Hydrogen sulphide in brewing.

Nagami, K., Takahashi, T., Nakatani, K. and Kumada, J.

Abstract
In view of the shortening of fermentation and maturation times in current brewing, it is important that the H₂S level in beers is reduced below the taste threshold level before these processes are completed, otherwise an immature flavour will be produced. To follow the behaviour of H₂S during fermentation and maturation, modifications were made to a method of determining this substance developed earlier. In the modified method a headspace sampling system was used linked to a gas chromatograph with flame ionisation detector. Methyl ethyl sulphide was employed as internal standard and quantitative measurements were obtained from peak lengths on the chromatogram charts. Only a very short period (20 to 30 min) is required for analysis which covers the range 0.1 to 300 ppb with an accuracy of below 10% of standard error. Variations in H₂S content in both pilot plant and brewery fermentations were followed using this method. Several peaks of H₂S production were found during the fermentations. The first peak appeared just before initial yeast growth, the second and third at around 20 and 40 million cells/ml of yeast concentration respectively and the fourth occurred at maximum yeast concentration. Hence it is concluded that H₂S production is closely related to yeast growth. Temperature, carbon dioxide pressure, wort aeration and 'trub' content did not fundamentally alter the relationship between H₂S production and yeast growth but did affect the concentrations of H₂S produced and their subsequent removal. The absorption of oxygen by green beer at racking has a considerable effect on the concentration of H₂S during maturation and efforts should be taken to avoid O2 uptake whenever possible.
Keywords: analysis brewing carbon dioxide fermentation hydrogen sulphide maturation oxygen sulphur compound trub