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Acetic Acid Bacteria and Other Taints Wine Flavor 101 January 2017
Linda F. Bisson Department of Viticulture and Enology University of California, Davis
Wine Off-Characters of Microbial Origin
Off-colors Off-flavors Hazes/cloudiness Sediment/precipitates
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Source of Microbial Off-Characters
Vineyard flora Winery flora Fermentation microbes – Saccharomyces – Lactic acid bacteria Spoilage microbes – Acetic acid bacteria – Lactic acid bacteria – Flor yeasts – Brettanomyces – Non-Brett Spoilage Yeasts
Off-Characters
Same off-character may come from different sources (acetaldehyde) Some off-characters arise only in specific chemical/microbial environments Compound(s) responsible for some taints are unknown Best course of action: not getting them in the first place!
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ACETIC ACID BACTERIA
Acetic Acid Bacteria in Wine
Pre-fermentation issues During fermentation issues Post-fermentation issues
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Pre-Fermentation Acetic Acid Bacteria
Normal residents of berry surfaces Increased impact with rot Normal residents of winery surfaces Some resistant to sulfur dioxide due to metabolism
Energy Sources for Microbes in Wine
Carbohydrate bond energy (Saccharomyces, other yeasts) Thermodynamic energy from proton movements due to low pH (Lactic acid bacteria) Electrochemical energy from proton/ electron movements particularly as impacted by phenolic compound consumption of oxygen: a rich Redox environment (Acetic acid bacteria)
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Acetic Acid Bacteria
Have a simple respiratory chain leading to formation of ATP A set of membrane bound dehydrogenases channel electrons to the respiratory chain Have a limited proton translocation capacity as this inhibits energy capture from electron movements
Acetic Acid Bacteria
Specialists in capture of electrochemical energy: “oxidative fermentation” Can use the same energy sources as yeast and lactic acid bacteria but have become specialists in generating energy from partial oxidation reactions Results in low biomass production but with a high impact on the environment
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“Gluconobacter oxydans is unsurpassed in its ability to incompletely oxidize a variety of carbohydrates, alcohols and related compounds.”
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Acetic Acid Bacteria in Juice
Use oxidation of glucose to gluconic acid and fructose to oxy-fructose and subsequent higher oxidized compounds to generate energy Acetic acid not produced Oxidized sugars bind sulfur dioxide Different species found in juice versus wine
Acetic Acid Bacteria in Wine
Use oxidation of ethanol to acetaldehyde and acetic acid to generate energy Requires low levels of oxygen to create permissive redox conditions Ethyl acetate forms from the reaction of ethanol and “mobilized” acetic acid Wine species are adept at oxidation of ethanol
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Ethanol Consumption
Ethanol deyhdrogenase – Ethanol oxidized to acetaldehyde Acetaldehyde dehydrogenase – Acetaldehyde oxidized to acetic acid
Acetyl-CoA oxidation to CO2 – Some, but not all, strains can oxidize acetic acid – Regeneration of CoA results in ethyl acetate formation
Acetic Acid Bacteria in Wine
Ethanol is plentiful Limited by redox conditions of wine Oxygen limitation reduces options but does not prevent metabolism if other acceptors are present Since growth demands are not high, they are not that susceptible to agents that inhibit growth of bacteria: ethanol Are susceptible to agents that interfere with redox conditions: sulfite
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Acetic Acid Bacteria Taints
Acetic acid: pungent, chemical Ethyl acetate: glue, nail polish, nail polish remover Gluconic acid: sweet acid taste distinct from sugar sweetness
Juice Lactic Acid Bacteria
Form different compounds from mid and post-fermentation metabolism Fructophilic lactic acid bacteria can produce mannitol from fructose and to a much lesser extent sorbitol from glucose Mannitol taint in wine: sugar alcohol sweetness with an irritating finish
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Mannitol Production by Lactic Acid Bacteria
Fructophilic Lactic Acid Bacteria
L. kunkeei most common juice fructophilic LAB Can produce relatively high levels of mannitol (10-15 g/L) May be re-consumed by Saccharomyces
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AAB/LAB Tasting
Glass 1: Control Cabernet Sauvignon Glass 2: Acetic acid (low) (200 mg/L) Glass 3: Acetic acid (high) (2 g/L) Glass 4: Ethyl acetate (50 mg/L) Glass 5: Gluconic acid (2g/L) Glass 6: Mannitol (2g/L)
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