Carbonation Techniques

Fast and Furious–>Quick CO2  |  PressForce Carbonation  |  PressKraeusening
PressSpunding  |  PressBottle Conditioning

One of the main features that distinguishes beer from all other beverages is its ability to pour a nice thick, foamy head. Indeed, without those millions of tiny bubbles, a beer would seem lifeless and dull. When beer is properly carbonated it will most fully express its aromatic qualities and it will tingle and effervesce in the mouth. To better understand this crucial element of beer, we should examine just exactly where all those bubbles are coming from.

Yeast is the life force in beer. When yeast is pitched into brewer’s wort it feeds upon sugars and gives off equal parts of alcohol and carbon dioxide (CO2). The amount of C02 given off by fermentation is considerable. Most of this is simply vented off the top of the fermenting vessel (except in large breweries where it is collected, cleaned, compressed into a liquid and stored for later use).

To carbonate their beer, brewers have a variety of techniques available. This article will discuss the following methods: bottle conditioning (priming), spunding, kraeusening, and force carbonating.

Bottle Conditioning

One of the oldest methods of carbonating is called priming. This traditional ale making method involves letting the beer ferment out and then racking it into kegs or casks. At this point a small dose of sugar is added to each cask. The remaining yeast in the beer ferments this sugar and the beer retains the C02 generated.

Priming is also the most popular carbonating method with home brewers, especially those just beginning to home brew. The normal recommendation is for 2/3 cup of corn sugar to prime 5 gallons of beer, (editor’s note: some guides will say up to 3/4 cup of corn sugar to prime; experience dictates closer to 2/3 cup for proper carbonation levels). The sugar is mixed into the beer just prior to bottling. After 2 to 4 weeks in the bottle, the beer is usually ready to drink.

Those who age their beer for extended periods before bottling can run across the problem of having very little active yeast left over to prime the beer properly. Beers over 8% alcohol can have this problem also. The solution is to pitch a small dosage of new yeast along with the priming sugar. This yeast does not have to be the same strain used in fermentation. Lager yeasts are sometimes used for bottle conditioning because they tend to flocculate better than ale strains.

One of the greatest advantages of bottle conditioned beers is their potential shelf life. Provided they are properly handled, beers with active yeast in the bottle can continue to mature and develop for months or even years. Filtered beers do not have this advantage.

Bottle conditioning is no guarantee of long term stability, however. Excessive amounts of trub or non-viable yeast cells in the bottle can lead to adverse flavor changes and actually shorten the potential shelf life. For this reason most commercial breweries will filter their beer after aging and then pitch a known quantity of priming sugar and yeast immediately prior to bottling. This helps ensure that the product will be fairly clear in the bottle and that the amount of sediment will be within reasonable limits. Indeed, when properly performed, this procedure can give such low amounts of sedimented solids that the consumer might be unaware that the beer is bottle conditioned. The ales from Sierra Nevada Brewing Company are a good example of this procedure.


Another method of carbonation is called spunding (sometimes referred to as bunging). In a single tank system this method simply involves closing the tank vent when fermentation is within 1% Plato (.004 gravity points) of its completion. The remaining C02 generated is retained in the tank and absorbed into the beer.

In a multi tank system the beer is fermented down to within 1.0-1.5% P of its target gravity (usually in an open fermenter) and then transferred to the secondary fermentation vessel which is capable of holding pressure. A disadvantage of this method is that by removing the beer from its yeast bed an incomplete attenuation can result. This is normally offset by the rousing of the yeast caused by the turbulence of transfer. Home brewers should simply make sure they siphon up a bit of the yeast bed during transfer.

Obviously, spunding is most commonly used by lager brewers. The slow fermentation times of lager beers make it easy to predict when the desired Plato reading will be reached. Some breweries might have lager beers usually show a drop of 1% P per day for the last 3 or 4 days of fermentation. Ales, on the other hand, will sometimes drop 2 to 3 % P within an 8 hour period.

For the home brewer the same rules apply. Spunding would be most practical for someone who brews lagers in 5 or 10 gallon soda kegs. When the fermentation is near completion the vent should be, closed.. and a pressure gauge attached to the gas inlet connection. This will allow monitoring of the pressure build up. Most soda kegs will hold up to 130 psi but if you should ever find yourself with 30 or so pounds of pressure in your tank after spunding you will know that something has gone wrong. Commercial breweries have pressure relief valves set at 12 to 15 psi to prevent this. The home brewer will have to do this manually unless some sort of relief valve is incorporated onto the keg. Under no circumstance should this method ever be attempted with glass carboys or any other non pressure rated vessel!


