Another way carbonation is created inside beer is by inserting the gas under high pressure—referred to as pounds per square inch or PSI—in a sealed container (a keg for instance) until the liquid absorbs the gas. When the pressure is relaxed the CO2 separates as small bubbles, causing the liquid—in this case beer—to fizz, form foam atop the beer and release the pleasant malt and hops aroma from the key ingredients.
Carbonation is measured by the volume of CO2 in liquid. The volumes vary by beer style, but the majority fall in the 2.1 to 2.8 ranges with cask ales offering less and some German varieties, like a weissbier or a Belgian lambic, offering more.
The ubiquitous American light lagers, as a point of reference, carry a volume of about 2.6 volumes.
CO2 also plays a role in the dispensing of beer on draught. Currently there is a concentrated effort on behalf of America’s craft brewers to make sure that when a pint is poured the carbonation levels are what they should be. This ensures existing customers and newcomers alike get the full experience of an expertly made commercial brew.
Understanding the science is crucial and is a point of passion for many brewers, professionals and homebrewers who at one point or another in their career have struggled to keep the balance just right.
“The knowledge has changed in the last fifteen years,” says Chris Graham, the owner and partner at the Concord, CA-based homebrewing supply shop More Beer. He recalled his early days of homebrewing and how a pamphlet would say to set the CO2 to 20 pounds per square inch (psi) and then shake the keg.
“There was a lot of bad information on how to carbonate a beer,” he recalls. “I quickly learned that [technique] didn’t work.”
Now, there are a number of well-respected manuals, easy to use equipment and a greater respect overall to making sure carbonation is how it should be.