How does tonic water stay so fizzy?

[Chris Hennes]

It seems to me that tonic water, or at least the Schweppes I've got right now, retains its fizz better than pretty much any other carbonated beverage. I can leave the bottle open overnight, and when I go to dump it the next day it's still going strong. Capped and put back into the fridge it seems to retain full fizziness for days on end, unlike soda which invariably tastes flat after a day or two. What's going on here?

[Thanks for the Crepes]

Chris,

 

I have no idea, but I'd be very interested in any explanations, because my seltzer doesn't stay carbonated well overnight even tightly-capped with the bottle squished to get most air out and then placed in the fridge, especially if there's not much left in the two-liter plastic bottle.

 

I actually like tonic water, but avoid it because of the sweetener. I Googled, and apparently if you try hard enough unsweetened versions are available.

 

Do you mean that you left the uncapped bottle out on the counter overnight, and it still maintained carbonation, or am I misunderstanding?

[Simon Lewinson]

Chris,

 

I have no idea, but I'd be very interested in any explanations, because my seltzer doesn't stay carbonated well overnight even tightly-capped with the bottle squished to get most air out and then placed in the fridge, especially if there's not much left in the two-liter plastic bottle.

By squeezing out the air you will flatten the drink quicker. When you do this, you effectively reduce the pressure in the bottle and that draws dissolved gas out of he drink, flattening it more. Take it out of the fridge, pour what you need, cap tightly and put it back in the fridge immediately to minimize dissolved gas loss.

Simon

[Smithy]

Getting back to Chris' question, I suspect it has to do with the solubility of CO2 in tonic water as opposed to soda water or typical soft drinks.  What factors (other than temperature) would affect that?

[Chris Hennes]

Do you mean that you left the uncapped bottle out on the counter overnight, and it still maintained carbonation, or am I misunderstanding?

 

Exactly so: I'm always surprised to find that it's still fizzy, under conditions where a bottle of soda would be completely flat.

[dcarch]

Bubbles (fizz) in carbonated water are governed by the following:

 

1. temperature - the higher the temperature, the faster the CO2 escapes.

2. pressure - the higher the pressure the slower the CO2 escapes.

3. surface area - the larger the surface area, the faster the CO2 escapes.

4. agitation - the desolved CO2 in a solution is not stable, agitation will encourage CO2 to escape.

5. time -  the desolved CO2 in a solution is not stable, CO2 is constantly escaping, except in a pressurized enclosed container.

 

This is how I can have good enough fizzy tonic water, or other carbonated drinks all the time:

 

All carbonated waters are over carbonated in the beginning, and half way through a large bottle, the remaining half will get kind of flat.

 

So when a bottle is almost flat, I will open a new bottle and mix the flat tonic with some  new tonic. And when the new bottle is half empty and flat, it's time to open another new bottle for  mixing

 

dcarch 

[cdh]

It seems to me that tonic water, or at least the Schweppes I've got right now, retains its fizz better than pretty much any other carbonated beverage. I can leave the bottle open overnight, and when I go to dump it the next day it's still going strong. Capped and put back into the fridge it seems to retain full fizziness for days on end, unlike soda which invariably tastes flat after a day or two. What's going on here?

Hmmm... I've not noticed that behavior, but I'll trust your observant eye and believe that is the case.  Most reasonable explanation is that the bottlers put more gas into tonic than seltzer, etc, so it takes a longer time for it to leave.  There are probably quantitative tests that could be done to prove this hypothesis-- get accurate scale and weigh bottles of tonic and seltzer while fully carbonated, then unscrew the caps and see how many grams of gas left... or maybe pH... more CO2 in solution ==> more carbonic acid... but the tonic recipe already has citric in it, so I have no ideas how that would affect a comparative measurement and what it would tell you vis a vis seltzer... which should start somewhat below 7 due to carbonic and be a solid 7 when flat... 

[rotuts]

you would need a micro-micro-micro balance.  

 

but you've noted that by including 'accurate' in the definition of that scale.

[dcarch]

Hmmm..-----------------  There are probably quantitative tests that could be done to prove this hypothesis-- get accurate scale and weigh bottles of tonic and seltzer while fully carbonated, then unscrew the caps and see how many grams of gas left... or maybe pH... more CO2 in solution ==> more carbonic acid... but the tonic recipe already has citric in it, so I have no ideas how that would affect a comparative measurement and what it would tell you vis a vis seltzer... which should start somewhat below 7 due to carbonic and be a solid 7 when flat... 

 

Just tie a big balloon over the bottle, shake the bottle and check the volume of the balloon.

 

dcarch

[cdh]

All of this is a variation on the historical challenge problem "Weigh the smoke from my cigar"... whose solution is to weigh the cigar, incinerate it, and weigh the ash.  Subtract.

[cdh]

you would need a micro-micro-micro balance.  

 

but you've noted that by including 'accurate' in the definition of that scale.

Dunno about that.  The carbonator charges aim to add an 8g charge to a liter of water for middle of the road fizzyness. 8g is about 1/3 of an ounce, so not a vanishingly small amount.  My guess is that you might get 10-14g out of tonic. Easier to go by weight than by volume of balloon, I think.