Search: sulfur dioxide

The total gas pressure in beer is measured after the beer has been forcefully shaken. The carbon dioxide is then bound through the addition of potassium hydroxide. The amount of air in the beer contributes the remaining volume of gas. Once the value for the total pressure has been corrected by subtracting the quantity of air present in the beer, the carbon dioxide can be measured [1].

Bound sulfur dioxide in beer is liberated through the addition of acid and subsequent heating. Under a stream of nitrogen gas, the sulfur dioxide is transferred into a receiver containing hydrogen peroxide, and the sulfuric acid thus created is titrated with sodium hydroxide.

SO₂ is primarily present in beer or wine in a bound form (mostly on aldehydes, ketones and sugars). Sulfur dioxide is liberated through the addition of 2 M sulfuric acid and subsequent heating to 95 °C. In an acidic medium, this reaction forms SO₂ ⋅ H₂O from carbonyl sulfite adducts, which can no longer act as a functional nucleophile. Additional heating reduces the solubility of gases, causing SO₂ to diffuse through a Teflon membrane where it is dialyzed in a 1% sulfuric acid solution. It then reacts with formaldehyde to form a carbonyl sulfite adduct (HO-CH₂-SO₃H). This adduct binds at a temperature of 45 °C to para-rosaniline forming a red complex; the absorbance is measured at 560 nm with a UV-VIS detector. When performing the analysis, care should be taken to only use the Teflon membranes listed below; otherwise, other Maillard reaction products can cause incorrect blank values.

In addition to other ions, sulfite can be determined using an ion exchanger with ion chromatography.

Through the addition of a sodium hydroxide solution, the carbon dioxide in beer becomes bound as sodium hydrogen carbonate or sodium carbonate. Sulfuric acid is added to an aliquot of the beer treated with sodium hydroxide. This causes the carbon dioxide to be released again, after which a stream of air conducts the carbon dioxide into a barium hydroxide solution. Through titration of the excess barium hydroxide, the carbon dioxide content of the beer can be determined [1].

The thermal conductivity is measured in a small chamber, which is in turn separated using a semi-permeable membrane from the medium being measured. The diffusion through the membrane alters the thermal conductivity in the measurement chamber. The gas volume in the measurement chamber is completely replaced in 10–20 s cycles. The changes in the thermal conductivity over time are a function of the quantity of CO₂ diffusing across the membrane. Using this value and taking into account the temperature, the concentration in the medium being measured can be calculated. Other dissolved gases, such as nitrogen and oxygen, do not affect the result of the measurement, since either nitrogen or air is used to replace the gas in the measurement chamber [1].