Revision as of 20:49, 1 April 2008

Accurately calculating the carbonation is a great exercise for working with apparent and actual attenuations as well as working with the extract % or Plato scale. The latter is not essential, but makes things more intuitive.

The final carbonation of bottle conditioned beer depends on the CO₂ currently present in the beer and the CO₂ that will be generated during bottle conditioning.

The amount of CO₂ already in the beer depends on the CO₂ pressure and the temperature of the beer. It can be determined by using a Carbonation Table. These tables show the equilibrium of CO₂ content that exists for a given CO₂ pressure and beer temperature.

The amount of CO>sub>2</sub> created by bottle conditioning is based on the amount of sugar that is fermented. Each gram of fermentable extract is fermented into equal parts (by weight) of alcohol and CO₂ (this is not exactly true, but close enough for this calculation).

corn sugar

The easiest way to add fermentable extract to beer is through the addition of pure sugar. This can be dextrose (corn sugar) or succrose (table sugar). Most corn sugar is actually glucose monohydrate. This means that each glucose molecule bound with a water molecule which adds to its weight but not to the potential of CO₂ that can be produced [BYO]. Glucose monohydrate contains 9% water by weight, which means that only 91% of its weight can be considered for the CO₂ calculation.

The formula for calculating the carbonation when priming with corn sugar is:

C_beer = C_flat-beer + 0.5 * 0.91 * m_corn-sugar / V_beer

• C_beer - the final carbonation of the beer (g/l)
• C_flat-beer - the CO₂ content of the beer before bottling (g/l)
• m_corn-sugar - the weight of the corn sugar (glucose monohydrate) (g)
• V_beer - beer volume (l)

table sugar

Table sugar, succrose, does not contain any water and yeast will convert half of its weight to CO₂

C_beer = C_flat-beer + 0.5 * m_table-sugar / V_beer

• m_table-sugar - the weight of the table sugar (succrose) (g)

dried malt extract

When using malt extract for priming, its fermentability needs to be taken into account. A typical aparent fermentablility (limit of attenuation) of malt extract is 80%. (a 12 Plato wort will finish at 2.4 Plato / 1.048 OG - 1.010 FG). But to determine the true fermentability the true fermentability needs to be calculated. To convert between apparent and true attenuation, the following formula can be used

A_true = A_apparent * 0.88

• A_true - true attenuation
• A_apparent - apparent attenuation

Speise

sources

• [BYO] - BYO - Priming with Sugar