Welcome to Wine Flavor 101A December 10, 2010

Overview of Fermentation Issues Linda F. Bisson Department of Viticulture and Enology University of California, Davis, CA

Off-Characters Found in Wine  Can originate in vineyard  Can derive from microbial activity  Can come from conditions of aging

Microbial Off-Characters  Pre-fermentation  During fermentation  Post-fermentation

Microbial Off-Characters  Pre-fermentation  During fermentation  Post-fermentation

Pre-Fermentation Off-Characters  Derive from the metabolic activities of non- Saccharomyces yeasts and bacteria  Increased impact with rot  Increased impact with hang time  Juice and must processing can encourage pre-fermentation character formation

Pre-Fermentation Processing  Lower temperatures: favor non- Saccharomyces yeasts  Low, no or late sulfite additions: favor both non-Saccharomyces yeasts and bacteria  Warm temperatures: favor bacteria  Oxygen exposure: favors both non- Saccharomyces yeasts and bacteria

Pre-Fermentation Processing  Lower temperatures: favor non- Saccharomyces yeasts –Cold soak/maceration (reds) –Cold settling (whites) –See bloom of Hanseniaspora/Kloeckera

Pre-Fermentation Processing  Low, no or late sulfite additions: favor both non-Saccharomyces yeasts and bacteria –Favors growth of both wild lactics and acetic acid bacteria –Favors growth of non-Saccharomyces yeasts

Pre-Fermentation Processing  Warm temperatures: favor bacteria –Cap management strategies –Refrigeration capacity

Pre-Fermentation Processing  Oxygen exposure: favors both non- Saccharomyces yeasts and bacteria –All organisms benefit from presence of oxygen –Obligate aerobes not inhibited

Types of Pre-Fermentation Characters  Esters  Acids _______________________________  Higher alcohols  S-compounds  Aldehydes

Microbial Off-Characters  Pre-fermentation  During fermentation  Post-fermentation

Fermentation Off-Characters  Esters  S-compounds ___________________________________  Higher alcohols  Acetaldehyde  Higher aldehydes  Volatile acids

Fermentation Off-Characters  Influenced by yeast strain  Impacted by growth conditions  Affected by juice composition

Fermentation Off-Characters  Influenced by yeast strain –Different strains vary ten-fold or more in compound production within dynamic range of odor detection –Strains dominate fermentation with differing efficiencies

Fermentation Off-Characters  Impacted by growth conditions –Volatilization of compounds »Temperature »Head space –Nutrient availability »Nitrogen »Micronutrients »Oxygen –Microbial competition »Sulfite use »Inoculation practices

Fermentation Off-Characters  Affected by juice composition –Availability of precursors –pH –Presence of stressors »High sugar/high ethanol »Previous microbial history

Today’s Program  Ester Formation and Ester Taints  Impact of Inoculation Level  Sulfur Compounds in Wine