Browsing by Author "Tenhovirta, Santeri"

In the thesis, the effects of six different lactic acid bacteria (LAB) species on properties of sour beer was studied. As the fermentation by LAB may yield unexpected results, and as the prediction of specific organoleptic compounds present in LAB-fermented sour beers has proven to be challenging, sensory and chemical properties of sour beers fermented with selected LAB was assessed. The main research question was “are there statistically significant differences between the different sensory properties of the sour beers produced with different LAB species?”. Use of Lactobacillus plantarum, L. rhamnosus, L. brevis, L. buchneri, L. delbrueckii and previ-ously unreported in sour beer brewing, L. alimentarius, was assessed. Fermentation was carried over approximately six weeks, during which the changes in viable cell density, pH, refractive index, organic acid and ethanol (using PDA/RI) and sugar compositions (using HPAEC-PAD) were assessed. Sensory evaluation was performed in two parts: Overall preference rank test with untrained panellists and descriptive analysis with trained panellists. Differences were found in the results of viable cell count, organic acid composition and descriptive sensory analysis. Increase in lactic, acetic and succinic acid and ethanol over the fermentation period was detected. Decrease in citric acid, maltose, glucose and sucrose was detected. Novel L. alimentarius yielded fastest growth rate, with encouraging results from sensory analysis. L. delbrueckii did not grow in the substrate media, allowing possible infection to take place. L. brevis and L. buchneri yielded acetic acid concentrations detectable in sensory and chemical analysis. Increased lactic acid concentration was associated with increased overall rank, raspberry aroma and apple and vinous flavours, with negative correlation to butyric, rancid and yeasty flavours and bitter aftertaste. Further studies are suggested to assess the effects of fermentation temperature, O2 availability, wort composition and buffering capacity on the results of the LAB fermentations.