Saturday 16 July 2022

Will My Beer Be Carbonated After Pressure Fermenting?

This is a question posed by many brewers who are new to pressure fermentation. The answer is "yes", but exactly how much carbonation is in your beer at the end of fermentation will depend on a couple of things though - namely what temperature you fermented at and how much pressure was applied/captured during fermentation.

The amount of carbon dioxide (CO2) that is absorbed into your beer is measured in volumes of CO2. The number of volumes of CO2 that can be absorbed into your beer is dependent on what temperature your beer is at. The colder the beer, the more easily CO2 is absorbed for the purpose of carbonation.

You can use a carbonation chart like the one below to calculate how much pressure is required to reach your desired carbonation level (click the image to make it bigger and easier to read).

Keg King Carbonation Chart

As an example, if you fermented a pale ale at 20 degrees Celsius and wanted to achieve 2.4 volumes of CO2 for carbonation, you would need around 28.4psi of pressure in the fermenter to achieve this. This is a reasonable amount of pressure and towards the upper end (though still within the limits) of what some pressure capable fermenters are able to safely hold which is around 35psi.

20 degrees Celsius and 2.4 volumes requires 28.4psi

This is certainly achievable using the CO2 that is generated by fermentation by setting the spunding valve on your pressure fermenter accordingly.

Keep in mind though that pressure fermenting is believed to cause additional stress on yeast. The generally recommended limit for pressure fermenting is 15psi however there's still plenty of study and research being undertaken to fully understand the impacts of pressure fermentation. Pressure will affect different yeast strains differently too. Also remember that CO2 gas is not absorbed into beer instantly - it takes time, and will be absorbed faster at colder temperatures.

An alternative option, which is the method we use, is to ferment at 10-15psi which will achieve partial carbonation in the beer. Once fermentation is finished top the fermenter up to around 20psi of pressure, disconnect the gas source and then initiate a cold crash. During the rapid temperature drop of the beer during a cold crash, some of the 20psi of pressure in the headspace is absorbed into the beer - as CO2 is more easily absorbed at colder temperatures. Using this method we get pretty close to full carbonation by the time our cold crash is completed.

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