Priming sugar

Priming sugar is a precise dose of fermentable sugar, most often corn sugar, table sugar, or dried malt extract, dissolved and mixed into beer right before it goes into bottles. The yeast still present in the beer consumes this small addition and produces carbon dioxide, and because the bottle is sealed, that gas has nowhere to go except into solution, carbonating the beer naturally over one to two weeks at room temperature.

The amount used depends on the beer's volume, its temperature during fermentation, and the carbonation level you want for the style, since a crisp lager and a soft cask ale call for noticeably different CO2 levels. Priming calculators account for these variables and are the standard way brewers land on an accurate dose rather than guessing.

Getting the amount wrong is the most common problem: too little sugar leaves beer flat, and too much can overcarbonate it or, in more extreme cases, build enough pressure to be a genuine safety concern with glass bottles. Uneven mixing is another frequent issue, where sugar concentrates in some bottles and not others if it is not stirred evenly into the whole batch before bottling, leading to inconsistent carbonation bottle to bottle.