Lie — Pumping air into a soda-pop bottle will keep it from going flat

The Story

The Original Fizz-Keeper Pump Cap has sold over one million units! Patented pump cap keeps re-pressurizes soft drinks using a simple effective pumping motion. Keep those big liter bottles of soda as fresh as they day you bought them!

The above ad for the Jokari Fizz-Keeper Pump Cap describes just one of many similar products for keeping carbonated beverages from going flat. Some will even work with sparkling wines using the same principle.

Cans and bottles of carbonated soft drinks are normally pressurized to about twice standard atmospheric pressure, but once they are opened, this pressure is lost. Replacing the bottle cap prevents any further loss, yet much of the carbon dioxide will soon bubble out of the liquid in order to restore the air pressure inside the bottle.

This product allows one to pump air into the bottle and restore the original two atmosphere pressure. That means that the CO2 will no longer leave the liquid, and the beverage will retain its bubbles.


The facts stated above are true, all except for the most important one, the last sentence.

When a gas and a liquid are in contact, two processes happen at the same time: some of the gas will dissolve into the liquid, and some of the gas that is already dissolved in the liquid will be released. The more gas that is dissolved, the faster the rate of release. The more gas pressure in the air, the faster the rate of absorption. Eventually these rates reach equilibrium, with the amounts entering and leaving the liquid being the same.

If there is more than one type of gas involved, this same process happens with each one, independently of the others.

Consider a bottle containing a liquid that has a lot of dissolved gas A and a little gas B, with air at the top containing a little A and a lot of B. Gas A will be released from the liquid until it reaches an equilibrium. Gas B will be absorbed by the liquid until it reaches an equilibrium.

Each of these gasses are affected independently, one perhaps happening quickly, the other taking much longer. The only time multiple gasses should ever be considered at the same time is when calculating the total pressure in the bottle, which is simply the sum of the partial pressures provided by each individual type of gas.

Now consider the case where the bottle has a lot of dissolved CO2. It is only the partial pressure that is important, so in order to quickly achieve equilibrium to keep the liquid from going flat, the partial pressure of the CO2 must be increased to what it was in the unopened bottle.

Air normally contains about .04% carbon dioxide. So to get the 2 atmospheres of CO2 pressure that was originally in the bottle, enough air would have to be pumped into the bottle to provide 5000 atmospheres of air pressure. This is equivalent to the pressure more than 30 miles deep in the ocean, which is 5 times deeper than the deepest ever discovered. This pressure is 20 times what a scuba tank normally holds.

Using the advertised hand pump to restore the original 2 atmospheres of pressure will increase the CO2 content from .04% to .08%. This very small amount will have an insignificant effect on the beverage's carbonation. For all practical purposes, it will go flat just as quickly with or without the use of this amazing device.

If you pour a cup of drink from a bottle and use the pump to represurize it, it really will reduce the loss of CO2, but only by about one bubble's worth.

(There are devices that can be used to pump pure carbon dioxide into wine bottles. These really do work, but for ordinary soft drinks it would be far cheaper to buy a new bottle.)


Over a million of that one brand of gadget have been sold. Their pressurization claim sounds reasonable (unless one remembers grade 9 chemistry or physics), so some people believe the lie, while other people get rich.