Impact of Yeast Strain Diversity

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Impact of Yeast Strain Diversity. Lucy Joseph Department of Viticulture and Enology UC Davis. Outline of Yeast Diversity. Overview of biological strain diversity Commercial yeast strains Choosing a yeast strain Native yeast strains Interaction with other yeast and fungi and bacteria. - PowerPoint PPT Presentation

Text of Impact of Yeast Strain Diversity

  • Impact of Yeast Strain DiversityLucy JosephDepartment of Viticulture and EnologyUC Davis

  • Outline of Yeast DiversityOverview of biological strain diversityCommercial yeast strains Choosing a yeast strainNative yeast strainsInteraction with other yeast and fungi and bacteria

  • What is a Strain?Strains are the same species of organism They have measureable differencesThese differences are consistent and inheritedStrains are often a clonal population (budding)Differences may be genetic or due to the expression of genetic material

  • How do Differences Arise?Genetic change on the chromosome either by sequence or positionGenetic difference in organelle DNA, example: mitochondrial or ribosomal DNAGenetic mutation in or loss or gain of extra-chromosomal DNAExtra copies of chromosomes, anueploid/polyploidHybrids between Saccharomyces speciesInherited transcriptional state, i.e. epigeneticInherited protein conformational state i.e. prion

  • Selection for DifferencesNatural variation occursUnfavorable variants selected againstFavorable variants more likely to survive and reproduceNew Strain

  • Domesticated vs. Wild Saccharomyces cerevisiaeWild Saccharomyces are found in the vineyard and in oak trees and soil near vineyardsDomesticated Saccharomyces are found in the winery and for sale from inoculant companiesDomesticated yeast are typically better suited for making wineThey are selected both naturally and purposefully to survive and thrive in the winery environment

  • Definition of Domesticatedspecies bred in captivity and thereby modified from its wild ancestors in ways making it more useful to humans who control its reproduction and (in the case of animals) its food supplyDiamond J (2002) Evolution, consequences and future of plant and animal domestication Nature, 418, 700707

  • Wine Yeast and Other Domesticated YeastLeGras et.al. Molecular Ecology (2007) 16:2091-2102.

  • Characteristics Selected For in WineAcid ToleranceTemperature rangeSulfite resistance Vineyard and WineryFermentation speedAlcohol toleranceNitrogen requirementCompetitiveness

  • What traits do you want in a yeast?

  • What traits do you want in a yeast?

  • Characteristics not Selected for in NatureSensory propertiesLow VA, SO2, H2SPositive ester productionEnhanced mouthfeelThose important in productionLow foam productionFlocculationML compatibility

  • What traits do you want in a yeast?

  • What traits do you want in a yeast?

  • Choosing a Yeast StrainConsider yeast as a tool for wine makingFactors to Consider:Grape varietalBrix and alcoholFermentation temperatureAdditionsProduction capacityWine making style ML, aging, micro-ox, etc.

  • Before Inoculation

  • Before Inoculation

  • Testing May Affect Your Yeast ChoiceIf you might add nitrogen or use a yeast that doesnt require high nitrogenIf other nutrients are lackingIf you should consider a yeast that tolerates high alcohol If you are concerned about H2S or SO2 production

  • Other factors for your considerations

  • Native FermentationsYeasts other than Saccharomyces can occur and complete fermentationsCommercial strains can persist in the wineryNative strains may have greater potential for change (instability)Potential for strains with undesirable characteristics to dominate and persistMultiple strain fermentations are more likely to occur

  • Stuck FermentationOnce a fermentation sticks it can be hard to un-stickSome strains do better than others at thisNative fermentations should be monitored more closely

  • Sensory DefectsThese may occur more often with native fermentationsMonitor closelyConsider inoculation at first signs of troubleThe point of inoculation is to get rapid and consistent fermentations

  • Mixed FermentationsPro:Wild yeasts can add complexity to winesMore than one strain of Saccharomyces could add complexity and unique characterDiverse population may handle stress betterCon:Competition between yeasts and strains can select for those with undesirable traitsStrains that grow well do not always produce the best wine

  • Other Microbe InteractionsSome yeasts are not compatible with ML conversionPossibly due to more complete utilization of nutrients leaving less for OenococcusHigh SO2 can inhibit MLLow pH can also prevent ML

  • Other Microbe InteractionsSpecialty wines like botrytized have specific issues, botrytized wines will have far more diverse flora making fermentation more of a challengeSparkling and sherry wines have another yeast fermentation during the second stage of production which must be compatible with the first yeast

  • SummaryBy Analogy.

  • Domesticated Organisms Retain Much Diversity

  • Strains are Bred for Specific ConditionsNo single strain does well under all conditionsNo single strain serves all purposes

  • Some Strains are Just More Pleasing to the Senses

  • Wild Strains Have the Most Diversity

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