Carbonating beer is one of the final steps in the brewing process and is an important flavor component in beer. It adds effervescence and life to beer. We can taste the Carbon Dioxide that carbonates beer as sourness, http://www.scientificamerican.com/podcast/episode.cfm?id=carbonation-has-a-taste-09-10-16. The carbonation contributes to perceived “fullness” or “body” and enhances foaming potential of beer. The Carbon Dioxide bubbles enhance the aroma of beers. Carbon Dioxide also plays an important role in extending the shelf life of beer. There are two ways to create and control the amount of carbonation in beer, bottle conditioning and force carbonation. Either unfiltered wort or filtered wort that has been reseeded with yeast can be used to bottle condition or naturally carbonate beer. A variety of sugars, additional wort, or malt extract can be added to the beer and then placed in a sealed bottle to “referment.” As CO2 is created by the yeast, it is adsorbed into the beer. Last month, Scott Burns described his procedures for sanitizing and getting bottles ready for bottle conditioning. There are a number web sites that provide detailed steps for naturally carbonating beer. Several of these sites are:http://drinks.seriouseats.com/2011/02/homebrewinghow-to-carbonate-and-bottle-your-beer.html,http://www.howtobrew.com/section1/chapter11.html and http://www.northernbrewer.com/learn/homebrewing-101/step-4/. To complicate matters, not all beer styles taste good at the same carbonation level. The amount of carbonation in beer is measured in volume of carbon dioxide per volume of beer. Milds – for example – taste better at about 1.64 volumes while wheat flavors of a Wiezen taste best at a volume of around 2.5. There are a number of calculators to assist you in determining how much sugar is needed to bottle condition different beer styles including
http://www.northernbrewer.com/priming-sugarcalculator/and http://www.tastybrew.com/calculators/priming.html. Force carbonating beers requires a kegging system to infuse carbon dioxide under pressure. The temperature and amount of pressure to the beer play important roles in determining CO2 concentrations in the finished beer. The lower the temperature of the beer, the easier the beer can absorb Carbon Dioxide. The procedures for force carbonating beers can be found at http://blog.brewps.com/2012/04/homebrew-kegcarbonation-chart-how-to-force-carbonate-beer/ and www.youtube.com/watch?v=Y0GQOg5PyLY. When force carbonating beers, achieving the proper concentration of Carbon dioxide or volume for a beer style can be accomplished by creating equilibrium in between the amount of pressure being applied to the beer and ability of the beer to absorb the carbon dioxide. Fortunately, there are web sites like http://www.simgo.com/draft1.htm and
http://www.kegworks.com/faqs/Draft-Beer-Quality-Manual.pdf that calculate a beer’s final Co2 volume based on the pressure (PSI) and temperature.

Mel Thompson uses a PSI gauge attached to a corny keg fitting , to check the pressure of his real ales to assure that the pressure doesn’t exceed 10#. If the pressure starts to creep up above 10#, he de-gasses the keg to the appropriate pressure. During the secondary conditioning, he checks the pressure daily.