There’s something magical about the snap and fizz of opening a new bottle or can of beer. I especially love the deeper pop as the cork comes out of a cork and cage bottle. These sounds are thanks to beer carbonation and they prepare our entire sensory system for that liquid we love so.
Join me for a look into beer carbonation, nitrogenation, how carbonated beer styles should be, and why beer goes flat!
Before we get to the why of beer carbonation let’s get a simple what out of the way. Carbonation is dissolved carbon dioxide (CO2) in beer. The CO2 dissolves into the beer under pressure, then when you open the bottle the pressure inside is lowers and the CO2 comes out of solution resulting in wonderful scrubbing bubbles.
Why Do We Carbonate Beer?
We carbonate beer because of those wonderful scrubbing bubbles, not these scrubbing bubbles don’t drink them. According to Garret Oliver’s The Brewmaster’s Table,
The carbonation in beer lifts and scrubs strong flavors from your palate, leaving you ready to enjoy the next bite [of food] as if it were the first.
When CO2 hits your tongue it creates a nucleation site resulting in the familiar tingle we’re used to. Sometimes that tingle becomes a bite, the bite is from carbonic acid which gives the impression of acidity and increased bitterness.
How Do We Carbonate Beer?
Carbonation occurs naturally during the process of fermentation, from yeast eating the sugars in the wort. The CO2 from fermentation escapes the fermenter so the pressure doesn’t build up. If you go on a brewery tour and see plastic buckets bubbling away that’s the CO2 escaping. In order to achieve that tingly beer carbonation, the CO2 is added back in.
The traditional way to carbonate beer is to wait for primary fermentation to finish then add more sugar, specifically called priming sugar, and fresh yeast to create a secondary fermentation in the bottle. The CO2 in this secondary fermentation remains in the bottle and creates carbonation in the beer.
Bottle conditioning beer leaves you somewhat at the mercy of the yeast. Improper bottle conditioning is often why beer is flat. Breweries and homebrewers alike prefer more control and so they force carbonate the beer before packaging.
Force carbonating beer is adding pure CO2 into the beer to achieve the desired level of beer carbonation before packaging it. This is one of the reasons breweries use Brite Tanks – tall, flat bottomed vessels – like the one from FigLeaf shown below. Most breweries buy CO2 for this purpose, but some capture the CO2 that escapes during fermentation and add that back in.
Levels of Beer Carbonation
Most people measure the level of CO2 in beer as a measure of volumes of CO2. A volume of CO2 is about 1.96 grams per liter of CO2. On average Beer has 2.5 volumes of CO2 or 5 grams CO2 per liter. On the lower end of the scale are British Bitters, which are often poured from a cask and nearly flat, they clock in around .75 – 1.25 volumes of CO2. This is what the BJCP would classify as “low carbonation.” Jumping to the other side of the scale we have Belgian Gueuze beers at 3 – 4.5 volumes of CO2 or “highly carbonated” per the BJCP.
For a full list of styles and volumes of CO2 check out the drop-down box on TastyBrew.com. For comparison sake, Champagne has 6 volumes of CO2.
What About Nitro Beers?
Adding nitrogen (N2) to beer began with Guinness trying to package the mouthfeel being created in Irish pubs. After about 40 years, the use of nitrogen in beer has slowly spread to other stouts and porters and now to broader styles like IPAs.
According to The Oxford Companion to Beer, adding nitrogen to beer doesn’t affect the flavor but does create smaller more stable bubbles than CO2. These smaller, stable bubbles lend themselves to the thick, persistent stand of foam Guinness is known for. With the reduced carbonation there is less carbonic acid resulting in less acidity and bitterness, therefore smoother, creamier, and sweeter beer.
One last thing to note is that almost all tap lines use some blend of N2 and CO2 to move that beer. Too much CO2 will add more carbonation to the beer than the brewer intended.
Foam and Flat Beer
I started writing this post because of issues with local breweries bottling flat beer. I’m not going to say who those breweries were, this isn’t about throwing shade, just spreading education. Luckily, flat beer is pretty rare.
Beer goes flat when the yeast doesn’t eat all the priming sugar from bottle conditioning. Or if there isn’t enough yeast or priming sugar to begin with. Beer can also go flat by the slow release of CO2, from something like an improperly sealed cap.
When it comes to foam, you can have carbonation without foam, but you can’t have foam without beer carbonation. My plan was to get into foam more, but once I began my research I realized it is a far more complex subject that can be covered here. I’m planning to write another post on it eventually, for now, I leave you with this quote from Proof: The Science of Booze,
“98% of foam problems have nothing to do with the beer, only the way it’s poured.” – Charles Bamforth, Professor at UC Davis.