What is Carbonation?
How to Carbonate Liquids
There are three primary factors required in order to successfully carbonate a liquid. First the liquid must be cold, around 35° to 45°F (1.7° to 7.2°C). This will help with efficiency of absorption of the gas into the liquid. Colder liquids help the conversion from carbon dioxide gas to liquid carbonic acid. Second atmospheric pressure must be raised 15+ Pound Per Square Inch (psi) or more and maintained. Keeping the liquid above atmospheric pressure (1 atmosphere at Sea Level or 14.6959 psi) is essential to keeping the carbon dioxide in solution. Sometimes this is referred to as “high-pressure” especially when dealing with large volume containers. Third the carbon dioxide gas must be exposed to the liquid over time. Often this is done by infusing the gas through agitation or mixing. Carbon dioxide in a cold liquid and under pressure will convert to carbonic acid and remain as a liquid as long as pressure is maintained. It is essential to successful carbonation to keep all three factors in mind. After carbonating it is possible to allow the liquid to warm up however the pressure will increase. Also sudden agitation at high temperatures may cause the gas to nucleate out of the solution; quickly increasing the pressure beyond the containers capabilities.
There are two methods for carbonating beverages the first is known as natural. Natural carbonating occurs when carbon dioxide is formed or chemically introduced under pressure. Many carbonated waters are naturally carbonated deep below the earth's surface. Carbon dioxide is naturally present in rocks deep within the earth. Natural springs under pressure push and dissolve the carbon dioxide into its liquid. This often includes many hardening minerals and nutrients that flavor the spring water. If the pressure is maintained to the surface carbon dioxide will remain in the solution. Another form of natural carbonating occurs when a beverage is primed with a solution of sugar and yeast. The ensuing fermentation creates trapped carbon dioxide and quickly pressurizes the container. The carbon dioxide is forced into solution naturally; although many home brewers know this process can quickly get out of control or not occur at all. The unpredictability of natural carbonation has encouraged the second method known as manual carbonating (passive & direct diffusion). Manual carbonating occurs when carbon dioxide gas is diffused or mixed with a cold liquid mechanically. This method is more scientifically accurate in the amount of carbon dioxide dissolved into the solution. Almost all carbonated beverages on the market are manually carbonated. There are some exceptions with natural waters, homebrew and champagnes.
Understanding the Chemistry of Carbonation
The biochemistry of carbon dioxide is critical to all carbon-based life. This can be very confusing to the non-scientific layman. For our purposes here we will keep the vast subject narrowed to carbonating beverages. Very often you will find articles that will dive into the chemistry of carbonation. Understanding some of the basic terms is essential. One of the most common terms is nucleation. This is observed in bubbles of carbon dioxide rising to the surface. This off gassing occurs at room pressure. Carbon dioxide can come out of a solution by heterogeneous (forming from surfaces) or homogeneous (from impurities in the liquid) nucleation. Bubble size and quantity will vary according to the thickness (viscosity) of the beverage. The bubbles formed in a glass of champagne are very different from a glass of root beer. Carbonated water can also be deceiving in its appearance of bubbles. Pure water will show very little nucleation and hardened water will bubble like crazy. Do not allow your visual perception to determine carbonation levels. The amount of carbon dioxide in a solution is often measured in atmospheres (atm). This refers to the atmospheric pressure at sea level. We do not normally think about the weight of the atmosphere above us pushing down on everything. This atmospheric pressure has a lot to do with carbonating as it will keep the carbon dioxide in the solution or will allow it to nucleate out of the solution. Carbonation in atmospheres is determined by using a scientific method of taking a measured sample and knocking the carbon dioxide out of the solution. The resulting pressure is then charted to reveal its liquid atmospheric pressure. This atmospheric pressure is the carbon dioxide gas pressure in the liquid of a given sample. Many carbonated waters and soft drinks are carbonated above 3 atmospheres. All other beverages are usually below this extreme amount. When reading up on the subject try not to get confused between the amounts of atmospheres contain within a liquid and container pressure. Liquids can contain more carbon dioxide than exhibited in overall standing pressure.
Myths About Carbonation
There are many myths regarding carbonation. Hopefully this article will help dispel some of them. One of the biggest myths about carbonation is that you need extreme pressures to achieve it. Most breweries carbonate beer very efficiently in bright tanks under 18 psi. Defusing gas over time is the key to successful carbonation in a brewery. Bright tanks use a diffusion stone to mix the carbon dioxide into the solution slowly. This also helps "scrub" the beer of impurities and oxygen. In far smaller quantities the diffusion is done by shaking the container. An injecting and shaking method is far more efficient at dissolving carbon dioxide into the liquid than the use of mechanical diffusion devices. Higher pressure alone will not increase the amount of carbon dioxide absorbed. Continuous mixing/diffusion at low pressures are far more efficient. The quantity absorbed not the pressure of the inbound carbon dioxide is the key to success.
Carbonated beverages are bad for your health. - Actually scientific studies have shown that moderate consumption of carbonated water is far healthier than alternative carbonated beverages. This would seem like a "no-brainer" given that the alternative often has sugar and additives that increase your caloric intake. No matter which carbonated beverage you consume, most of the carbon dioxide will come out of solution during digestion. There have been some studies in the soft drink industry that have indicated that carbon dioxide effects tooth enamel. This study has been flawed by the quantity of amounts consumed beyond the normal human’s ability of consumption. Also the damage from high caloric liquids to tooth enamel has been ignored. Of course it's all dependent on quality and quantity. “Everything in moderation” is a motto to live by.
You can't taste the level of carbonation in beverages. - To some degree the human palate can detect levels of carbonation with years of experience. Most cannot detect levels beyond 3 atmospheres as the amount of off gas created by nucleation points within the mouth; "Just too foamy to tell". Many experienced beer judges (BJCP) know the proper level of carbonation within a given sample by taste.