The Ultimate Guide to Carbonation
Forced and Natural Carbonation: The Basics
Carbonation is an extremely important part of the brewing process. It has a direct effect on a beer’s presentation, mouthfeel and taste/smell.
This article will take you through each of the most common carbonation methods, forced and natural, the pros and cons of each, along with actionable steps to help you get started.
This intermediate-level guide designed for small and independent breweries, as well some helpful takeaways for home brewers.
How Does Carbonation Affect Beer?
Correct carbonation is an essential aspect of brewing the perfect beer.
A watery, dull, flat, lifeless drink is made lively and fresh with carbonation. It gives beer its bubbles, fizz and lightness and it also increases its shelf life.
On the other hand, over carbonation can hide the more complex flavours of beer and rapid carbonation can cause excessive foaming and breakout when bottling.
Along with carbonation, serving temperature is another key attribute that affects the flavour of a beer. Every beer has an ideal carbonation level and serving temperature.
For instance, dark maltier ales with complex flavours and full mouth feels should be served warmer than a more highly carbonated lager.
What is Carbonation?
When C02 (carbon dioxide) dissolves in beer (or other aqueous solution), it is called carbonation.
And carbonation is ruled by Henry’s Law, which states that:
“At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.”
The partial pressure of the gas above the beer has a direct effect on the solubility of gas in the liquid.
Temperature, pressure and beer composition affect the amount of C02 in a beer and, importantly for brewing, C02 is dissolved more easily into beer which has a lower temperature.
What are C02 Volumes?
The amount of C02 in beer is often expressed as “C02 volumes” or “volumes of C02”.
This is the space that C02 would occupy at atmospheric pressure and 0°C if it was removed from the beer.
- If the C02 was removed from 1 gallon of beer at 2.5 volumes of C02 at atmospheric pressure and 0°C, it would be 2.5 gallons.
- If the C02 was removed from 1 gallon of beer at 3 volumes of C02 at atmospheric pressure and 0°C, it would be 3 gallons.
It’s imperative to have equilibrium conditions and accurate instruments must be used, in order to measure C02 levels correctly.
What Affects Carbonation?
Pressure and temperature both affect solubility. Solubility increases with higher pressure and decreases with higher temperatures.
In terms of temperature, the following holds true:
- Colder temperatures: C02 solubility increases
- Warmer temperatures: C02 solubility decreases
The colder the beer is, the quicker the C02 is absorbed into the solution. This means it’s quicker carbonation and more efficient use of C02.
Ideally, when doing forced carbonation in a tank, you should aim for as cold temperatures as possible, with the optimum around 30 - 32°F.
Carbonation Level Reference Chart
The carbonation level reference chart provides an estimate of the required pressure to achieve a C02 volume at a specific temperature at equilibrium.
Follow these simple steps to estimate the required pressure to achieve your desired C02 volume:
- Once you know the temperature of your beer, find it on the left-hand side of the chart
- Along the same row, find the C02 volume you would like
- Look up the column to find out the pressure that will achieve that level of carbonation
- Use the pressure gauge on the tank to measure the head pressure.
- You’ve reached equilibrium when the head pressure is the same as the pressure being added by the carbonation stone and there is no more gas dissolving into the beer.
Types of Carbonation Stones
Using a carbonation stone you can carbonate a full batch of beer in a brite tank.
Carbonation stones increase the surface area contact with the beer and produce small C02 bubbles, which are easily absorbed in the beer.
A carbonation stone is made from either 316 sintered stainless steel or ceramic, which both work to effectively diffuse the C02 into the beer.
Ideally, the carbonation stone is fitted as low as possible in the brite tank in order to increase the distance to the head.
While they are typically connected to a brite beer fermentation tanks, via a tri-clamp,, some brewers use them in conical fermenters instead.
Wetting Pressure of a Carbonation Stone
All carbonation stones have a “wetting pressure”, which is defined as:
“The amount of pressure required for the C02 to pass through the pores of the carbonating stone and begin to make bubbles.”
In general, the wetting pressure of a carbonation stone is between 2 - 8 psi, but ceramic stones tend to have a higher wetting pressure.
How to Calibrate a Carbonation Stone
As we’ve already discussed, it’s imperative to have equilibrium conditions and accurate readings.
This means it’s important to understand the pressure required to start the bubbles and also the pressure required to make the bubbles stop.
To calibrate your stone, follow these easy steps:
- Attach the carbonation stone to your CO2 regulator
- Put the stone in a bucket. Make sure the stone is positioned in the same way it will be when it is in the tank.
- Gradually increase the pressure on the regulator
- Continue increasing the pressure until you begin to see a small trail of bubbles coming out of the stone
- Confirm the pressure on your regulator — this is the "wetting pressure" of the stone. It is usually somewhere between 2-8 psi.
- Slowly stop the pressure until the bubbles stop. At this point, record the pressure for a second time.
When you are conducting the steps above, check for any leaks around the stone. If you notice any, it’s important to fix the issue and then redo the test.
Now you know the wetting pressure of your stone, the next consideration is the effect of the static pressure of beer. The more liquid above the stone, the more pressure on the stone — this affects the wetting pressure.
Every 28 inches of liquid above the stone means an additional 1 psi of pressure. To calculate your static pressure, you need to know the distance from the carbonation stone to the liquid level on your sight glass.
Here’s an example:
- The top of the beer is 56 inches above the stone
- This adds 2psi to the pressure
- If the stone has a wetting pressure of 4psi and the liquid height is 56 inches, the total pressure is 4psi + 2psi. Or 6psi in total.
