Priming sugar calculator

What brewers ask about the Priming sugar calculator

Why does the temperature the beer finished at matter so much?

Carbon dioxide is more soluble in cold beer. A beer that finished at 12°C is carrying about 1.13 volumes before you add anything; the same beer at 24°C is carrying about 0.81. Prime both the same and the cold one comes out nearly a third of a volume fizzier.

Which temperature do I put in, the whole ferment, or the end?

The warmest the beer reached after fermentation had finished. While it is still fermenting the beer is saturated at whatever temperature it is at; once the gas stops coming off, the CO2 it keeps is set by the highest temperature it saw after that.

How much carbonation should I aim at?

British ales are usually 1.5 to 2.0 volumes, most lagers and pale ales 2.2 to 2.6, and wheat beers 3.0 or more. The default here is 2.2. Going much above 3 volumes in a standard glass bottle is how bottles break.

Does it matter whether I use dextrose or table sugar?

Only in the weight. A gram of table sugar makes slightly more CO2 than a gram of dextrose because sucrose inverts into two hexoses, so you need about 5% less of it by weight. The calculator does that swap for you when you change the selector.

Why do you ask for the pressure over the beer?

Because the residual figure is per bar of CO2 sitting on the beer, and under an airlock that is one bar. If you finished under pressure, spunding at, say, 1.7 bar: the beer is holding correspondingly more, and priming for it as though it were flat would over-carbonate the bottles.