RELATIONSHIPS BETWEEN THE SPEED OF FERMENTATION AND LEVELS OF FLAVOUR COMPOUNDS POST- FERMENTATION

Transcription

1 1 RELATIONSHIPS BETWEEN THE SPEED OF FERMENTATION AND LEVELS OF FLAVOUR COMPOUNDS POST- FERMENTATION Maria Josey, James Bryce and Alex Speers Young Scientists Symposium 2016 Chico, California

2 Yeast Derived Flavour Compounds in Beer 2 Iso amyl acetate Ethyl hexanoate Ethyl Octanoate 3 Methyl butanol 2 Methyl butanol Iso butanol Butanedione Pentanedione Esters Higher Alcohols Vicinal Diketones (VDKs)

3 Fermented Sugars Maltose Glucose Fructose Maltotriose Sucrose Invertase Yeast s Metabolic Pathway Simplified Amino acids 3 Glucose Fructose Hexose transporter Glucose Fructose Ketoacids Amino acids Maltotriose α-glucosidase Maltose Pyruvate Acetaldehyde Ethanol cetaldehyde Ethanol Acyl-CoA Fatty Acyl-CoA Fatty acids Fatty acids TCA cycle mitochondrion Esters Esters Higher alcohols a-acetolactate 2,3-butanediol Diacetyl Higher alcohols a-acetolactate Diacetyl Figure 1. A visual of the major metabolic pathways in the yeast cell (Journal of the Institute of Brewing Volume 120, Issue 3, pages , 10 JUN 2014 DOI: /jib.145http://onlinelibrary.wiley.com/doi/ /jib.145/full#jib145-fig-0001)

4 A Few Fermentation Variables Studied That Impact Flavour 4 Pitching Rate Higher pitching rates associated with lower levels of butanedione and pentandione (Erten et al., 2007) Wort Gravity Higher wort gravity increased acetate ester levels increased (Verbelen et. al, 2009) Wort Aeration Lower aeration showed lower esters (Brown, 2003) Petite Mutations Mutated cells vary flavour levels in the final beer product (Ernandes, 1993)

5 Experimental Design 5 Wort Prep Malt bill: Lager malt (73%), rice (24%), Crystal (or Munich)(2%) Hops: Admiral and First Gold Fermentation Volume: 1.6 hl Yeast strain: Industrial lager Original Gravity: 12 P Sampling: Density Beer sample at h=122 Yeast Crop Storage temperature: 11 C Storage time: 6 h ABV: 4.3% Re-pitched

6 Nonlinear Logistic Model 6 P i Density ( P) Nonlinear logistic describing density attenuation during fermentation B P t = P e Pi P + 1+ e e B( t M ) 3 M P e Time (hr) Figure 2. Fermentation Nonlinear Logistic

7 Why use this model? 7 To best-fit the line through data, computer scores fit by summing error (sum of squares). Repeatedly guesses new line lowering error. Plato ( o P) Residual Σ Residual 2 = RSS = error Time (h)

8 8 15 Density Attenuation of Re-pitched Fermentations Density trends for the nine re-pitched fermentations Density ( P) Time (hr) 9 Figure 3. Modelled density attenuation curve for nine re-pitched fermentations. The re-pitched number is noted by individual colours

9 9 Density trends for the re-pitched fermentations With fermentations with Crystal malt Most curves significant (p>0.05) with the exception of 1 and 9. Density ( P) Density Attenuation of Re-pitched Fermentations Time (hr) Figure 4. Modelled density attenuation curve for re-pitched fermentations that contained 2% Crystal malt

10 10 Density trends for the re-pitched fermentations With fermentations with Munich malt Fermentation visually slower than fermentations containing 2% Crystal Density ( P) Density Attenuation of Re-pitched Fermentations Time (hr) Figure 5. Modelled density attenuation curve for re-pitched fermetations that contained 2% Munich malt

11 11 Density trends for the nine re-pitched fermentations Density ( P) Density Attenuation of Re-pitched Fermentations Time (hr) Figure 3. Modelled density attenuation curve for nine re-pitched fermentations. The re-pitched number is noted by individual colours

12 Flavour Compounds and Re-pitched Number 12 No obvious trends related to the repitched number 0.7 Butanedione 20 Ethyl Acetate mg/l 0.5 mg/l Re-pitched Number Re-pitched Number Figure 6. Butanedione (1) and ethyl acetate (2) levels present at the end of fermentation for nine re-pitched fermentations

13 Flavour compounds correlated to the function of the slope (B) at the midpoint 13 Ethyl Hexanoate Ethyl Octanoate Ethyl Octanoate Ethyl hexanoate mg/l R 2 = mg/l R 2 = B B Figure 7. The function of the slope (B) at the midpoint of the fermentation correlated to ethyl hexanoate (1) and ethyl octanoate (2) at the end of fermentation

