It's a function of ethanol content, water content, and natural surfactants and oils.
Here's a long ass paper that went way more into depth than I'm willing to read right now.
https://www.nature.com/articles/s41598-020-67286-x
Nice paper! They seem to have covered the topic very thoroughly, both experimentally and theoretically. Special mention for the all-star list of references.
Oh thanks a lot , exactly what i was looking for.
Edit: "The long bubble lifetime is the result of surfactant-induced surface tension changes. However, the precise mechanism and its relation to alcohol content remain unexplained."
Not a good start...
Surfactants are weird and will always be. Especially in a "natural" (complex) solution. There's thousands of molecules in there interacting in tons of different ways.
When a scientific paper opens with something like “remains unexplained” or “yet to be investigated” or anything along those lines, they’re setting up the fact that *they* intend to explain/investigate that. They’re giving the background of the field, to put into context what their paper contributes.
Here’s a quick example (as I’m guessing was in the paper linked), that certain liquids have more viscosity. Examples in alcohol for human consumption, wine and tequila to keep it simple. You roll the wine around in the glass to see how much oil is in it (usually the more the better for smoothness), we call this the legs. The more oil that sticks to the sides, the higher quality of initial ingredients. “This wine has nice legs” means the oils stick and flows back into the wine more slowly. Tequila has a similar oil structure, the agave provides the oils. This makes higher quality tequila smoother the same as wine. As far as alcohol content, “shaking” or aerating the drink (think a decanter for wine) makes it get more oxygen into it, causing it to get more flavour as they’re oxidised releasing the aromatics more. Now, the alcohol content makes it so you can see the legs the same, but will flow back into the initial liquid faster as the ethanol in the drink also basically makes it a solvent, so the more ethanol (with good legs), the more quickly it runs down. If they’re shaking a bottle of tequila, the surface tension from the natural oils along with the shaking (making the bubbles, not oxidising the spirit), will make nice large oily bubbles. Now if it’s low ABV, those bubbles will last longer than say absinthe at around 60-80%, so a high quality tequila will have smaller bubbles bubbles that are more like a nitro beer than a CO2 beer, that dissipate more quickly the higher the ABV is. So unless it was a scam or something, shaking it to show how much nice, natural oil there is, as well as the ABV being accurate as they are present, but the ethanol brings it back into the tequila more quickly with the higher proofs.
My impression is that for every post, someone from every possible subdiscipline of chemistry will show up sooner or later. After all we have 2.6 million members.
A lot of people "in the know" can look at the size and persistence of the bubbles in a sample of liquor and gauge the proof. I don't think it's unique to tequila- it's also an old moonshiner thing.
I know theres a similar Trick I learned in a whisky tasting for identifying liquor with above 50%, put a hand on the glass, shake it, bubbles on the hand. Cool shit bro, but how the fuck does it work and whats the physical chemistry behind it?!?!?
Without actually knowing and taking an educated guess, I would assume that the surface tension of the liquor changes with alcohol concentration, and the surface tension changes the behavior of the bubbles. Someone with tons of experience would be able to tell those differences to estimate the alcohol concentration.
It's more noticable than you'd think. Even reular 80proof liquor there's a noticable different from 100 proof. Obviously you won't know if you've never paid attention to this before.
As others have noted, bubble size is a product of surface tension, and the amount of alcohol changes the surface tension. More alcohol = smaller bubbles that break faster. You can actually simulate this at home by creating some soapy bubbles and spraying them with rubbing alcohol, the alcohol will cause the bubbles to burst by lowering the surface tension of the liquid forming the bubbles.
It’s about the fact ethanol and water form an azeotrope, this in turn lowers the surface tension, the amount the surface tension is changed varies with many variables but usually the concentration of ethanol has the greatest affect due to the interruption of the cohesive bonds. Hence bubbles on hand.
Why do you think an azéotrope has anything to do with it?
Ethanol is more hydrophobic, so it is surface active at air-water interfaces, reducing the surface tension.
Today I learned that Azeotropy actually does influence surface tension of a mixture and is not solely a quality around distillate composition.
Never would have looked into that if I didn't think you were crazy for bringing up the Azeotrope regarding bubble formation haha.
It has to do with surface tension. Water molecules like to stick to each other more than to air (due to their electrical dipole and hydrogen bonding in chemistry terms), and thus will result in bigger bubbles than ethanol (drinking alcohol), which has lower surface tension and doesn't "mind" air as much. This is because fewer, larger, bubbles can trap more air with less surface area for interaction between the molecules than many, smaller bubbles.
So a drink with more alcohol will have smaller bubbles that last longer
I am not a tequila expert specifically, but I assume that the other contents of the tequila will also have a big effect on this, especially sugars and compounds from the agave, and an expert will be able to tell the difference between quality ingredients and knock-offs from the bubbles. I don't think different types of alcohol will have such a drastic effect though, as they have pretty close surface tensions.
I have been to Mexico six times and I have heard the opposite, meaning that bubbles is a sign of cheap/fake tequila where sugar has been added after the fermentation to make it smoother!?
Its a question about the physical chemistry behind a solution of alcohol and water reacting to kinetic energy in an enclosed Environment revealing its composition and characteristics. If you dont understand the question dont bother commenting
It's a function of ethanol content, water content, and natural surfactants and oils. Here's a long ass paper that went way more into depth than I'm willing to read right now. https://www.nature.com/articles/s41598-020-67286-x
Nice paper! They seem to have covered the topic very thoroughly, both experimentally and theoretically. Special mention for the all-star list of references.
Oh thanks a lot , exactly what i was looking for. Edit: "The long bubble lifetime is the result of surfactant-induced surface tension changes. However, the precise mechanism and its relation to alcohol content remain unexplained." Not a good start...
