What is it about wax on a wine bottle that makes me want to buy it? I really like it. Faced with a row of bottles that I don’t know, with no information other than the label, I’m drawn towards bottles sealed with wax. It looks premium. And because it is normally done manually (there are some automated waxing devices, but they aren’t common), it shows that some care has been taken. Also: this is likely to be smaller-production wine, and in the world of wine, smaller is often more beautiful (but not always).
So is wax just pretty, or does it serve a functional role? What does the science say?
The term used here is overcapping, and it’s important to differentiate between this, where wax is used over the top of the bottle neck and the in neck closure, and the wax treatments used on the surface of the cork.
Most of the oxygen transmission with a cork doesn’t come from oxygen moving through the body of the cork, but through the cork/glass interface. This can be shown by using epoxy resin to seal around the top of the cork where it meets the glass (epoxy doesn’t allow oxygen transmission), leaving the rest of the surface of the cork without any covering. This effectively eliminates oxygen transmission.
There have recently been some interesting studies addressing the potential oxygen barrier benefits of overcapping with wax from the group of Thomas Karbowiak at the University of Bourgogne.
“Nonetheless, there are still some winemakers maintaining the tradition of using wax, often in combination with cork-based stoppers, to enhance the overall aesthetics and brand image of a wine. Moreover, there is still a widespread belief that the addition of wax on top of the cork stopper helps to strengthen the seal and adds an additional layer of protection against oxidation of the wine, especially in the case of wines destined to age. This is somehow contradictory with the fact that the most commonly used waxes for sealing wine bottles are selected without taking into consideration their performance as barriers to oxygen. This is a very important parameter since the oxygen performance can vary depending on the type of wax used and its chemical composition.”
Ureña et al 2024
First, they too four different wax coatings and studied the oxygen barrier properties of these coatings alone. Beeswax, shellac and microcrystalline wax all performed similarly, with an oxygen transmission rate of around 8 mg oxygen per year for a cylindrical surface of 18.5 mm, equivalent to the surface of the cork inside a bottle neck. A commercial wax blend that they used performed a lot better, with an OTR some 10 times lower. This is the one they used in the study. They didn’t specify the manufacturer, but state that this is a blend of resins, refined hydrocarbon waxes and polymers.
Then they took natural cork and an agglomerated technical cork, and studied how they performed over a year in a number of settings, with and without wax. The corks were 25 mm x 49 mm, while the microagglomerated corks were 25 mm x 44 mm. They looked over one year storage using 375 ml bottles that had a PreSens chemoluminescent oxygen detector glued into the inside wall.
The first thing to note is that when a closure is inserted into a bottle neck, it is compressed. For most corks, the diameter of the uninserted cork is 25 mm, and this is then compressed to the 18.5 mm diameter of the bottle neck. This compression results in the release of gas (air) in the cork structure, and this outgassing takes 6 months in this study. It’s only after 6 months that you reach a sort of steady-state oxygen transmission level, and this is the bit where we really want to see the impact of any wax overcapping.
The second thing to note is that if the cork isn’t coated with wax before insertion, the oxygen transmission rate is very high. A wax coating (which all corks have, because it reduces the extraction force to a sensible level) eliminates a lot of the cork/glass interface oxygen transmission. This study looked at both treated and untreated corks and microagglomerate corks.
The third thing to note is that if you apply wax immediately after the cork is inserted, the outgassing disrupts the wax seal. But in the experiment where they looked at untreated corks, they had to apply the wax straight after corking because otherwise the glass/cork interface OTR would mask any findings, because it is so high.
So, the findings. The microagglomerates had a low OTR and the wax made no difference to the results.
The corks had a wide variation in OTR, ranging from 0.3 to 56.5 mg of oxygen, a 200-fold difference. But the high level was an outlier of the 9 bottle sample, and you would need a much larger sample size to make firm conclusions because of the natural variability of the cork. But with wax, the rate ranged from 0.3 to 3 mg. This seems to show that it’s having some effect reducing the variability, although with a sample of just 9 bottles we don’t know for sure that any of this set of 9 would have shown higher OTR without the wax.
The conclusion here is that if the closure has a lower permeability than the wax, and has a surface treatment (which all corks do), then the wax is providing a purely cosmetic role.
If the closure has a higher permeability than the wax, then wax may be providing some protection, and lowering the variability found with natural cork.
In a second study, the same group looked at the temperature of the bottleneck during wax application, and found that if the bottle neck was heated to 60-70 °C before waxing, then there was much stronger adhesion leading to higher barrier properties of the wax. If the wax is applied to glass at 25-50 °C, then the oxygen transmission rate is highly variable.
It follows that if you are worried about the variation in cork performance and you want wax to even this variation out, then heat the glass before applying the wax.
References:
María Ureña, Julie Chanut, Vincent Bottreau, Jean-Pierre Bellat, Régis D. Gougeon, Aurélie Lagorce, Thomas Karbowiak 2024 Wine bottle overcapping wax: An aesthetic or functional element? Food Packaging and Shelf Life 46:101367
Julie Chanut, María Ureña, Vincent Bottreau, Agathe Pissis, Jean-Pierre Bellat, Régis D. Gougeon, Aurélie Lagorce, Thomas Karbowiak 2026 Impact of the deposition process on oxygen barrier properties of wine bottle overcapping waxes. Food Packaging and Shelf Life 57:101814
Julie Chanut, Maria Ureña, Vincent Bottreau, Régis D. Gougeon, Jean-Pierre Bellat, Aurélie Lagorce, Thomas Karbowiak 2026 Wine bottle overcapping wax: is it an effective barrier to oxygen or just an aesthetic element? IVES Conference Series, WAC–IVAS 2026
I’m apparently just as susceptible to the wax = someone cared about this bottle heuristic. There’s something amusing about learning that one of the details I instinctively read as a signal of seriousness may, with the right closure, be doing essentially nothing beyond looking serious.
These are greaties, thanks for sharing.