Carbonating bottled beer can be as much an art form as brewing beer. Everyone has their own, preferred technique based on quality, time and equipment. For some, naturally carbonating is the best way to go. Others prefer force carbonating. Any carbonating method can produce flat or over-carbonated beer. The key is making careful measurements to avoid problems with the finished product.
Most beginners start by naturally carbonating their beer. This method simply works. No additional equipment is needed for carbonation. All the home brewer needs to do is add a measured amount of carbonation sugar before bottling. Brewing companies supply carbonation sugar by the pound, in ready measured bags and priming tablets. Typically brewers use 3/4 cup of corn or table sugar per five gallons of beer. Priming tablets work in much the same way, but the tablet goes directly in the beer bottle. A 12 ounce beer bottle takes one tablet. A 22 ounce bottle uses two per bottle. More is never better when it comes to priming sugar. Too much priming sugar can cause bottles to explode. The beer is bottled, capped and allowed to sit at fermentation temperature, which is around 70 degrees Fahrenheit, for two or three weeks.
Beer carbonated this way is not completely clean. Bottles typically have a small amount of sediment at the bottom and drinkers have to be careful to avoid stirring it up or drinking all the way to the bottom. One solution is to partially filter the beer to remove excess yeast. It only takes 10% of the total suspended yeast in a batch of beer to carbonate. This means home brewers can set aside 10% of the finished beer after racking and filter the rest. This will not prevent all of the sediment in the finished product, but it might prevent some of it.
Force carbonation is an alternate method. Many brewers find it easier to force carbonate kegs rather than bottles. Systems that can force carbonate bottles are more expensive. The principle for both systems involves attaching a CO2 cylinder to a sealed container by means of a hose and a regulator. The amount of pressure used depends on the temperature and amount of carbonation desired. Typically brewers will test the temperature of the refrigerator where the beer will be kept during the carbonation process, then check the CO2 parts per volume on a chart which gives the needed CO2 pressure for the regulator. Do not attempt to to pump more than 5 PSI above the target pressure. It may be necessary to shake the keg during this process to help the CO2 bubbles mix into the liquid. As this happens, the pressure from the regulator will drop. Increase it until it reaches the desired pressure again, but watch closely to ensure that the pressure does not reach unsafe levels.
Depending on the specific gravity of the beer, the force carbonating process can take anywhere from three or four days to a week or more. When the beer has enough dissolved CO2, simply remove the valve, hose and regulator and seal the container.
Natural and forced carbonation both have their merits. When brewers use natural carbonation, the end product is typically smoother, but the flavor can be more yeasty. Fruity yeasts come through well with natural carbonation. Forced carbonation typically has a crisp, clean flavor and a lighter head of foam. Bottling is much easier for craft brewers who use natural carbonation while keg brewers find that carbonation times are better when using forced carbonation. Both require careful measurement to ensure the the right level of carbonation.