What’s the Difference Between Lathering Shaving Soap and Aerating Wine?
When We Create Lather or Swirl a Glass of Wine, We’re Actually Doing Two Very Different Things
While lathering shaving soap one day, I suddenly had a thought.
Swirling a glass of wine before drinking it and working a shaving soap with a brush both involve mixing air into something, don’t they?
But from a chemist’s point of view, these are two completely different phenomena.
Lathering Is a Physical Phenomenon; Oxidation Is a Chemical Change
Soap is made up of fatty acid salts. Its molecules have two distinct parts: a water-loving head and an oil-loving tail.
When you vigorously work the soap with a brush, air is forced into the water, creating countless gas–liquid interfaces.
The soap molecules move toward these interfaces and align themselves along them.
The hydrophobic tails orient toward the air, while the hydrophilic heads face the water.
This arrangement lowers surface tension and stabilizes the thin films surrounding the bubbles.
Throughout this process, the molecules themselves do not change. They are simply being rearranged.
That is why, even after the lather collapses, you can work the soap again and create lather once more.
Wine aeration is different.
When you swirl wine or decant it, the surface area in contact with air increases.
Dissolved oxygen can then actually oxidize polyphenols such as tannins and anthocyanins.
The oxidized compounds can polymerize, which softens the wine’s astringency.
Sulfur compounds produced during fermentation may also be oxidized or become volatile and dissipate.
These are reactions that change the molecular structure of the compounds themselves, making the process fundamentally different from lathering.
So, in simple terms:
Lathering is a physical process that changes form, while aeration is a chemical process that can change properties.
The only thing they have in common is that air acts as the medium. Their underlying mechanisms are completely different.
But Oxidation Can Occur in Soap, Too
There is one more point worth considering.
If the saponification reaction is not completed, unreacted sodium hydroxide (or potassium hydroxide) may remain in the soap.
This alkali first absorbs moisture from the air. On the soap’s surface, it can then react with carbon dioxide and gradually be converted into carbonate.
This is often what people refer to as “curing” or “aging” the soap. It is neither fermentation nor additional saponification.
The problem is that while this reaction can occur on the surface of the soap, it may not proceed evenly throughout the interior.
Even after a soap has been left to age for a long time, the surface may have undergone carbonation while unreacted alkali remains inside. This residual alkali can become a source of skin irritation.
Meanwhile, fatty acids containing double bonds, such as oleic acid and linoleic acid, can undergo oxidation through a separate pathway.
Light, heat, and trace metal ions can trigger radical chain reactions, eventually producing aldehydes and ketones. These compounds are responsible for the characteristic rancid odor that can develop in soap.
This reaction is not directly related to alkali. However, an incompletely saponified batch tends to contain more unreacted oils, and those oils are more susceptible to oxidation.
In the End, We Come Back to the Same Question
Once again, we can see why it is important to carry the saponification reaction through to completion.
Creating a good lather and making a soap that is gentle on the skin may seem like two separate issues.
But when you follow the chemistry all the way down to its roots, they eventually lead to the same question:
How completely did the reaction proceed?
Dr. Dongju Jeon, Director of R&D at Hwayeon Soap (hwayeon.co.kr) and Terry's Soap
What’s the Difference Between Lathering Shaving Soap and Aerating Wine?
When We Create Lather or Swirl a Glass of Wine, We’re Actually Doing Two Very Different Things
While lathering shaving soap one day, I suddenly had a thought.
Swirling a glass of wine before drinking it and working a shaving soap with a brush both involve mixing air into something, don’t they?
But from a chemist’s point of view, these are two completely different phenomena.
Lathering Is a Physical Phenomenon; Oxidation Is a Chemical Change
Soap is made up of fatty acid salts. Its molecules have two distinct parts: a water-loving head and an oil-loving tail.
When you vigorously work the soap with a brush, air is forced into the water, creating countless gas–liquid interfaces.
The soap molecules move toward these interfaces and align themselves along them.
The hydrophobic tails orient toward the air, while the hydrophilic heads face the water.
This arrangement lowers surface tension and stabilizes the thin films surrounding the bubbles.
Throughout this process, the molecules themselves do not change. They are simply being rearranged.
That is why, even after the lather collapses, you can work the soap again and create lather once more.
Wine aeration is different.
When you swirl wine or decant it, the surface area in contact with air increases.
Dissolved oxygen can then actually oxidize polyphenols such as tannins and anthocyanins.
The oxidized compounds can polymerize, which softens the wine’s astringency.
Sulfur compounds produced during fermentation may also be oxidized or become volatile and dissipate.
These are reactions that change the molecular structure of the compounds themselves, making the process fundamentally different from lathering.
So, in simple terms:
Lathering is a physical process that changes form, while aeration is a chemical process that can change properties.
The only thing they have in common is that air acts as the medium. Their underlying mechanisms are completely different.
But Oxidation Can Occur in Soap, Too
There is one more point worth considering.
If the saponification reaction is not completed, unreacted sodium hydroxide (or potassium hydroxide) may remain in the soap.
This alkali first absorbs moisture from the air. On the soap’s surface, it can then react with carbon dioxide and gradually be converted into carbonate.
This is often what people refer to as “curing” or “aging” the soap. It is neither fermentation nor additional saponification.
The problem is that while this reaction can occur on the surface of the soap, it may not proceed evenly throughout the interior.
Even after a soap has been left to age for a long time, the surface may have undergone carbonation while unreacted alkali remains inside. This residual alkali can become a source of skin irritation.
Meanwhile, fatty acids containing double bonds, such as oleic acid and linoleic acid, can undergo oxidation through a separate pathway.
Light, heat, and trace metal ions can trigger radical chain reactions, eventually producing aldehydes and ketones. These compounds are responsible for the characteristic rancid odor that can develop in soap.
This reaction is not directly related to alkali. However, an incompletely saponified batch tends to contain more unreacted oils, and those oils are more susceptible to oxidation.
In the End, We Come Back to the Same Question
Once again, we can see why it is important to carry the saponification reaction through to completion.
Creating a good lather and making a soap that is gentle on the skin may seem like two separate issues.
But when you follow the chemistry all the way down to its roots, they eventually lead to the same question:
How completely did the reaction proceed?
Dr. Dongju Jeon, Director of R&D at Hwayeon Soap (hwayeon.co.kr) and Terry's Soap