissolved CO2 but may not achieve complete degassing in a single session. Repeat the process over 2-3 days if the wine still shows a spritz when tasted.

Method 2: Drill-Mounted Degassing Wand

The most popular method among home winemakers for its speed and effectiveness.

Equipment needed: A degassing wand (also called a wine whip or lees stirrer) attached to a standard cordless or corded drill. Cost: $10-20 for the wand.

Procedure:

1. Remove the airlock from the carboy
2. Insert the sanitized degassing wand through the carboy neck
3. Attach the wand to the drill
4. Run the drill at low speed for 30-60 seconds
5. Stop and allow foaming to subside (the CO2 release creates vigorous foaming)
6. Repeat for 3-5 cycles of 30-60 seconds each, with resting periods between
7. Total active stirring time: 3-5 minutes
8. Replace the airlock

How it works: The spinning wand creates powerful turbulence and a deep vortex that efficiently drives dissolved CO2 out of solution. This is dramatically faster and more effective than manual stirring.

Effectiveness: High. A drill-mounted wand is the single most effective degassing tool available to home winemakers. Most wines are fully degassed in a single session.

Caution: Use low speed only. High-speed agitation introduces excessive oxygen and can create foam that overflows the carboy. Also be careful not to hit the bottom or sides of a glass carboy with the wand, as this can crack the glass.

Method 3: Vacuum Degassing

Vacuum degassing uses negative pressure to pull dissolved CO2 out of solution.

Equipment needed: A vacuum pump (hand-operated or electric) attached to a carboy cap or stopper with a vacuum fitting. Some home brewing stores sell vacuum degassing kits for $20-40. A brake bleeder hand pump from an auto parts store is an inexpensive alternative.

Procedure:

1. Attach the vacuum fitting to the carboy
2. Pump to create a partial vacuum inside the carboy
3. Observe the wine: dissolved CO2 will come out of solution rapidly, creating vigorous bubbling and foaming
4. When the foaming subsides, release the vacuum
5. Repeat 3-5 times until pulling a vacuum produces no more visible gas release
6. Replace the airlock

How it works: Reducing the pressure above the wine lowers the gas's solubility, causing dissolved CO2 to rapidly escape from solution. This is the same principle as opening a bottle of soda: releasing the pressure allows the dissolved gas to escape as bubbles.

Effectiveness: Very high. Vacuum degassing is arguably the most thorough method because it directly addresses the physics of gas solubility.

Caution: Do not apply excessive vacuum to a glass carboy. The inward pressure differential can cause the carboy to implode. Limit vacuum to 10-15 inches of mercury and use short, repeated cycles rather than sustained vacuum.

Method 4: Warm Degassing

Warming the wine reduces CO2 solubility, encouraging gas release.

Equipment needed: None beyond a warm room or gentle heat source.

Procedure:

1. Move the carboy to a warm location (70-80F / 21-27C)
2. Allow the wine to warm for 24-48 hours
3. Stir gently once or twice during the warming period
4. Return to cellar temperature after degassing

How it works: Gas solubility in liquid decreases as temperature increases. Warmer wine holds less dissolved CO2, so the excess escapes naturally.

Effectiveness: Low to moderate when used alone. Best as a supplement to other methods. Warm the wine slightly before using a degassing wand or vacuum pump for maximum efficiency.

Caution: Extended warming of wine increases oxidation risk. Limit the warm period and ensure adequate sulfite protection.

Method 5: Time and Racking

The most passive method. Simply let time do the work.

Procedure: Age the wine in a carboy with an airlock for 3-6 months, racking every 6-8 weeks as needed.

How it works: Dissolved CO2 slowly diffuses out of the wine through the liquid surface and escapes through the airlock. Each racking exposes additional surface area and releases gas during the transfer.

Effectiveness: Complete, but very slow. Wines aged for 6+ months with multiple rackings are typically fully degassed. This is the default approach for wines on an extended aging timeline.

Testing for Dissolved CO2

The Shake Test

The simplest test for dissolved CO2:

1. Draw a small sample (50-100 ml) into a clean, clear bottle or jar
2. Cap the bottle tightly
3. Shake vigorously for 30 seconds
4. Immediately open the cap

If you hear a hiss of escaping gas, the wine still contains significant dissolved CO2 and needs further degassing. If opening the cap produces no sound and no visible gas release, the wine is adequately degassed.

The Taste Test

Pour a small sample and taste it. Dissolved CO2 produces a distinctive prickle or spritz on the tongue, particularly noticeable at the tip and sides. If you detect any fizzy sensation, the wine needs degassing.

The Visual Test

Pour a sample into a clear glass and hold it up to light. Look closely at the inside walls of the glass. If tiny bubbles cling to the glass and slowly rise, dissolved CO2 is present. A well-degassed wine shows no bubble formation on the glass walls.

Common Degassing Mistakes

Degassing Before Fermentation Is Complete

If fermentation is still active (even slowly), degassing is futile because the yeast will immediately produce more CO2. Always confirm fermentation is complete before degassing.

Not Degassing Enough

A single brief stirring session rarely achieves complete degassing. Most methods require multiple cycles of agitation and rest. Do not declare the wine degassed until the shake test confirms no gas release.

Using High-Speed Drill Settings

Running a degassing wand at high speed introduces far too much oxygen and can create uncontrollable foaming. Always use the lowest speed setting on your drill. The wand should spin fast enough to create a visible vortex but not so fast that wine splashes or the carboy rattles.

Degassing in a Sealed Vessel

Never attempt to degas wine in a fully sealed container. The released CO2 needs somewhere to go. If the vessel is sealed, pressure builds inside, and when you open it, the wine can foam out violently. Always degas with the vessel open or with a vacuum-rated fitting.

Skipping Degassing for Kit Wines

Wine kits are the most common offenders for residual CO2 because their accelerated timelines (4-8 weeks from start to bottle) do not allow enough time for natural off-gassing. If you make kit wines, always degas thoroughly before bottling.

Frequently Asked Questions

How do I know when wine is fully degassed?

Use the shake test: draw a small sample into a bottle, cap it, shake vigorously for 30 seconds, and open. If there is no hiss of gas and no visible bubbles on the inside of the glass when you pour a sample, the wine is fully degassed. Taste is also a reliable indicator; if there is no prickle or spritz on the tongue, the wine is ready.

Can I over-degas wine?

You cannot remove too much CO2 from a still wine. However, aggressive degassing methods that introduce excessive oxygen can harm the wine through oxidation. The risk is not from removing too much gas but from the oxygen pickup during the degassing process. Protect the wine with adequate sulfite and minimize the time the vessel is open.

How long does degassing take?

With a drill-mounted wand, most wines can be fully degassed in 5-15 minutes of active stirring spread over several cycles. Vacuum degassing takes 15-30 minutes. Manual stirring may require 2-3 sessions over several days. Passive degassing through time and racking takes 3-6 months.

Why does my wine still taste fizzy after degassing?

The most common reason is insufficient degassing. Repeat the process with more vigorous or prolonged agitation. Another possibility is that fermentation was not actually complete and the yeast is still producing CO2. Check the specific gravity to confirm fermentation is finished.

Should I degas wine before or after adding sulfite?

Degas before your final sulfite addition. Degassing introduces some oxygen, which consumes sulfite. By degassing first and then adding sulfite, you ensure the sulfite is working to protect the wine rather than being consumed by the oxygen introduced during degassing.