/ WORT, BEER AND BEER-BASED BEVERAGES / Beer / Carbon Dioxide

B-420.26.009 [2020-10] Carbon Dioxide, Stadler and Zeller – Manometric Method

The quantity of dissolved carbon dioxide is an important quality attribute of beer. A satisfactory level of carbonation (bottom-fermented beer 0.40–0.60 % w/w, top-fermented beer 0.40–0.80 % w/w) contributes significantly to the perceived freshness and drinkability of beer.

Beers containing little carbon dioxide taste flat. Additionally, the carbon dioxide in beer promotes the formation of foam. The flavor thresholds of the flavor and aroma components in beer are altered by the quantity of carbon dioxide in solution.

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This method is based on the Henry-Dalton law, according to which at a given temperature, the concentration of an ideal gas dissolved in a liquid is proportional to the partial pressure of the gas in the gas phase, given that equilibrium exists. This steady state is reached by forcefully shaking the beer. A manometer is used to measure the total pressure.

Aside from carbon dioxide, there is always a certain amount of air present in the neck of bottled beer as well, causing the partial pressure of the carbon dioxide to shift. Therefore, in order to obtain accurate results, besides the total pressure, the “quantity of air” in the beer must be measured, i.e., the values measured for carbon dioxide, due to the analysis principle, are always too high. For precise measurements of the CO₂ content, the partial pressures of the foreign gases (e.g., O₂, N₂) must be taken into consideration.

The result is determined according to the so-called Haffmans equation:

\(CO_2 \space \text{in % w/w} = (p \space + \space 1.013) \space \times \space e^{\left(-10.73797 \space + \space {2617.25 \over T \space + \space 273.15}\right)}\)

p	= overpressure in bar (CO₂partial pressure)
T	= temperature in °C
1.013	= atmospheric pressure in bar

\(CO_2 \space \text{in % w/w} = P \space \times \space e^{\left(-10.73797 \space + \space {2617.25 \over T \space + \space 273.15}\right)}\)

P	= absolute pressure in bar (CO₂ partial pressure)
T	= temperature in °C

For p = overpressure in bar and P = absolute pressure in bar, insert the partial pressure of CO₂.

The Haffmans CO₂ equation is based on the solubility of CO₂ in beer with an original gravity of 12 % w/w and an apparent attenuation of 80 %.

The solubility of CO₂ in beer changes 1 % for every 3 % (w/w) original gravity.

The Haffmans equation is used independent of the alcohol content of the beverage, given that the constants (-10,73797 und 2617,25) are already present in it.

For carbonated beverages with a sugar content of more that 10 g/l, the reduced solubility of CO₂ due to the dissolved sugar must be taken into account. For this reason, for every 30 g/l of sugar subtract 0.098 bar from the measured pressure.

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non-alcoholic beverages

Application/Purpose

Determination of dissolved carbon dioxide concentration in carbonated beverages in bottles and cans by means of pressure and temperature measurement

Scope of Application

Suitable for determining the concentration of dissolved carbon dioxide in carbonated beverages to which N₂ has not been added. The concentration of dissolved oxygen (> 0.5 mg/l) in the beverage must be taken into account in the calculation.

Principle

The carbon dioxide concentration is calculated from the pressure and temperature after piercing the container and shaking it vigorously [1, 2].

Since the air present in the container is not taken into account, the results are somewhat too high. In the case of beer, however, the influence of the headspace gas can be reduced by measurements immediately after bottling by means of so-called snifting (see procedure). The advantage of this method is that it can be carried out very quickly.

For precise measurements, the partial pressures of the dissolved foreign gases (O₂, N₂) must be taken into account if necessary.
For carbonated beverages with a sugar content of more than 10 g/l, the lower solubility of the carbonic acid due to the dissolved sugar must be taken into account.