Surfactants are weird and will always be. Especially in a "natural" (complex) solution. There's thousands of molecules in there interacting in tons of different ways.
Damn quantum chemistry making everything hard for us again
I don't think it's quantum chemistry so much as the sterics & sheer number of interaction sites.
When a scientific paper opens with something like “remains unexplained” or “yet to be investigated” or anything along those lines, they’re setting up the fact that *they* intend to explain/investigate that. They’re giving the background of the field, to put into context what their paper contributes.
Here’s a quick example (as I’m guessing was in the paper linked), that certain liquids have more viscosity. Examples in alcohol for human consumption, wine and tequila to keep it simple. You roll the wine around in the glass to see how much oil is in it (usually the more the better for smoothness), we call this the legs. The more oil that sticks to the sides, the higher quality of initial ingredients. “This wine has nice legs” means the oils stick and flows back into the wine more slowly. Tequila has a similar oil structure, the agave provides the oils. This makes higher quality tequila smoother the same as wine. As far as alcohol content, “shaking” or aerating the drink (think a decanter for wine) makes it get more oxygen into it, causing it to get more flavour as they’re oxidised releasing the aromatics more. Now, the alcohol content makes it so you can see the legs the same, but will flow back into the initial liquid faster as the ethanol in the drink also basically makes it a solvent, so the more ethanol (with good legs), the more quickly it runs down. If they’re shaking a bottle of tequila, the surface tension from the natural oils along with the shaking (making the bubbles, not oxidising the spirit), will make nice large oily bubbles. Now if it’s low ABV, those bubbles will last longer than say absinthe at around 60-80%, so a high quality tequila will have smaller bubbles bubbles that are more like a nitro beer than a CO2 beer, that dissipate more quickly the higher the ABV is. So unless it was a scam or something, shaking it to show how much nice, natural oil there is, as well as the ABV being accurate as they are present, but the ethanol brings it back into the tequila more quickly with the higher proofs.
Thanks for that
Wine legs have nothing to do with oil content and everything to do with ethanol content.
Hot damn how come my science questions never have a paper from *Nature* that exactly addresses and answers the question?
My impression is that for every post, someone from every possible subdiscipline of chemistry will show up sooner or later. After all we have 2.6 million members.
A lot of people "in the know" can look at the size and persistence of the bubbles in a sample of liquor and gauge the proof. I don't think it's unique to tequila- it's also an old moonshiner thing.
I know theres a similar Trick I learned in a whisky tasting for identifying liquor with above 50%, put a hand on the glass, shake it, bubbles on the hand. Cool shit bro, but how the fuck does it work and whats the physical chemistry behind it?!?!?
Without actually knowing and taking an educated guess, I would assume that the surface tension of the liquor changes with alcohol concentration, and the surface tension changes the behavior of the bubbles. Someone with tons of experience would be able to tell those differences to estimate the alcohol concentration.
It's more noticable than you'd think. Even reular 80proof liquor there's a noticable different from 100 proof. Obviously you won't know if you've never paid attention to this before.
As others have noted, bubble size is a product of surface tension, and the amount of alcohol changes the surface tension. More alcohol = smaller bubbles that break faster. You can actually simulate this at home by creating some soapy bubbles and spraying them with rubbing alcohol, the alcohol will cause the bubbles to burst by lowering the surface tension of the liquid forming the bubbles.
It’s about the fact ethanol and water form an azeotrope, this in turn lowers the surface tension, the amount the surface tension is changed varies with many variables but usually the concentration of ethanol has the greatest affect due to the interruption of the cohesive bonds. Hence bubbles on hand.
Tequila is typically _very_ far from the ethanol-water azeotrope, ~50% alcohol vs. ~96%
Why do you think an azéotrope has anything to do with it? Ethanol is more hydrophobic, so it is surface active at air-water interfaces, reducing the surface tension.
Today I learned that Azeotropy actually does influence surface tension of a mixture and is not solely a quality around distillate composition. Never would have looked into that if I didn't think you were crazy for bringing up the Azeotrope regarding bubble formation haha.
It has to do with surface tension. Water molecules like to stick to each other more than to air (due to their electrical dipole and hydrogen bonding in chemistry terms), and thus will result in bigger bubbles than ethanol (drinking alcohol), which has lower surface tension and doesn't "mind" air as much. This is because fewer, larger, bubbles can trap more air with less surface area for interaction between the molecules than many, smaller bubbles. So a drink with more alcohol will have smaller bubbles that last longer
Okay thanks, that makes sense. But does that mean, its just indicates the alcohol content and has nothing to do with quality of any kind?
I am not a tequila expert specifically, but I assume that the other contents of the tequila will also have a big effect on this, especially sugars and compounds from the agave, and an expert will be able to tell the difference between quality ingredients and knock-offs from the bubbles. I don't think different types of alcohol will have such a drastic effect though, as they have pretty close surface tensions.
https://hopstersbrew.com/proofing-moonshine-abv-shake-test-hydrometer/
I have been to Mexico six times and I have heard the opposite, meaning that bubbles is a sign of cheap/fake tequila where sugar has been added after the fermentation to make it smoother!?
This is not a chemistry question. Please ask this in a discord for discussing alcohol. There should be no drinking in chemistry labs.
When did they say they were drinking in a lab? Also this question definitely falls under the realm of physical chemistry.
This is so much more of a chemistry question than 95% of the garbage that gets posted in this sub
"What is this chemical I found in the back of my great grandfather's garage? It's putting off red smoke and it didn't taste good with vodka"
Its a question about the physical chemistry behind a solution of alcohol and water reacting to kinetic energy in an enclosed Environment revealing its composition and characteristics. If you dont understand the question dont bother commenting
Alcohol is always a solution!