Or, in other words, you need 6psi of pressure from the regulator to generate a trail of bubbles from the carbonation stone.
Once you’ve reached equilibrium, leave the carbonated beer in the brite tank for a day or two, allowing the C02 to bind to the beer and improving head retention.
How to Operate a Carbonation Stone
When you start the carbonation process, the pressure difference between the stone and the headspace in the tank should be low.
Air can be picked up during the transfer, filtration or transfer process, and allows for any unwanted air to be dissolved.
However, don’t go overboard. This can cause the beer to lose some of its flavours and creative excessive foaming.
The whole process can take as little as a few hours, up to several days. Throughout the process, use high-quality gauges, check your tank to ensure the correct carbonation levels.
For better results, do not carbonate too rapidly as this can cause severe issues in the quality of the beer. Rapid carbonation can cause foaming, loss of flavour, reduced quality and inconsistent results.
Instead, follow a step carbonation process, as this will yield the best results. Step carbonation simply means increasing the pressure in small increments every half hour or so.
Carbonation Stone Best Practices
- Use a clean carbonation stone which makes tiny bubbles
- Do not overfill your tank — leave 15 - 20% headspace
- Your beer needs to be cold, but not frozen — aim for a minimum of 28°
- If excessive pressure is used, this can cause the stone to be ineffective
- Check for any leaks around the stone. If you notice any, it’s important to fix the issue and then redo the test.
- To eliminate C02 scrubbing issues, follow a slow, step carbonation
- Remember the figures in the chart are based on sea level. If you are above sea level, you need to add 1 pound of pressure for every 2,000 feet.l
Natural Carbonation: Spunding and Krausening
Naturally carbonated beers often have brighter flavours and a more consistent mouthfeel. There are two main techniques to natural carbonate beer. These are called Spunding and Krausening.
Spunding means bunging the fermentation to allow the C02 produced during carbonation to naturally carbonate the beer.
Basically, the process of spunding means closing the primary fermentation tank to trap naturally occurring C02 gas by the yeast at the tail end of fermentation.
A spunding valve is attached to the tank late in the fermentation (when most of the sugars have been processed by the yeast).
The valve then controls the release of C02 in order to keep the tank pressurised and to produce the desired carbonation and mouthfeel.
How Does Spunding Work?
Spunding is often used by larger brewers as a way to naturally carbonate beer and it’s arguably the easiest way to naturally carbonate beer.
The steps behind the theory are relatively straight forward.
Step One: When 1.0 - 1.5 degree Plato of residual fermentation is anticipated, close the fermenter.
Step Two: Based on the temperature of the beer, let the pressure increase until it is at the appropriate pressure
Step Three: To achieve your desired level of carbonation carbonation, use the C02 pressure chart
Here’s how Spunding works in practice
As fermenters are usually fitted with a pressure relief to release any pressure above 1 bar, this is the limit at the high end of the calculation.
To maintain the pressure at just below 1 bar, you need to adjust the temperature accordingly.
To give an example, to achieve a C02 volume of 2.9, the 1 bar pressure would need to be maintained at 36°F.
Of course, you need to bear in mind the temperature of the fermentation at the time of spunding, as this means the carbonation level will not happen straight away.
You can release or adapt the pressure on a fermenter with a Spunding Valve. The valve releases C02 slowly keeping the tank pressurized.
The spunding valve is used to air in naturally carbonating beer. Keeping your process hygienic and sanitary.
Attach your spunding valve to your tanks late in your fermentation process. You should do this when the yeast has processed most of the sugars in your wort.
There are many benefits to spunding. They have been found to have a brighter flavours and consistent mouthfeel.
Krausening is another process which takes advantage of spunding. Traditionally used by German brewers to naturally add carbonation to beers.
While most commonly used in lagers, because during the lagering stage of the fermentation, the yeast would go dormant, but also used in wheat beers.
Krausening is a method to carbonate beers without the need to use sugars or other adjuncts.
Instead, Krausening works by adding actively fermenting malt wort (around 10% of the volume of the green beer) to the fermented beer. This provides the malted sugars needed for carbonation.
The Benefits of Krausening
As well as being a reliable method of carbonation, there are many other benefits of Krausening. These include:
- Improved flavour: The introduction of fresh yeast clean up the byproducts of lager fermentations, e.g. the diacetyl and acetaldehyde in beer. Granted, these flavours would have been cleaned up during the lagering process, but it’s the addition of fresh yeast, which greatly speeds up the process.
- Increased hop aroma: When adding hopped work, there is an increased hop presence. When you add freshly fermenting and hopped wort to your final beer, these new hop flavours and aromatics are captured in your beer.
- More complete attenuation: Krausening helps high gravity beers attenuate more. When the yeast is dying, add a Krausening solution to a high gravity beer to revive the fermentation and enable the results to be cleaner and dryer.
While there’s a pretty strong case for Krausening, bear in mind that you do need to have a similar beer ready at exactly the right stage in order to do it.
Carbonation is highly important to a beers taste, mouthfeel and presentation. That’s indisputable.
But the method you need depends on your brewery size, the beer’s you are brewing, personal preference, and so on.
There are pros and cons to every technique from forced carbonation with a stone to natural techniques like spunding and krausening.
The key is finding the method that fits in with your brewery and delivers the results you need. Every time.
Have questions? Get in touch.