carbonation
Priming
Add a measured quantity of fermentable sugar at packaging so residual yeast generates the intended carbonation in the container.
What is actually happening
The amount is calculated from the target carbonation and the CO₂ already dissolved in the beer, which depends on the temperature the beer has been held at. Warm beer holds less residual CO₂ and needs more priming sugar.
Getting it wrong in one direction gives flat beer; in the other it gives gushers and, with a large enough error or an unfinished fermentation, bottles that fail.
What goes wrong here
Risks rather than certainties. This step does not cause these faults; getting it wrong can.
- Overcarbonation — Too much dissolved CO₂, from over-priming, incomplete fermentation before packaging, or contamination.
- Undercarbonation — Too little dissolved CO₂, leaving the beer flat and dull — carbonation carries aroma as well as providing texture.
- Gushing — Beer that erupts on opening, caused either by refermentation in the package or by fungal proteins from mould-affected barley.
Questions
What makes bottles explode?
Pressure from fermentation continuing in the sealed bottle — because the beer was packaged before fermentation finished, because too much priming sugar was added, because wild yeast is fermenting dextrin the brewing yeast left, or because enzymes from a heavy dry hop are breaking dextrin down. Confirm stable gravity over several days before packaging, measure priming sugar rather than estimating, and store bottles in a crate or sealed box.
Related steps and concepts
- Bottle conditioning — What priming enables.
- Krausening — The alternative using fermenting beer.
Also at the carbonation stage
Bottle conditioning · Force carbonation · Krausening · Nitrogenation
See the whole process in order on how beer is made.
Last reviewed 2026-08-16.