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Master Brewers Association of the Americas > BREWING RESOURCES > Ask the Brewmaster > Posts > Batch Carbonation
July 28
Batch Carbonation

​Q: Dear Brewmaster, 

I work at a brewery on a Caribbean Island, we are having problems with dialing in our CO2 levels in the bright beer tanks. We usually end up with about 100-95HL in our bright beer tank. Coming out of our fermenter our beers usually have 3.5-4.5 grams per liter of CO2. We filter one day then package the next (about a 12-16 hours between end of filtration and beginning of packaging). We generally leave our beers under 1-2 bars of pressure depending on the volume in the tank and time until packaging. On the day of packaging, if our CO2 levels are low we pump more CO2 in from the bottom of the tank. If we are high, we have to release all the pressure from the tank and purge CO2 out of the beer then re-pressurize the tank. (This is very costly for us, and a waste of CO2).

Are there any formulas we can be using that factor in Time, Temp., volume and initial CO2 levels to help us hit our carbonation range in bright beer tank?

Thank you for your insight!

A: Typically, these questions are answered electronically; however, due to your location I think we should consider a site visit to fully assess your situation. 

It sounds like your filtered beer has fairly typical CO2 levels (~1.8-2.3 volumes) compared to what I've seen in the average US microbrewery. You didn't mention your target CO2 spec for packaging, but it's got to be at least a bit higher than the upper end of the range you gave for your filtered beer. Unless your carbonation stone is undersized (or soiled) or cooling is inadequate, hitting your packaging spec in 12-16 hours, without wasting CO2 during the process should be no problem.

First, it's critical to understand that the volume of CO2 dissolved in your beer at any given moment is always equibilrating toward a theoretical value determined by the conditions (temperature and pressure) at that moment. For example, if you were able to maintain 12psi of CO2 head pressure and 35F in your BBT, you'd eventually end up with the 2.73 volumes listed on the charts that come with CO2 volume meters. This would be true regardless of the starting carbonation value; however, it might take days or even weeks to reach 2.73 volumes, depending on your starting value. Since none of us have that kind of time, we use carbonation stones and attempt to optimize temperature and pressure to hit carbonation specs faster. Take note from the chart that, given enough time, beer left under 1-2 bar at cold temperatures will become substantially over-carbonated.

As soon as filtration is complete, record all of the usual suspects: volumes of CO2, beer temp, bbl/hl of beer, tank head pressure, DO, and verify cooling is on the BBT. I'll assume your BBT head pressure at the end of filtration is ~1 bar. If it's low, plug the current temperature and CO2 volumes into your chart to solve for pressure. You'll want to immediately top up head pressure to at least this value to prevent degassing (ie if you have 36F beer and 2.20 volumes CO2, get the head pressure to at least ~7psi). If you will be intentionally venting the tank (to scrub DO) at the beginning of carbonation, be sure head pressure never falls below this point.

To get flow through a carbonation stone, you'll need to set the regulator pressure higher than your desired equilibrium pressure on the chart because you have to overcome hydrostatic pressure (depends on the height of the column of beer in your BBT) and capilary pressure of your porous carbonation stone (depends on the stone, but usually ~5psi). Avoid the temptation to just set the pressure high and let it rip. CO2 injection must be slow to create small bubbles that are readily dissolved. If you go fast, many of the large bubbles created won't dissolve. This results in foaming (which damages foam positive proteins), unnecessary scrubbing (loss of hop aroma/desired volatiles), and a huge waste of CO2. There are 2 common approaches to limiting CO2 flow at higher regulator pressure settings: either step up regulator pressure in small increments over several hours or install a needle valve of some kind (better). Some brewers also use an adjustable PRV on the blow off arm of the BBT so they can set it to blow off at a desired equilibrium pressure. This helps to prevent both over-carbonation (by limiting the max head pressure) and degassing (by limiting venting/the min head pressure). Blow off valves simply left cracked open for venting can cause the head pressure to fall too low - which results in degassing instead of carbonation. Our friends at the Brewers Association put together a very good lecture about carbonation a while back - you might want to check that out for some additional information.
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