Understanding the Use of Wax Seals on Beer Bottles: A Brewer's Perspective

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In summary, a home brewer explains why some beer manufacturers hand dip the top of capped bottles in wax. This is to prevent oxygen from entering the bottle and oxidizing the beer, as even a small amount of oxygen can cause oxidation over time. The wax seal also makes it difficult for oxygen to diffuse through the membrane, preventing any potential leaks. Additionally, the high pressure of CO2 inside the bottle can push out any incoming gases, further preventing oxidation. However, the brewer notes that the process of putting on wax seals can be tedious and is typically only used for beers that are meant for aging. They also mention the importance of speaking in terms of partial pressures when discussing diffusion.
  • #1
x-ray vision
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On another message board I belong to, someone asked why some beer manufacturers hand dip the top of the capped bottle in wax. This is part of one reply given by a home brewer:
A brewer’s perspective:
A crown cap is not an absolute seal. Even though the headspace may be entirely CO2 (it rarely is), Oxygen still wants to be in there. It’s a simple law of partial pressures. With little to no O2 in there, there’s an inbalance, and the O2 will equalize eventually. Even if the brewer uses oxycaps, eventually the O2 absorbing properties will be used up, and you’ll be left with a beer that will oxidize. Besides, a brewer using oxycaps is practically admitting their bottling line is ****, and they need more help to get low airs in the headspace.

Now, putting a wax seal on prevents intake of oxygen, but in the case of beers not made for aging, it’s a pain in the ass. You need to get the beer cold, then trim the wax around the cap with a sharp knife in one smooth motion. I’ve only ever done 2 beers with this type of finish - a russian imperial stout, and a belgian dubbel. The stout is aging nicely, and the Dubbel, which was also bottle conditioned, showed no signs of oxidization(when tasted two years later).

Can this be correct? Since the pressure inside the bottle is higher than the pressure outside of the bottle, can oxygen from the air actually want to enter the bottle more than other gasses because "oxygen still wants to be in there"? Isn't it possible for a properly sealed capped bottle to never allow gasses to get in or out?
 
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  • #2
Just quite a stab in the preverbial dark but what about diffusion?

-NewScientist
 
  • #3
Yes, why not? CO2 is bigger then O2, so if there is no macroscopic flow, then O2 will diffuse through membrane faster then CO2. O2 has bigger velocity as well.
Anyway, if there is no macroscopic flow (i.e. gas is not pushing another gas out), the molecules will not "see" one another, so for oxygen the bottle will look like empty. Of cource, if there is a relatively big leak, then the outcoming CO2 flow will push all incoming gases away.
 
  • #4
I personally would think the bigger issue is keeping the CO2 *inside* the bottle. The partial CO2 pressure inside the bottle is much, much greater than the atmosphere...so that's a big issue.

As far as oxygen, here's my guess. I don't know the exact oxidation reaction(s) that so many beer snobs are deathly afraid of, but it's safe to assume that the O2 in bottled air is consumed. As the partial O2 pressure get's low enough, an equilibrium between the consumption of O2 by oxidation and the release of absorbed O2 will be reached.

Now, if you were to consume O2 by oxidation, then allow O2 from outside the bottle to creep in, the equilibrium will change allowing for further oxidation.

Side note-- make sure whenever you're talking about diffusion to speak in terms of partial pressures. The driving force for diffusion isn't total pressure, it's partial pressure (well, actually it's chemical potential (well, actually it's electrochemical potential...)).
 

1. Why do brewers use wax seals on beer bottles?

Brewers use wax seals on beer bottles for a variety of reasons. One of the main reasons is to provide a layer of protection for the beer inside the bottle. The wax acts as a barrier against oxygen and other contaminants, helping to preserve the flavor and quality of the beer. Additionally, wax seals can add a decorative and unique touch to the bottle, making it stand out on the shelf.

2. How is the wax seal applied to the bottle?

The process of applying a wax seal to a beer bottle is typically done by hand. The wax is melted down and then carefully poured over the top of the bottle, ensuring that it covers the entire cap and creates a seal around the edge. After the wax has cooled and hardened, it can be stamped with a design or logo to add a personal touch.

3. What type of wax is used for beer bottle seals?

There are a few different types of wax that brewers may use for their bottle seals. Some common options include natural beeswax, synthetic wax blends, and paraffin wax. The type of wax used may depend on the desired color, consistency, and level of protection needed for the specific beer.

4. Can wax seals affect the taste of the beer?

In most cases, wax seals should not have a significant impact on the taste of the beer. As long as the wax is applied properly and does not come into contact with the beer itself, it should not alter the flavor. However, if the wax is not applied correctly and begins to melt or break off, it could potentially affect the taste of the beer.

5. Are wax seals necessary for all types of beer?

No, wax seals are not necessary for all types of beer. They are more commonly used for specialty or limited edition beers, as well as higher-end or aged beers. These types of beers may benefit from the added protection and unique presentation that a wax seal provides. However, most standard beers do not require a wax seal.

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