[Paul]

Paul asked the Naked Scientists:
Hi Everyone, Love your show and thanks for answering my questions in the past.

Question: Why do we use carbon dioxide in the fizzy drinks? Could it be another gas, say nitrogen?

Many thanks, Paul
What do you think?

[chris]

Hi Paul

a good question. The reason is that carbon dioxide is relatively soluble in water, compared with nitrogen which dissolves only poorly. Also, when CO2 dissolves, it reacts with water molecules to produce carbonic acid which dissociates into hydrogen ions (acid) and bicarbonate ions:

CO2 + H2O -> H2CO3 -> H+ + HCO3-

Apart from being the mechanism by which limestone caves are formed, the H+ ions also impart a subtle lemony flavour to the liquid, adding to the overall taste sensation of the drink.

The CO2 bubbles therefore achieve several things:

1) They dissolve easily, enabling the drink to be made nice and fizzy and remain so for a reasonable time.

2) They bubbles come out of solution readily when given a suitable surface for nucleation, contributing to the texture of the drink.

3) The acid produced by the reaction of the CO2 with water adds to the flavour and taste sensation.

Hope that helps

Chris

[Kryptid]

I think it may have something to do with the solubility of carbon dioxide when compared to nitrogen. At 20 degrees Celsius, Carbon dioxide's solubility in water is 1.688 grams per liter, whereas nitrogen's solubility is 0.019 grams per liter. That means you can put a lot more carbon dioxide in water than nitrogen. Why is this?

In chemistry it is known that nonpolar molecules tend to dissolve best in nonpolar solvents. Polar molecules and ions tend to dissolve best in polar solvents. A polar molecule is a molecule that has a slight distribution of electric charge so that one end of the molecule has a slight positive charge and the other end has a slight negative charge. Nonpolar molecules do not possess this characteristic. Some polar molecules are water, ammonia, and hydrogen chloride. Some nonpolar molecules are methane, nitrogen and oxygen.

Since water is a polar substance, it tends to dissolve polar molecules better than it can dissolve nonpolar substances. This is why it can dissolve sugar (polar) and salt (ionic), but not oil (nonpolar). Nitrogen is a nonpolar molecule, so it will not dissolve well in water. Carbon dioxide is also a nonpolar molecule, so you might expect that it would not dissolve well in water either. However, something interesting happens when you dissolve carbon dioxide in water.

A carbon dioxide molecule can react with a water molecule to form a molecule called carbonic acid. Carbonic acid, which in solution is actually the carbonate or bicarbonate ion, carries a negative charge which allows it to dissolve in polar liquids like water.

[graham.d]

AS a real beer drinker I can't stand the use of a "sparklet" on a pump that seems to have the effect of introducing air (ie mostly nitrogen) into the beer. It fizzes it up to produce a light head with fine bubbles which some people find attractive and is more popular in the north of England. But, besides making it hard to pour, it seems to have the effect of flattening the beer more quickly. I think this may be that the nitrogen bubbles somehow are nucleation centres for the CO2 and causes a more rapid flattening as a result. To me this spoils the taste too but others disagree. However, does anyone have any better explanation as to the change in the beer as a result of the use of the nitrogen, or even comments on the qualities of beer as a result.

[chris]

Hi Graham

this is absolutely right. The introduction of the nitrogen (or any) bubbles helps to pull the dissolved CO2 from the liquid. This is essentially how the famus "coke and mentos" experiment works - the mints have tiny bubbles trapped in their surfaces. When the are added to the liquid the small bubbles act to seed the formation of larger bubbles using the gas from the drink. The resulting eruption is quite impressive, but the resulting liquid left behind is definitely disgusting!

Chris

[Make it Lady]

Try putting salt in a can of fizzy drink if you can't find mentos. Great cafe trick to play on someone you don't like.

[techmind]

Paul asked the Naked Scientists:
Question: Why do we use carbon dioxide in the fizzy drinks? Could it be another gas, say nitrogen?

Certain beers (including Guinness, and other "cream flow" or "smooth flow" bitters) are served Nitrokeg. These use nitrogen which (I guess coupled with the foaming properties of the drink) produce a fine-bubbled smooth head - without the fizzy sensation.

Google for Nitrokeg will give a lot more information - much of it strongly-held opinions!

[lyner]

Carbonating is something you can do at home -brewing.
We have developed a taste for it. Champagne is the ultimate fizz and you couldn't get it to look like that with N2.
In any case, it just isn't convenient to put N2 bubbles in at home and that's no great loss to mankind. It's pretty inert and tastes it too!

[rawraj]

I had the same question but I was wondering why not use oxygen??
It would be a healthy fizzy drink. What is stopping the production(product) of an oxygenated fizzy drink?
There is a bottled water called oxyrich available in my city.
They claim that they have a unique filtration process that adds 300% more oxygen to the water.
I have to tell their water is strikingly more refreshing that normal water(or other brands).
Its not psychological. Normally in my city it is hard to be loyal to Brands in bottled water, because shop keepers just keep the brand that was the best sales man at that time. Even though I used to drink only aquafina(Pepsi brand) was forced to drink this when it was first introduced in the market.
It was after drinking it for the umpteenth time and feeling "power charged" I decided to check the label and thus read the info.

[geo driver]

when making our cream flow beer at work we use 'mixed gas' which is a mix of co2 and n2.  this makes the wonderful creamy head.  you have to be careful when pouring the real beers without a sparkler as you may find that the beer can taste bland (with out life).  Conditioning is very important, keged ale continues to ferment which is why it has to be kept cold so the yeast dont like it.

i keep the beer in 800lt pressurised conditioning tanks. filled with beer and yep co2, this increses the time i can keep it for b4 it goes off. but it is kept at atmospheric pressure and no carbonation stone is used so it stays the right consistancy

at the same time if you want a proper beer "home ish brewed" with out the sparkler look me up

trust me its great and the trick if you want a beer to stay fizzy is just to drink it faster

[geo driver]

another thought.  the liquid on the inside of a coke can is not fizzy. its only when it come into contact with the air that the co2 is relised

[rosy]

another thought.  the liquid on the inside of a coke can is not fizzy. its only when it come into contact with the air that the co2 is relised

Not contact with air, but the release of pressure.
CO2 is (gases in general are) much more soluble in water if there is a high gas pressure in the space above the drink, basically because there's less "space" for the gas to escape into. (Actually, of course, it's an entropy thing, but I don't have the time to explain that here...).