Natural Carbonation in a Keg (How To Do It & How Long To Wait)

Carbonation is the last (but not least!) step of the brewing process and has a tremendous influence on the profile of the beer. Natural carbonation is a traditional, proven process, but requires more patience than modern alternatives, but what’s the difference?

Natural carbonation occurs during the fermentation process, when yeast consumes sugar, producing carbon dioxide. In an enclosed fermentation, the carbon dioxide remains trapped, saturating the beer and becoming carbonic acid which adds the pleasant fizz to your beer. The process takes two to three weeks and can be achieved in a variety of ways.

Keep reading to learn more about natural carbonation, and how to achieve it in your kegged homebrew.

What is carbonation?

Carbonation stimulates something called the trigeminal nerve found in your mouth. The purpose of the trigeminal nerve is to sense hotness, coldness, or irritants.

In the context of beer, highly carbonated brews are said to have a slight burning sensation, sometimes called a carbon dioxide “burn.” When a beer is properly carbonated, you should just feel a pleasant tingling sensation, similar to what you’d feel when drinking a carbonated (non-alcoholic) soda.

Carbonation can have a noticeable impact on beer flavor. By stirring volatile aroma compounds in the beer, carbonation helps make them more detectable. In addition to promoting flavor compounds, carbon dioxide influences the top-foam and creamy mouthfeel associated with a good, foamy beer. Carbonation is essential to the brewing process to create a refined result. 

Carbonation – as the name suggests – is the volume of carbon dioxide contained within a liquid. The greater the amount, the more carbonated the beverage. On average, an English cask beer has about 1.5 volumes of carbon dioxide, whereas champagne has about 7.0 volumes of carbon dioxide. 

The amount of carbon dioxide in a solution is inversely proportional to the temperature of the solution, which means that the colder a solution is, the higher the concentration of CO2

What is carbonation in beer?

Natural carbonation occurs when yeast converts sugars into carbon dioxide.

Inside the fermentation vessel, the carbon dioxide has nowhere to escape, so it saturates the beer and transforms into carbonic acid (the liquid form of CO2). That carbonic acid then binds to the flavor and aroma compounds in the beer.

Once natural carbonation has occurred and the keg or bottle is unsealed, carbon dioxide rises to the surface and tries to escape. That’s why you see those tiny bubbles rush to the surface of the beer.

Effective natural carbonation creates tiny bubbles, resulting in a fine head to your beer. Natural carbonation can also result in a softer, rounder taste profile in the beer.

Natural carbonation is an age-old carbonation method. Before modern-day brewing equipment, breweries waited patiently for natural fermentation to do the work. It is a simple, but effective method of adding carbon dioxide to your beer. The fermentation process is nearly 10,000 years old, commonly mostly used in the creation of wine and beer.

Fermentation is a chemical process by which glucose and other molecules are broken down anaerobically. The process not only produces alcohol but also carbon dioxide, as yeast digests the sugars in the wort. As a result of the fermentation, a large quantity of carbon dioxide is liable to escape, so the brewer seals the beer in a container towards the end of the process.

Some homebrewers employ another method for natural carbonation in smaller quantities. In this method, the beer is allowed to ferment completely, unfiltered with active yeast still floating inside. The brewer needs only to add a small amount of sugar at bottling time. Once the bottles are firmly sealed, the yeast continues consuming the added sugar, releasing fresh carbon dioxide in the process.

Can you carbonate a keg naturally?

You can carbonate a keg naturally, but most brewers do not choose this method.

Nowadays, it is relatively uncommon to carbonate an entire keg naturally. However, the process is possible and uncomplicated.

Here are some of the reasons why you might choose natural carbonation:

  • Homebrewers who prefer natural carbonation over forced carbonation say the natural carbonation results in a thicker head, smaller bubbles, and more lacing (the ring of foam around the glass that remains after the head dissipates).
  • Natural carbonation requires less equipment than forced carbonation. Those who are just starting their homebrewing journey should choose natural carbonation. It is notably cheaper, but you will have to wait longer to carbonate your beer.
  • Most brewers regard natural carbonation as a traditional method. For this reason, some brewers prefer to go “all-natural.” Since the method has been utilized for such a long time, there are countless tips and resources for reference. 

How long does natural keg carbonation take?

There is no strict value, but the general consensus suggests a timeline of 2-3 weeks

Can you use a keg without CO2?

Using a keg without carbon dioxide is a big no-go.

While it is possible to keg beer without a carbon dioxide setup, beer served without it will spoil much more quickly.

Do not be misled into believing that you can naturally carbonate a keg and serve the beer without a kegging or carbon dioxide setup. The right kegging equipment is of paramount importance.

How to naturally carbonate a keg of homebrew beer

Natural carbonation is when you carbonate a keg of homebrew with sugar. It takes longer than forced carbonation, but the process remains straightforward.

To naturally carbonate your homebrew keg, you will need to:

  • Calculate your priming sugar amount
  • Mix priming sugar into the beer
  • Pour the water into your homebrew keg
  • Set up your fermenter
  • Let your kegged beer condition
  • Refrigerate your kegged homebrew
  • Attach the keg to the carbon dioxide and serve

Calculate your priming sugar amount

You will need to determine how much carbon dioxide you want in your brew. If you are new and have no idea of the correct amount, aim for about 2.3 to 2.5 vols of CO2.

You can also refer to a carb calculator online. Or try this priming sugar calculator to determine the correct amount of corn sugar or DME.

Mix priming sugar into the beer

After you have determined the right amount of priming sugar, heat about a pint of water in a saucepan, in which you dissolve priming sugar.

Mix in your priming sugar and heat the water to a boil. Set the water aside to cool.

Pour the water into your homebrew keg

Once the water has cooled to room temperature, pour the water into your homebrew keg.

You should take care that the keg is clean and sanitized to avoid contamination.

Set up your fermenter 

Next, rack your homebrew from the fermenter to the keg.

This step requires additional equipment, namely a siphon

Let your kegged beer condition

Make sure to properly seal the keg to contain the carbon dioxide (and to exclude contaminants).

Refrigerate your kegged homebrew

Once the keg is sealed, you should leave the keg at a cool temperature. You can refrigerate it if you have the capacity.

If not, leave it in a cool room for about two weeks. Place the keg in a space where the temperature remains steady.

Fluctuations in temperature can stall your yeast or otherwise impede the process. 

Attach the keg to carbon dioxide and serve

Before serving your beer, you will still need some carbon dioxide in the mix.

I recommend adjusting the regulator pressure to 10 PSI for serving.