Principle component analysis

The Headspace GC-MS results from Exp 1 and 2 was evaluated with Principal Component Analysis (PCA). To eliminate higher contribution from high abundant compounds was the 4th. root of the ppm values used in the PCA calculations.

Figures 24 and 25 show the scores plot with two different labelings: Figure 24 with coloring yeast / Kveik strains while Figure 25 coloring on fermentation tem-perature. Figure 26 shows the loadings plot. The overall impression is that PC1 separates on yeast strain while PC2 partly separates on temperature. Some of the Kveik strains are close to the commercial yeast strain WLP001 while Muri and Hornindal are closer to the Idun bakers yeast strain. Sigmund and Stranda strains seem to most distant from any of the two reference strains. And not surprisingly, it is the esters (active amyl acetate, isoamyl acetate, isobutanol acetate and ethyl acetate) that are produced at higher concentration at 30^◦C that contributes most to separation between the fermentation temperatures (negative values on PC2 axis in loadings plot Figure 26).

Figure 24: PCA of volatile compounds according to Kveik / yeast strains

Figure 25: PCA of volatile compounds according to fermentation temperature

if the beer fermented with Kveik and Idun at 19 ^◦C could be distinguished from WLP001 fermented beer used as a reference. 17 assessors participated in the study and were asked to taste two samples, to identify which one was equal to the ref-erence. The assessors where asked to subjectively rate the beer which was not be equal the reference on a scale from 1-5. The number of correct responses and taste rating for each yeast is given in Table 9.

Table 9: Number of correct responses to determine if there is a significant differ-ence in taste when comparing beer brewed with a referdiffer-ence yeast (WLP001) and Norwegian Kveik and Idun and a subjective rating

Number of

17 Assessor participated, in order to determine if there is a difference, 13 correct responses are required to conclude that a perceptible difference exists at 95 % confidence interval. From Table 9, there is a significant difference in taste between WLP001 and Muri, Stranda and Idun. Using Equation 4 (Appendix C), it can be concluded with 95 % confidence that at least 34 % of the population can recognize beer brewed with Muri yeast, 70 % can recognize Stranda, and 100 % can recognize Idun. 5 % of the population can recognize Sigmund and Hornindal.

The assessors were asked to rate the beer they determined to be different from the reference to either be equal, better or worse. Idun, Muri and Hornindal were rated better then WLP001. Sigmund and Stranda were rated to taste worse.

Too investigate the effect of yeast a heat map was generated. The concentration of

compounds for WLP001 from experiment 1 are given in Table 21 - 26 in Appendix A.1 were divided by the concentration of Muri, Stranda, Hornindal, Sigmund and Idun from Table 21 - 26 in Appendix A.1 and the log₂ of the division was used to calculate the relative difference in concentration. The heat map was generated using conditional formatting. The heat map is given in Figure 27.

a No peak was identified at the specific retention time, giving no detection of the compound

Figure 27: Heat map representing color coded concentration differences of yeast com-pared to WLP001. Three-point color scale, negative values (red color) represent a higher concentration of the given compound for the Kveik and Idun, positive values (green color) represent a higher concentration of the given compound for WLP001. The midpoint value was defined as 0 (white color), representing no changes in concentration.

Idun was the highest rated beer (3.5), followed by Hornindal and Muri. Figure 27 shows a higher concentration of active amyl acetate and isoamyl acetate for men-tioned Kveik. These compounds have an aroma that is considered to be banana-and banana/pear-like. Two assessors noted that Idun tasted like banana or was

The sensory analysis was only performed with the the boxed in values in Figure 27, Rivenes and Raftevold yeast was brewed in experiment 2, and did not take part in the sensory analysis. WLP001 has a higher concentration of all observed alcohols.

The esters are reduced, but for some still larger for the fermentation of WLP001, isoamyl acetate (Sigmund and Stranda equal WLP001), active amyl acetate and ethyl hexanoate are larger for the Kveik. It does not seem to be a correlation between the sensory analysis (Table 9), and the difference in concentration when compared to WLP001 (Figure 27).

The threshold for flavor common flavor compounds found in beer is given in Table 2, these thresholds can be compared to the concentrations in the samples (Table 21 - 26 Appendix A.1). The data are compared, and given in Figure 28

Figure 28: Comparing detected concentration of flavors with reference values, red values are below the taste threshold, green values are above the threshold for beer in experiment 1 and 2. Highlighted values (Orange) are Kveik used in the Duo-trio test.

1-propanol is below the reported threshold value of 800 ppm for all Kveik strains, isobutyl alcohol is above the taste threshold in pure Hornindal at^◦C, Rivenes with contaminant at 19 ^◦C and WLP 001 at 19 (batch 1) and 30 ^◦C. Sigmund and Idun are below the threshold of active amyl alcohol. Isobutyl acetate is below the taste threshold for Hornindal + contaminant at 19^◦C. Many strains are below the threshold of ethyl decanoate.