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Force Carbonation: Tips From the Pros

Dave Colt, Sun King Brewing in Indianapolis, IN

Force carbonating gives the homebrewer a peculiar sense of accomplishment and professionalism. It is a jump that requires new equipment, new skills and faith in your ability to do things right. It is also a heck of a lot faster than bottle-conditioning. You can turn around a force-carbonated beer in 24–48 hours. Compare that duration to one to three weeks for bottle-conditioning.

Rather than filling 50-plus bottles for each 5-gallon (19-L) batch, you can simply fill up one Cornelius keg. And rather than having to clean all those bottles, you just have to clean and sanitize a single container.

If you need to bottle your beer for certain functions where a keg is not a practical container, you can force carbonate in a keg, then counter-pressure fill into your bottles. Basically you will use the “laws of partial pressure” to move pressurized beer from the keg to the bottle — you will need a special tool to get the job done.

This tool is pretty much nothing more than a rubber stopper with a stainless steel tube through the center — there are three different inlets and outlets in the tool. Carbon dioxide flows from one, beer comes out of another, and the last one is for releasing pressure.

Quite simply you put CO2 in, beer in and let the gas out. This process allows you to fill bottles without excess foaming. You need to make sure you bleed off the pressure slowly. The faster you go raises the chances of de-gassing and foaming all over the place.

When you pull the whole thing out, it will cause some foam to rise. This is due to a mini-burst of CO2 and while it is a bit messy, it actually helps to purge oxygen from the bottle. The key is to cap on top of the foam, immediately. If the foam doesn’t come up the neck of the bottle there is a good chance that oxygen is still trapped inside the bottle.

But let me give a word of warning here: there is a significant danger of stressing the bottle if you inject too much carbon dioxide. This could cause the bottle to merely break, shatter or even explode. And again, I return to the fact that it is a time-consuming process to fill bottles. Personally, I would stick with the keg and only counter-pressure fill bottles that you plan to use for beer contests or tasting events.

A Cornelius keg, by contrast, can handle up to 100 PSI. That makes it a lot safer to work with. Aside from the keg, all you really need in terms of equipment is a regulator, carbon dioxide and an extra fitting for the keg that will allow you to push CO2 through the keg’s draw tube. This fitting should be available at your homebrewing store.

The keys to successful carbonation are really simple: temperature and pressure. I would also recommend any literature that provides guidelines for beer styles, including carbonation levels. Carbonation levels are measured in terms of atmospheres of CO2 dissolved into solution. Homebrewers need to rack their beer into Cornelius kegs, then cool the beer to an appropriate cold temperature — the rule of thumb when carbonating is that colder is better (as cold as 28–32 ºF or around 0 ºC). The low temperatures promote CO2 absorption. Once it is cold enough, you are ready to inject the CO2.

The regulator is important here because you set the PSI and push the CO2 down the draw tube. This method allows you to inject the CO2 into the beer, rather than putting the gas on top of the beer. I think you get better results with the carbon dioxide bubbling up through the liquid rather than pushing down through it.

If the regulator is set at 7 PSI and you have a beer temperature of 33 ºF (1 ºC), you can again refer to charts and determine that your atmospheres should be 2.4 in about two days. Since you probably will not have the equipment to make the final measurement of temperature and pressure, you will have to trust the formula from the grids. At least this will bring you close to a proper target. Ultimately, understanding carbonation is as simple as the following equation: atmosphere = pressure + temperature. If you can remember this, the rest is just a question of equipment and proper execution.

Carbonation is really an important component of your final product. Flat beer, after all, is unpleasant to drink (unless a certain style such as a mild or cream ale calls for low carbonation). I think carbonation impacts flavor because it carries bitterness and accelerates the effervescence. Carbonation is critical in bringing out hop characteristics as well — this is especially true with dry-hopped brews. I also think the prickly character of the bubbles adds a degree of  bitterness.