Another method commonly used in lager breweries is kraeusening. This involves letting the beer ferment itself out completely before transferring to a lager tank. In the lager tank an addition of 10 to 20% new beer in high fermentation is introduced. As this additional beer ferments out the C02 generated is absorbed and carbonation is achieved. One of the main advantages of this method is that by blending between batches greater uniformity is assured. A major disadvantage is that the introduction of new beer into older beer can impart a “green beer” flavor which requires additional lagering time to be reduced.

The home brewer can utilize kraeusening more readily than spunding. Because the beer is fermented to completion, this method can also be used for ales. The only drawback is that one needs to brew an identical or very similar style of beer to act as the kraeusening agent.

One way to avoid this problem is by putting some unfermented wort aside and reintroducing it into its – parent batch after primary fermentation. Charlie Papazian covers this well in his book The New Complete Joy of Home Brewing, as does Douglas Serrill in zymurgy vol. 16, no. 5 (Winter 1993). They cover the appropriate calculations for the amount of wort to set aside. Usually it is about one quart for every five gallons of beer. The problem with this approach is the possibility of contamination from the storing of unfermented wort and its subsequent addition to the main batch of beer. Most home brewers get the best results by keeping beer transfers to a minimum, thus avoiding oxidation problems and possible microbial infection.

Force Carbonation

With the foregoing in mind, it is appropriate to consider a couple of final carbonation techniques. Force carbonation, as the name implies, involves forcing C02 gas into flat beer. Commercial breweries use a carbonating stone made of porous rock or sintered stainless steel to diffuse the gas into millions of tiny bubbles which are readily absorbed by the beer. The gas absorbs much more readily at colder temperatures. Trying to force up warm beer usually results in a foamy mess. [Keg beer usually is best at 2.4 to 2.6 volumes, bottles at 2.7 to 2.9].

Home brewers can force carbonate by racking their beer into a soda keg and then vigorously agitating the keg while forcing C02 into it. A more refined approach is to fit an aquarium aerating stone inside a keg. This serves as an effective C02 diffuser and can save your back the hassle of shaking kegs.

To demonstrate the ease of force carbonation we will take 5 gallons of beer that is flat and force it up to a proper dispensing level. The procedure is as follows:

1. Sanitize carbonation tank and purge with C02.
2.Transfer flat beer into carbonating tank using C02 pressure.
3. Attach C02 gas connection to carbonating stone.
4. Select appropriate pressure based upon temperature of beer.
5. Pump in C02 until gauge on top of tank reads the proper pressure. This takes about 60 seconds with most units.
6. Transfer beer back to original keg under counter pressure.
7. Dispense and enjoy!

OR …Fast and Furious Style

1. Sanitize carbonation tank and purge with C02.
2.Transfer flat beer into carbonating tank using racking cane, and some gravity, then seal keg.
3. Attach C02 gas connection to “in”. (Select appropriate pressure based upon temperature of beer).
4 Pump in C02 until gauge on top of tank reads the proper pressure. I generally force at approximately 12-15 # pressure. (A little higher pressure for quicker forces).This takes about 20-30 seconds with most units/regulators.
5. Shut off gas source, and remove gas line from keg.
6. Shake entire keg as vigorously as possible! Don’t hurt yourself. (I like a good 15-30 second shake).
7. Repeat steps 4-6 several times (Again depends on the beer style, but usually at least 5 times).
8. Let beer chill, and CO2 dissolve into solution for at least a full hour or two, (Better yet, a couple of days for the CO2 to dissolve and reach an equilibrium). This may take a little practice, but I can remember many a pre-party shakefests.
9. Dispense,…adjust if you must, and then enjoy!

As an aside, an additional benefit of a carbonating stone is the ability to scrub unwanted volatile aromas from your beer. For example, if you made a Pale ale and threw in a few too many handfuls of Cascade hops at the end you do not have to live with a beer that smells like grapefruit. Just turn on the C02 stone and leave the top vent open for a few minutes. The stream of gas rising through the beer will scrub out much of that overly hoppy aroma. Sorry, but it will not do anything about oxidation problems.