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Query about CO2 saturation in fermentation and secondary tanks


Aug 1, 2021
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referring to industrially brewery conditioned beer in secondary tanks that is force carbonated (and NOT krausened or primed while in the secondary tanks)

01) Is the secondary (conditioning) tank ALWAYS pressurized even if the beer will be force carbonated in BBTs later after filtration/centrifuging? If not pressurized i assume CO2 saturation continues or it is already fully saturated from the primary fermentation?
Does pressurized mean merely sealing the tanks air-tight or the actual application of external pressure on the contents of the tank.
[I am use the term 'saturation' as the CO2 that is absorbed into the beer WITHOUT any externally applied pressure].

02) What volume of CO2 would get saturated in the beer (without pressurizing) during the fermentation and then further in the secondary? I do understand that cooler the temperature more the CO2 will dissolve)

03) In the case of nitrogenated beers they say it is like 70/30 N2/CO2 . Does this mean they spund/stone with a CO2 and N2 mixture or is it that CO2 is already saturated in the beer during primary and secondary to around 30% and pre N2 is dissolved as the remaining 70% component

04) Once pressure is applied to dissolve CO2 does t mean that all further/future processes and operations must be done isobarrically ?

05) In general, is the conditioning temperature of lager style beers lower than their fermenting temperatures or the same? What about ales?

Thank you

These answers are required for theoretical purpose of teaching conditioning and beyond which i understand have several regimes and are quite personalized to each brewery


Grandmaster Brewer
Sep 6, 2011
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Ventura, CA
CO2 solubility is always going to follow Henry's Law, which means temperature and head pressure influence the gas in suspension. Primary fermentation without some venting will result in not only unsafe tank pressures but also an unworkably over carbonated product. Luckily, there's a few assumptions and charts we can consult to predict the carbonation result.

1) No. Primary fermentation is always vented between atmosphere up to about 15psi. Pressurized fermentation is practiced at many breweries, but not a majority. Yeast activity is adversely effected by high carbonation levels, so saturation is usually below final carbonation levels. Remember that tank size and shape is also relevant because of the static head pressure from the sheer volume. Many strains of yeast will not perform well under pressurized conditions. What is typical is for a QA "forced fermentation" sample to be created where the attenuation can be measured well before the actual product achieves it. Since yeast releases an equal number of CO2 molecules to alcohol, the brewer can then decide when to close off the vessel to achieve natural carbonation based on how many g/L are remaining. Generally this becomes shorthand of about 1.5 to 2 plato remaining to full attenuation.

As an aside, filtering and centrifuge operations can be performed under pressure so that minimal CO2 is lost. However the process can be difficult and lossy, so many breweries elect to process with flat or low carbonated product and polish off in the bright tank.

2) Again, Henry's Law tells us that gasses will be dissolved in equilibrium with the head pressure. At atmosphere, the CO2 will be approximately 1 volume, depending on residual sugar and alcohol content since those factors have a slight influence solubility.

3) Typically 1 volume of CO2 is in the beer and nitrogen is added to the beer in the brite tank.

4) In theoretical terms, yes. In all practicality, some gas loss is expected in packaging. This is highly variable between kegs, bottles and cans. It's been my experience that carbonation is achieved at 34*F (1.1c) and then temperature is lowered to 32*F (0c) or below to minimize CO2 loss. This is especially relevant to bottling and canning where some foam is needed to fill the top space before capping and reduce O2 ingress. Too much foam = low fills, too little = high fills. Either way its an unacceptable loss of sellable beer.

5) Ales an lagers typically condition at the same temperatures to assure uniform carbonation.