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Why is my Beer Over-carbonated?

Carbonation is carbon dioxide (a yeast byproduct of fermentation) being held in solution. It makes our beer bubbly, and carbonating one way or another is a necessary step in creating finished beer. Sometimes, however, things don’t go quite right and your beer becomes over-carbonated. Here we’ll go over some of the possible issues that caused either a single bottle to be over carbonated, or an entire batch.

Understanding Bottle Conditioning

Homebrewers who bottle rely on a secondary fermentation inside of the bottle to carbonate a beer. To do this we add a certain volume of sugar depending on the desired level of carbonation we want. Different styles of beer call for different levels of carbonation. For example the lowest end of the BJCP range is 1.5 volumes of CO2 (English Bitter), all the way up into the lower threes in volumes of CO2 for styles like belgian dubbels, tripels, and blonde ales. Dunkels also have a relatively high volume of CO2 for to style carbonation. A great (and easy) way to calculate the amount of sugar you need, is to use one of the many online “priming sugar calculators”. They will ask you a few questions:

  • Style of Beer or Volumes of CO2 desired: Each calculator lists a slightly different amount of CO2 needed for the style, but they do give a list of the style and the volume of CO2 needed.
  • Temperature of Beer in Fahrenheit: This is the current temperature of the beer, or the highest temperature the beer reached post fermentation, whichever is higher. This tells the calculator how much CO2 dissolved out of the beer post fermentation.
  • Volume of beer to be bottled: This is the amount of beer you’re bottling.

The calculator will then give you a weight or volume of sugar to use for your batch. Personal preference and the style of beer help make the decision of how much carbonation we want. Now let’s look at what can go wrong to cause over carbonation in bottles.

So why is the beer over-carbonated?

Too Much Sugar

Over-carbonated beer[/caption]The most common way to prime (add sugar before bottling for carbonation) beer for bottles is to dissolve the sugar in some water and rack the beer on top of it. This helps distribute the sugar evenly as the beer is racked to a bottling bucket. Since you don’t want to be stirring the sugar solution into the beer (to prevent unnecessary oxidation), the sugar is more concentrated in one area of the beer than another. While uncommon, this if often the reason for one bottle being carbonated significantly more than the rest in that batch. If the entire batch is more carbonated than you like, it is a matter of using less sugar the next time. To help prevent uneven distribution, I don’t recommend stirring the sugar solution in. If you are racking into a bottling bucket, add your priming solution in first. Then as you rack, have the beer flow on the side of the bucket (below the surface of the beer to avoid splashing). This can help create a gentle spiral motion and help evenly distribute the sugar solution into your beer. If you are bottling directly from primary, add the sugar solution 24 hours before bottling. This gives the sugar solution time to distribute evenly. If you are concerned about priming the entire batch at once unevenly, you can take the weight / volume of sugar given to you by the calculator, and then divide it by the number of bottles you have. Then you’ll add that to each bottle individually before filling it. There are roughly 10.66 bottles of beer per gallon, but rounding down to 10 per gallon accounts for any trub in the bottling vessel.


Both professional and home brewers alike take great care in sanitizing their equipment to prevent infection. Infections can cause off flavors and easily cause over-carbonated beer. Certain bacteria (brettanomyces in particular), can ferment more complex sugars that standard beer and wine yeast can not. They also tend to work slower, making it hard to spot an infection pop up in a typical beer turnaround time of 2-3 weeks. You’ll prime and bottle your beer, but in the meantime, bacteria could be working on those extra sugars that got left behind. This creates an excess of CO2 trapped in the bottle. When you go to open it, a gush of foamy beer comes flying out. In some cases the infection can ferment enough residual sugar to create a “bottle bomb”. These occur when there is more pressure inside than the bottle can handle. Bottle bombs are very dangerous, especially if the bottle fails in the vicinity of people, as glass will shoot out in all directions. There is enough pressure to shoot parts of the bottle into the ceiling. The best way to avoid bottle bombs is proper sanitation, and ensuring the fermentation is complete before bottling.

Other Factors

Sometimes, you have the perfect amount of carbonation, but your beer isn’t cold enough. Cold beer absorbs CO2 that would be left in the headspace of a warmer bottle conditioned beer. If your beer is flatter than you expected, try cooling the next few bottle in the fridge for a longer period of time. Another sign of this is a big head that fades quickly and leaves little carbonation behind in the beer as you drink it. If you store your bottles on their side for even a day or two, the sediment that would have been on the bottom of the bottle is instead now on the side. I’ve found that opening one of these up can cause a gusher (despite having the proper amount of carbonation) as the sediment is in a larger surface area. The larger surface area creates more nucleation points for CO2 in solution to latch onto and escape. This is the same reaction as the diet coke and mentos videos. Now that you have a better handle on how bottle carbonation works, you’ll be able to interpret the different issues that can cause over carbonation, and correct them for next time.