Oxygen in Wine: What Ullage Means for Your Cellar

Understanding oxygen in wine, particularly through ullage, provides critical insight into a bottle's past and future. Ullage is the headspace of air between the wine and the top of its container. It serves as a key indicator for collectors assessing potential quality and value. That matters especially for older vintages, according to WineBid. Some oxygen is beneficial for wine maturation. Excessive exposure can lead to oxidation and various wine faults. Auction houses and after-market resellers closely inspect ullage levels. They use them to determine a wine's condition and resale value. That makes ullage a vital factor in deciding whether to hold, open, or sell a bottle from your cellar.

What is ullage and why does it matter for your collection?

Ullage is also known as the fill level or headspace. It is the gap between the cork in the bottle and the wine itself, as Decanter describes it. This space is primarily a mixture of alcohol and water vapors with carbon dioxide. In containers that are not completely airtight, such as cork-stoppered wine bottles, oxygen can also seep into this space. Producers typically aim for initial fill levels of 3-10mm at the time of bottling. That figure comes from Dirceu Vianna Junior MW, cited by Decanter. Over time, wine is lost through cork absorption and evaporation. The ullage increases.

The ullage level is a significant indicator. It reflects the care and storage conditions a wine has experienced. Matt Walls, DWWA regional chair for Rhône, told Decanter.com in 2018 that it is "the best guide you have to the condition of a bottle of wine, especially if you don't know for certain how it's been stored." A greater amount of ullage generally suggests a higher potential for the wine to have been exposed to harmful levels of oxidation. That affects its resale value. David Dudley-Jones of Dudley Jones Fine Wines stated in Decanter magazine in 2016 that "lower fill levels [in the bottle neck] and resultant seepage usually point to heat exposure and poor storage." Julia Sewell, sommelier at The Fat Duck, adds that "age aside, ullage lower than midshoulder level poses a much higher risk of spoilage," as reported by Decanter.

How does oxygen enter a bottled wine?

Oxygen enters bottled wine primarily through the cork stopper. It also enters, significantly, at the interface between the cork and the glass bottleneck. A study by Chanut et al. (2023) examined microagglomerated cork stoppers in model wine. The oxygen diffusion coefficient of the cork stopper alone remained unchanged over 24 months, regardless of storage conditions. However, the presence of model wine at 20°C significantly increased total oxygen transfer. The glass-cork interface accounted for nearly 75% of this transfer compared to cork studied without model wine, according to Chanut et al. (2023). This suggests that the interaction between the wine and the stopper's surface plays a crucial role. The paraffin and silicone coating matters in particular.

The natural process of evaporation and diffusion also contributes to oxygen ingress. As wine ages in the bottle, some wine is lost through the permeable cork. That causes the ullage to increase. If a wine is stored on its side, in contact with the cork, some wine is also lost by absorption into the cork. Longer corks potentially absorb more wine and thus create more ullage. WineBid terms this continuous, slow escape of wine seepage. It can be due to the natural cork lifecycle or storage conditions.

What are the signs of excessive oxygen exposure?

Excessive oxygen exposure can lead to various wine faults. Those faults significantly diminish a wine's quality. The Australian Wine Research Institute (AWRI) identifies several oxidation-type faults. Oxidation, particularly in white wines, can manifest as a "dulling of the aroma," progressing to "cardboard," "straw," and "hay-like" aromas, and in extreme cases, "sherry-like," "madeirised," "wet wool," "wet dog," or "varnish-like" characteristics. Red wines have a higher content of phenolic compounds acting as natural antioxidants. They can withstand more oxidation during handling.

Acetaldehyde increases as wines age due to the chemical oxidation of ethanol, the AWRI reports. It can impart odours described as "over-ripe bruised apples," "stuck ferment" character, or "sherry" and "nut-like" characters. Ullaged tanks, for example, can lead to surface yeast infection where acetaldehyde is produced. Volatile acidity (VA), often perceived as the odour of "vinegar," is primarily due to acetic acid. Acetic acid bacteria convert it from alcohol in the presence of oxygen, according to the AWRI. A sound wine typically has VA in the range of 0.1-0.4 g/L immediately after fermentation. Concentrations above 0.7 g/L are generally considered detrimental. Ethyl acetate, with a "nail polish remover" odour, can contribute "fruity" aroma properties at low levels (30-60 mg/L). It becomes a defect at higher concentrations (150-200 mg/L), the AWRI states. Finally, "mousiness," an off-flavour reminiscent of "caged mice" or "cracker biscuit," is often perceived late on the palate. Exposure to air or oxygen can enhance it, particularly in wines with low sulfur dioxide and low acidity, the AWRI notes.

How do ullage levels guide your decisions?

Ullage levels provide a crucial guide for collectors deciding when to open or continue holding a bottle. That is particularly true for older wines. Standard descriptions for fill levels vary between Bordeaux and Burgundy wines. Their bottle shapes differ, as WineBid note.

Michael Broadbent developed his guide in the late 1980s, and the wine market uses it widely. It primarily focuses on Bordeaux bottles. WineBid provides similar guidance, defining "base of neck or higher"a perfect fill level for any bottle of any age. Very"very top shoulder"excellent for wines more than 35 years old. Five"top shoulder" fill is acceptable and normal for wines 15 years of age and older, and "very good"for wines 35 years of age and older. Mid"mid shoulder"may be normal for a wine that is 40 years old or older. Low"low shoulder" occurs in older wines, WineBid states. Decanter also cites Christie's guidance from 2013, which describes "top shoulder"normal for any claret 15 years or older, while"mid-shoulder"abnormal for a 30 to 40-year-old wine, says Christie's"low shoulder" fill for Bordeaux is considered "and usually only accepted for sale if wine or label exceptionally rare or interesting'," according to Christie's guidance cited by Decanter.

For Burgundy, Pinot Noir, and similar bottles, ullage is measured in centimeters from the cork. WineBid considers "two centimeters or less" an excellent fill for any age. "Three centimeters" is perfectly normal for wines 12 years and older. It is excellent for wines 25 years or older. "Four centimeters"for wines more than 20 years old and excellent for wines more than 35 years old."Five centimeters" is not uncommon in wines 30 years old or older. Christie's, as reported by Decanter, adds that "condition and drinkability of Burgundy is less affected by ullage than its equivalent from Bordeaux," and gives a figure. Ullage of up to 7cm is relatively normal in 30-year-old Burgundy.

Here's a comparison of common ullage terms:

Ullage Level (Bordeaux/Cabernet Sauvignon)	Age Assessment
Base of neck or higher	A perfect fill level for any bottle of any age, WineBid states.
Very top shoulder	An excellent fill level for any wine more than 20 years old, according to WineBid.
Top shoulder	Acceptable and normal for wines 15 years of age and older, and very good for wines 35 years of age and older, WineBid states. Christie's, cited by Decanter, calls it normal for any claret 15 years or older.
Mid shoulder	May be normal for a wine that is 40 years old or older, WineBid states. Christie's, cited by Decanter, does not consider it abnormal for a 30 to 40-year-old wine.
Low shoulder	Occurs in older wines, according to WineBid.

A low fill can indicate seepage and oxidation, and it can affect a bottle's value considerably, WineBid notes. Our guide to ullage levels sets out every band and what each auction house publishes against it.