14 Similar trends found with other flavour compounds (i.e. ethyl butyrate, and iso butyl acetate Ethyl butyrate Ethyl butyrate 0.06 Iso butyl acetate Iso butyl acetate 1 2 mg/l R 2 = mg/l R 2 = B B Figure 8. The function of the slope (B) at the midpoint of the fermentation correlated to ethyl butyrate (1) and iso butyl acetate (2) at the end of fermentation

15 Effect that the function of the slope (B) has on butanedione and pentanedione levels Pentanedione Pentanedione 0.7 Butanedione Butanedione 1 2 mg/l Are correlations found due to mg/l higher B values having more 0.5 Rcompleted 2 = fermentations? R 2 = B B Figure 9. The function of the slope (B) at the midpoint of the fermentation correlated to pentanedione (1) and butanedione (2) levels at the end of fermentation

16 16 Apparent Degree of Fermentation (ADF) 0.08 Ethyl butryate 0.07 R 2 = AAA = P 0 P 122 P mg/l ADF calculated at P ADF Figure 10. The correlation between ethyl butyrate levels at the end of fermentation and the Apparent Degree of Fermentation (ADF)

17 17 Table 1. The goodness of fit R 2 for the stated flavour levels compared to the function of the slope at the midpoint during fermentation (B) or compared to the ADF at t=122 of the fermentation. The data highlighted in red has the stronger correlation of the two tested. Flavour Coumpounds B vs. Flavours R 2 ADF vs. Flavours R 2 Acetaldehyde Acetone Ethyl acetate Isobutyl acetate Ethyl butyrate Propan-1-ol Isobutanol Iso amyl acetate Methyl butanol Methyl butanol Ethyl hexanoate Ethyl Octanoate Butanedione Pentanedione Key: Higher R 2 Significant (p>0.05) Not Significant

18 Summary and Applications 18 The function of the slope (B) is a better predictor than the ADF to correlate to certain flavour levels There is a correlation between the speed of the fermentation and various flavour compounds Butanedione, pentanedione, ethyl hexanoate, ethyl octanote, iso amyl acetate, iso butyl acetate, ethyl butyrate, 2 methyl butanol, Some flavour compounds were not significantly impacted by the slope Acetaldehyde, ethyl acetate, acetone, 3-methyl butanol, isobutanol, and propan-1-ol Possible to tailor to individual fermentations

19 Acknowledgements 19 IBD Jim MacKinley Analytical Services, Heriot Watt University Graham McKernan Brewer Manager, Heriot Watt University

20 References 20 American Society of Brewing Chemists. Methods of Analysis, 2012, 12th ed., Yeast-14 Miniature Fermentation Assay. The Society, St. Paul, MN. Brown, A. K., & Hammond, J. R. M. (2003). Flavour control in small-scale beer fermentations. Food and Bioproducts Processing, 81(C1), doi: / Ernandes, J. R., Williams, J. W., Russel, I., & Stewart, G. (1993). Respiratory deficiency in brewing yeast strains Effects on fermentation, flocculation, and beer flavor components. Journal of the American Society of Brewing Chemists, 51(1), Erten, H., Tanguler, H., & Cakiroz, H. (2007). The Effect of Pitching Rate on Fermentation and Flavour Compounds in High Gravity Brewing. Journal of the Institute of Brewing, 113(1), doi: /j tb00259.x He, Y., Dong, J., Yin, H., Zhao, Y., Chen, R., Wan, X.,... Chen, L. (2014). Wort Composition and its Impact on the Flavour-Active Higher Alcohol and Ester Formation of Beer - A review. Journal of the Institute of Brewing, 120, Verbelen, P. J., Dekoninck, T. M. L., Saerens, S. M. G., Mulders, S. E. V., Thevelein, J. M., & Delvaux, F. R. (2009). Impact of Pitching Rate on Yeast Fermentation Performance and Beer Flavour. Applied Microbiology and Biotechnology, 82,

21 Thank you for listening 21

22 Calculating the slope at M 22 Nonlinear logistic describing density attenuation during fermentation P0 Density ( P) B P122 Slope of the tangent at M: B (P 0 P 122 ) 4 Time (hr) Figure 1.2 Fermentation Nonlinear Logistic

23 Ethyl Hexanoate and Ethyl Octanoate 23 Transfer to medium decreases as the larger the fatty acid chain is Transfer is temperature dependent Ethyl Hexanoate Ethyl esters: MCFA + Ethanol Stress Indicator (?) Ethyl Octanoate

24 24 Metabolic Pathway