Institute of Brewing and Distilling

Transcription

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2 Institute of Brewing and Distilling Asia Pacific Section s 32 nd Convention Melbourne, Victoria March 25 th -30 th 2012 Fermentation The Black Box of the Brewing Process A Concept Revisited Graham G. Stewart G.G.Stewart Associates Cardiff, Wales. Nottingham University Nottingham, England. Heriot-Watt University Edinburgh, Scotland.

3 The Three Stages of the Brewing Process Wort Preparation Malting Mashing Lautering Boiling and gravity adjustment Protein Wort clarification Fermentation Post-fermentation Processing Aging/Lagering Blending Filtration Dilution Carbonation Packaging

4 Areas Discussed in the Original Black Box Paper that Required Further Research Influence of wort sugar spectrum particularly maltose and maltotriose. High gravity brewing and fermentation for capacity and sustainable benefits. Yeast flocculation. Diacetyl management. Stress effects on yeast. Novel molecular biology methodology.

5 Areas to be considered: Analytical instrumentation. Diacetyl management. Stress effects on yeast. Novel molecular biology methods and yeast taxonomy. Stratified fermentation in vertical fermenters. Centrifuges for yeast cropping.

6 DIACETYL MANAGEMENT

7 Mechanism of Diacetyl Production by Yeast Ethanol Carbohydrate Pyruvate Acetic Acid Ethanol α-acetolactate Acetic Acid α-acetohydroxybutyrate Enzymatic Conversion Passive Diffusion Plasma Membrane Valine leucine Isoleucine Non-Enzymatic Decomposition α-acetolactate α-acetohydroxybutyrate Diacetyl Pentanedione

8 Mechanism of Diacetyl Reduction by Yeast Diacetyl Diacetyl Plasma Membrane Acetoin Enzymatic Conversion Plasma Diffusion Butanediol Acetoin Butanediol

9 Mode of Action of Alpha Acetolactate Decarboxylase Alpha-acetolactate Acetoin

10 Effect of Alpha Acetolactate Decarboxylase (ALDC) on Diacetyl Metabolism in Fermenting Wort Diacetyl mg/l Control Yeast 20 ADU/L 40 ADU/L 60 ADU/L Fermentation time (hours)

11 Effect of Alpha Acetolactate Decarboxylase (ALDC) on Wort Fermentation Rate and Extent Degree plato Control Yeast 20 ADU/L 40 ADU/L 60 ADU/L Fermentation time (hours)

12 Effect of Alpha Acetolactate Decarboxylase (ALDC) Expression in a Brewing Yeast Strain on Diacetyl Metabolism During Wort Fermentation Diacetyl (mg/l) ALDC Yeast Control Yeast Fermentation time (hours)

13 Effects of Alpha Acetolactate Decarboxylase (ALDC) Expression in a Brewing Yeast Strain on Overall Fermentation Rate During Wort Fermentation ALDC Yeast Control Yeast Degree plato Fermentation time (hours)

14 STRESS EFFECTS ON BREWER S YEAST STRAINS

15 Effects of Stress on Brewer s Yeast Strains Decrease in viability and vitality. Depletion of glycogen and increases in trehalose. Excretion of proteinase A and other proteinases. Shear of cell wall components, principally mannan resulting in changes in flocculation characteristics. Development of intracellular shock proteins [also called heat shock proteins (hsp) but not only formed during heat shock conditions]. Increases in respiratory deficient and other mutants.

16 Stress Factors Which Promote Proteinase A Release Osmotic pressure Acid washing Ethanol concentration Yeast Thermal stress (hot and cold) Mechanical stress

17 TAXONOMY OF ALE AND LAGER YEAST STRAINS

18 Evolution of the Scientific Names of Ale and Lager Yeast Species Ale Saccharomyces cerevisiae. Saccharomyces cerevisiae (ale type). Lager Saccharomyces carlsbergensis. Saccharomyces uvarium. Saccharomyces uvarium (carlsbergensis). Saccharomyces cerevisiae (lager type). Saccharomyces pastorianus.

