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Types of Native Fermentations Linda F. Bisson Wine Flavor 101 January 2016 Native Fermentations: Definitions The term “native” with respect to wine production has several meanings: – Not deliberately inoculated – No commercial yeast strains present – Only vineyard yeast present – Vineyard/winery resident yeast only present – No manipulation of native microbiota – Only autochthonous yeast present Source of “Native” Flora Vineyard Winery Early Both are sources of microbes in season grape microbiota may be most important but as microbes become established on winery surfaces, winery microbiota become more important Genetic data suggests winery microbes likely overwinter in the winery and build up from winery, not vineyard, biota And it all depends upon sanitation practices! Native Fermentations: Goals Complexity, complexity, complexity Non-Saccharomyces yeast and bacteria able to contribute to aroma, flavor and mouthfeel properties of the wine Slower fermentation of Saccharomyces contributes to aroma and flavor profile of wine Wines are more unique and appealing than they would be using a “generic” strain Enhanced varietal character due to hydrolases and other enzymes produced by a diverse microbiota or to production of aroma-enhancing compounds (matrix effects) Not Deliberately Inoculated No commercial inoculum No tank-to-tank inoculum May be “inoculated” by winery biota – Tank/barrel residents – Hoses/equipment residents Depending on sanitation practices may be conducted by vineyard biota No Commercial Yeast Strains Present Winery has never used commercial starters (ever) Winery has not introduced materials (bulk wines; used equipment) that has seen commercial starter cultures Winery may take steps to not be accidentally “inoculated” by natural starters from adjacent wineries Yeast lees returned to vineyard? Only Vineyard Yeast Present Challenging: requires intense sanitation program to eliminate winery residents each year Vineyard yeast variability from year to year both in numbers and types of strains should be evident Winery lees may or may not be put back in the vineyard Vineyard/Winery Resident Yeast Only Present Recognizes challenges of not developing winery “house” strains House strain lees may be added back to vineyard so origins the next season may be confounded No Manipulation of Native Microbiota No use of sulfur dioxide or other antimicrobial No additions of nutrients that would alter microbial dynamics No oxygen addition except that occurring during transfers No temperature control that would alter microbial dynamics Only Autochthonous Yeast Present Autochthonous: “originating in the place found” Strains present are not just found in the wild but originated in that region Challenging with wine yeast as yeast DNA analyses have shown “migration patterns” for specific strains Issues: – If one generates a “house autochthonous” strain and uses it as an inoculum, is it still “native”? – Should “heritage yeast” be its own category of fermentation type? The Negative Impacts of Native Microbiota Arrest of alcoholic/ML fermentations Spoilage character formation – From the non-Saccharomyces microbes – From Saccharomyces due to enhanced competition for nutrients and growth factors Loss of varietal character – Degradation of varietal aroma/flavor compounds – Modification of varietal aroma/flavor compounds – Masking of varietal impact compounds When Are Negative Impacts Likely? Condition of fruit: high incidence of rot/damage in vineyard High insect presence Lack of a robust native strain of Saccharomyces ( a trade-off between sanitation practices and use of “house” strains Deficiencies in grape composition: nutritional stress Undesirable vineyard residents: the dreaded “bad lactics” Condition of the Fruit Damaged Clusters – Rot amplifies acetic acid bacteria – Mold metabolites may be present Uneven Ripening/Raisining – Leads to differences in flora on the surfaces of the fruit Presence of Material Other than Grape – Soil, leaves, bark: all contain microbes – Some of these microbes can persist early in fermentation Timing of Harvest During ripening the berry surface flora change – More seepage from the berry providing nutrients – Yeast population continues to increase in relative numbers postveraison Aerobic basidiomycetes are replaced by the fermentative ascomycetes – Consume available oxygen rapidly – Create localized anaerobic zones – Produce toxic waste products Aerobic bacilli and pseudomonads replaced by acetic and lactic acid bacteria – Produce toxins and toxic waste products Factors Impacting Biota and Persistence pH Temperatures of holding or processing: everything is a selection Oxygen exposure Nutrient level and diversity of nutritional components The starting biota and strains present Native Fermentations: Styles 100% native: no additions of any microbes ever Native yeast but with ML inoculation Native Saccharomyces only or native nonSaccharomyces? (manipulate biota using sulfur dioxide) Partial natives: inoculated at some point (the insurance policy method) Manipulated microbiota “natives” Manipulated Microbiota Sulfur dioxide or other antimicrobial agent used Temperature of pre-incubation/fermentation pH adjustment or selection Level of aeration Nutrient addition practices Inoculation with non-Saccharomyces yeasts and bacteria Partial Natives Temporal inoculation: after x days Inoculation at a specific Brix/ethanol level Inoculation at “first sign of trouble” Addition of SO2 to arrest non-Saccharomyces biota Selective feeding of Saccharomyces population The VEN124L Trial: Test the impact of timing of inoculation of a commercial strain of Saccharomyces Used Albariño No sulfur dioxide No nutrient additions Used a neutral yeast: EC1118 Treatments ● Control: inoculated with EC1118 at 0 hours ● 24hrs: inoculated with EC1118 at 24 hours ● 48hrs: inoculated with EC1118 at 48 hours ● 72hrs: inoculated with EC1118 at 72 hours ● 96hrs: inoculated with EC1118 at 96 hours ● Native: no inoculation, left to ferment with native yeast Fermentation Data Inoculation Timing Tasting: Glass 1: Glass 2: Glass 3: Glass 4: Glass 5: Glass 6: Inoculated Time 0 Inoculated 24 hrs. Inoculated 48 hrs. Inoculated 72 hrs. Inoculated 96 hrs. Uninoculated
