Focusing on efficiency and environmental impact, I'd say minimizing carbon dioxide usage would be optimal. In-tank, this would basically mean the low-and-slow method (i.e. apply the minimum pressure required and rely on extended time to reach equillibrium/saturation). From my experience this usually also results in the best-quality outcome, though compromises are very often made to speed carbonation in order to meet production/scheduling needs.
"What is the proper pressure to apply?"
Start with the minimum amount:
- Find the required pressure to achieve the desired carbonation at a given temperature (from a carbonation chart). This is usually 8-12 psig, and is also where you want to keep the tank's head pressure set.
- Add the static pressure, exerted by the height of liquid above the carbonation stone. Every 28 inches of liquid height will add ~1 psig of static pressure. This ranges from negligible in small tanks to quite critical in larger (especially taller) tanks.
- Add the resistance pressure (a.k.a. the wetting pressure, basically what's required to force gas through the tiny pores) of the stone. Usually 3-10 psig. Find this by submerging the fully assembled stone in water (while rebuilding a tank after a full breakdown, say), then starting at 0 psi, slowly increase the supply pressure just until you see bubbles coming through the stone.
- Of course don't forget to take account for your local atmospheric pressure, based on altitude.
Any additional pressure will speed up carbonation (to a point) but risks over-carbonation, stripping of aromatics and/or foaming. A flow indicator (see below) helps to assure there actually is gas flow, useful since there's always some imprecision in these calculations (not to mention in pressure gauges and regulators).
"Is there an optimal flow? (in L/min for example)"
This depends on carb stone size and quality, volume of beer, vessel geometry, temperature, etc. I always use a rotameter inline to indicate and/or adjust gas flow-rate, but keep in mind these tend to be calibratred to air at standard temperature and pressure, so you'll have to correct for that (pure CO2 at whatever your supply pressure is). For large tanks (180+bbl) I would cap the flow at ~3 cubic feet/minute at a supply pressure of about 45 psi. For small tanks (>15bbl) I wouldn't go much beyond 0.5 CFM at, say, 15-20 psi. It's all about finding the right rate for your particular setup so CO2 goes into solution rather than just bubbling through and needing to be bled off. These numbers were established empiracally.
"What do you do when the tank starts to bleed from the PRV but still not at desired CO2 level?"
Ideally (again, considering efficiency and environmental impact, not to mention quality), you'd want to avoid this entirely, since any gas coming out the top is just "waste" that didn't dissolve, and may be carrying with it desirable aromatics. When it "needs" to happen, simply try to minimize it by adjusting other factors (gas flow rate, supply pressure, beer temperature). In practice, it's a very common compromise to speed up the process. I'd always try to avoid this method at all costs for highly aromatic beers (anything hoppy really, every bit counts). You'd really just have to see what impact it might have on quality in your particular case, though.
"Is there a temperature above which you are loosing your time and CO2?"
Yes, though again it depends on your particular needs. I'd generally never apply carbonation unless the tank is below 40 deg. F (and then only in extenuating circumstances), as it's roughly the max temp where you can reach common carbonation levels (~2.5 vol.) without exceeding 14.7 psi (1 bar) in the tank. Better that the beer is closer to or just below 32 deg F. Warmer beer will be more prone to loss of aromatics by stripping.
If you search "carbonation" on the MBAA community site, you'll come up with some good information, too:
I'm a big proponent of practicing cautious and informed experimentation when establishing procedures like this, so just keep in mind the what the most important factors to you are (such as efficiency, environment and quality) and see how small changes in procedure affect each of them. Also, practicing some type of natural carbonation could be a great way to really maximize your goals of efficiency and environmental consideration. I hope this helps, or at least gives you a jumping-off point.
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Zandy Zeiser
Brewer-at-large
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Original Message:
Sent: 11-10-2023 08:30
From: Dominic Charbonneau
Subject: Force carb good practice
Hi, I was wondering what is the most optimal carbonation procedure efficiency wise and environmentally wise. I've seen many ways to carb a beer in a bright tank with a carb stone and had good discussion about it therefore wondering which is the best one.
- What is the proper pressure to apply?
- Is there an optimal flow? (in L/min for example)
- What do you do when the tank starts to bleed from the PRV but still not at desired CO2 level?
- Is there a temperature above which you are loosing your time and CO2?
I know that probably the best is to carb in line, but most of breweries around the world do not have this equipment.
DOMINIC CHARBONNEAU
VP PRODUCTION & BRASSEUR EN CHEF
B 450 250-2611, POSTE 223
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