Effects of fermentation temperature on the composition of beer volatile compounds, organoleptic quality and spent yeast density

Ademola O. Olaniran*¹ · Yushir R. Maharaj¹ · Balakrishna Pillay¹

¹Discipline of Microbiology, School of Biochemistry, Genetics and Microbiology, Faculty of Science and Agriculture, University of KwaZulu-Natal, Republic of South Africa

*Corresponding author: olanirana@ukzn.ac.za

Financial support: This study was supported by the South African Breweries and Competitive Research Grant of the University of KwaZulu-Natal, Durban, South Africa.

Keywords: beer volatile compounds, fermentation temperature, organoleptic quality, spent yeast density.

Production of good quality beer is dependent largely on the fermentation temperature and yeast strains employed during the brewing process, among others. In this study, effects of fermentation temperatures and yeast strain type on beer quality and spent yeast density produced after wort fermentation by two commercial yeast strains were investigated. Beer samples were assessed for colour, clarity and foam head stability using standard methods, whilst the compositions and concentration of Beer Volatile Compounds (BVCs) produced were assessed using GC-MS. The spent yeast density, measured as dry cell weight, ranged between 1.84 - 3.157 mg/ml for both yeast strains with the highest yield obtained at room temperature fermentation. A peak viable population of 2.56 x 10⁷ cfu/ml was obtained for strain A, also during fermentation at room temperature. The foam head of the beers produced at 22.5ºC was most stable, with foam head ratings of 2.66 and 2.50 for yeast strain A and B, respectively. However, there was no significant (p = 0.242) difference in colour intensity between the beers produced at the different fermentation temperatures. Eight different BVCs were detected in all beer samples and were found to affect the organoleptic properties of the beer produced. Further optimizations are required to determine the effects of other parameters on beer quality.