Beer styles and relative CO2 levels
Saturday, May 16th, 2009To begin, consider a brief refresher from chemistry class. Gases dissolve into liquids; the amount of gas that can be dissolved into a liquid is inversely proportional to that liquid’s temperature. At one extreme, boiling liquids contain very little dissolved gases; most home brewers know this, either directly or indirectly from having to oxygenate their boiled wort before adding yeast. But there are two other stages where we have to consider carbonation levels & temperatures.
The classic axiom for bottling home-brewed beer is ¾ cup of dextrose / corn sugar (or 1 cup of malt extract, or ½ cup of honey) for a 5 gallon batch, leaving 1-2” of air at the top of the bottle, regardless of size. Home brewers are strongly urged not to exceed that amount of sugar, as too much sugar leads to excess pressure and potentially exploding bottles. This one-size-fits-all approach will work for novice and intermediate home brewers, but for more exotic beers, or for more advanced brewers, there is room for more variation.
First, consider the style of beer. Most European Lagers and American Ales have the same carbonation levels, but there are exceptions. Porters & Stouts, along with British ales, tend to traditionally have lower carbonation levels, with Belgian ales lying between the Porter/Stout and the American/European beers. A few beer styles, such as fruit Lambics and German wheat beer, have very high carbonation traditionally.
Next, consider the bottling temperature of the “green” (uncarbonated) beer. A colder bottling temperature means more CO2 is dissolved in the beer. A “green” Lager kept at 40 degrees F will have almost 50% more CO2 already dissolved than a “green” Ale kept at 60 degrees F, which goes a long way towards explaining why a finished Lager often has more foam than a finished Ale.
Finally, consider carefully modifying the type amount of bottling sugar. Because even small changes can result in a big difference, consider using dried malt extract, or even liquid malt extract instead of sucrose, as these types of sugars are less efficient for the yeast, and gives you the brewer a little more room to work within. Since few home brewers attempt Lambic-style beers, mostly you’ll be reducing the amount of bottling sugar for your Belgians, Porters, Stouts, and British Ales by a few teaspoons, down to an absolute floor of ¼ cup of dry malt extract for a 5 gallon batch.
There is another way to modify the amount of CO2 in bottled, home brewed beer. Leaving less air in each bottle causes pressure to build up more quickly; increased pressure results in reduced yeast activity, and thus less CO2. Conversely, leaving more air in the bottle will cause faster fermentation and more CO2, but more pressure inside the bottle means more risk of exploding bottles, and safety has to be a priority in this case.
There’s something here even for the non-brewers: what temperature is best to serve beer at? Remember, the temperature of the beer determines how much CO2 is dissolved, and how much foaming will occur. Beer styles with less CO2 can be served at a higher temperature, because there’s less CO2 dissolved in the beer; serving these beers at a colder temperature means more of the CO2 is dissolved, and less will be available to provide effervescence and foam. A Stout served at near-freezing temperatures will fail to produce a solid head, and may even taste flat. Conversely, a Lambic served at room temperature will bubble & foam like champagne or worse. This is why many of the English bitters are served at ‘cellar’ temperature (55F), which is warmer than fridge temperatures.
