Carbonation is a phenomenon in which carbon dioxide gas is suspended in water, creating small bubbles. It can occur both naturally and artificially, as a result of the introduction of carbon dioxide to a liquid. This phenomenon is what makes soft drinks bubbly and fizzy, although the fizzy sensation is actually not caused by the bubbles themselves, but rather by the chemicals which make the bubbles.
There are a number of reasons for people to use carbonation in the preparation of beverages. One thing about carbonation is that it drives out the oxygen, which can make a beverage shelf stable as long as it is sealed, keeping microbes which need oxygen to survive out. Many people have also noted that carbonation adds to flavor, as seen when someone drinks “flat” soda which has been opened and left out, allowing the carbon dioxide to escape. The soda tends to taste boring and less dynamic without carbonation.
Historically, carbonation occurred naturally in many fermented beverages like beer, because carbon dioxide is a waste product produced by the yeasts which are an integral part of the fermentation process. Carbonation is also the process behind the holes which appear in cheese and bread, incidentally. The amount of carbonation which occurs can be controlled, to some extent, and sometimes more is added by modern breweries. The carbonation explains why beer needs to be kept under pressure, so that the gas will not escape.
The effects of consuming carbonated drinks on the body can vary. Much of the carbon dioxide actually escapes before it enters the digestive tract, in the form of burps. CO2 which manages to reach the intestines is quickly absorbed, and as a result, can promote quick absorption of other things in the digestive tract as well. This is one reason fizzy drinks appear to “go to the head” so quickly, because the CO2 actually promotes the absorption of the alcohol. The carbon dioxide absorbed by the body is eventually expressed by the lungs.
Some people have claimed that consuming carbonated drinks will have deleterious health effects. Given that humans have been drinking carbonated fluids for a very long time, these claims should be taken with a grain of salt. In fact, consumption of drinks with carbonation is sometimes recommended for people who are feeling nauseous, illustrating that it can have some benefits, and drinking carbonated water while traveling can protect against some microbes found in water, since they cannot survive in properly carbonated water.