19 Ale/Lager Yeast Strains The Saccharomyces sensu stricto group S. bayanus low 72% S. paradoxus low S. pastorianus 50% 50% S. cerevisiae

20 Lager Yeast from Patagonia? Saccharomyces pastorianus is a yeast species created by the fusion of Saccharomyces cerevisiae and Saccharomyces eubayanus. Saccharomyces eubayanus exists in the forests of Patagonia and has not been found in Europe. The genome sequence of Saccharomyces eubayanus is 99.5% identical to the non- Saccharomyces cerevisiae portion of the Saccharomyces pastorianus genome sequence. The unique location of Saccharomyces eubayanus in the Patagonian forests is questionable!

21 Some Examples of Potential Uses of Genetic Applications in Brewing Yeast Strains Yeast with α-acetolactate decarboxylase for diacetyl management. Yeast strains with multiple maltose genes for rapid wort fermentation. Yeast producing glucoamylase (STA/DEX genes) to produce beer with reduced dextrin concentration. Zymocidal (killer) yeasts that inhibit wild yeast infection wine yeast strains. Detection of contaminants.

22 STRATIFIED FERMENTATIONS IN CYLINDROCONICAL FERMENTERS

23 Cylindroconical Fermenters

24 Stratified Fermentations A stratified fermentation is where two or more separate and distinct fermentations occur in a fermenter at the same time. These fermentations are layered and marked by boundary zones. Each fermentation has an individual density, temperature and yeast cell count. A number of conditions favour development of stratification: - Addition of fresh, unyeasted wort to an active fermentation. - Pitching all the yeast in the first brew during a multibrew fermentation. - High density and/or high temperature differences between added wort and the fermenting wort already in the fermenter. - Fermenter design especially cylindroconical fermenters.

25 Stratified Fermentations (cont d) There are several tools available to detect stratified fermentations: - Sudden temperature change occurs hours after addition of the last brew signals possible stratification formation. - At the same time, there are changes in CO 2 generation. A number of breweries and research laboratories have assessed the use of rotary jet mixing technology in order to avoid stratified fermentations. Results are positive with more rapid VDK adjustment, enhanced beer quality, stability and fermentation time resulting in increases in production capacity without significant capital investment.

26 CENTRIFUGES IN BREWING

27 Centrifuges in Brewing Centrifuges have a number of applications during the process but the cropping of yeast with a centrifuge at the end of primary fermentation is currently its principal function. Does the passage of a brewer s yeast strain through a disc stack centrifuge of differing operating G-forces have a negative effect on: - Cell viability. - Cell vitality. - Beer physical and foam stability?

28 The ICBD 2hL Brewing Pilot Plant

29 The Disc Stack Centrifuge (5hL/hour)

30 Centrifuges in Brewing (Cont d) Cropping of yeast at the end of primary fermentation enhances process efficiency but it exposes yeast to shear stress. Yeast viability decreases as it is recycled through the centrifuge. Beer haze increases due to mannan residues as a result of shear stress. The physiological state of the yeast alters and the intracellular carbohydrates glycogen and trehalose are depleted during centrifugation. The passage of yeast cells through a stack centrifuge can adversely influence yeast physiological properties and beer stability.

31 Scanning Electron Microscopy of an Ale Strain A. Cells prior to passage through a disc centrifuge. B. Cells following passage through a disc centrifuge. A B

32 The Three Stages of the Brewing Process Wort Preparation Malting Mashing Lautering Boiling and gravity adjustment Protein Wort clarification Fermentation Post-fermentation Processing Aging/Lagering Blending Filtration Dilution Carbonation Packaging

33 The Three Stages of the Brewing Process Wort Preparation Malting Mashing Lautering Boiling and gravity adjustment Protein Wort clarification Fermentation X Post-fermentation Processing Aging/Lagering Blending Filtration Dilution Carbonation Packaging

34 Summary During the last two decades advances in the following areas have contributed to our knowledge of the following fermentations: Diacetyl management. Wort sugar uptake and metabolism. Stress effects on yeast. Yeast taxonomy and the application of molecular biological methods. Stratified fermentations in cylindroconical fermenters. Centrifuges in brewing.

35 Acknowledgements Many colleagues have contributed to the research described in this paper for which I am very grateful. The invaluable assistance and support of Anne Anstruther in developing this presentation is gratefully acknowledged.

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