🍇 Wine Microbiology · Smart Quiz

📘 Study Notes

Review these notes thoroughly before starting the quiz. All questions are based on this content.

🔬 Key Microorganisms

• Saccharomyces cerevisiae: main alcohol producer, tolerates 15-17% ABV, produces desirable esters.
• Non-Saccharomyces (Hanseniaspora, Candida): initiate fermentation, add complexity, but outcompeted.
• Oenococcus oeni: performs malolactic fermentation (MLF) → converts malic acid → lactic acid.
• Acetobacter / Gluconobacter: spoilage, oxidizes ethanol → acetic acid (vinegar).
• Brettanomyces: spoilage yeast → barnyard/band-aid off-flavors (4-ethylphenol).
• Lactobacillus/Pediococcus: can cause ropy slime or mousey off-flavors (spoilage).

📌 Fermentation Stages & Process

• Alcoholic fermentation: Yeasts (mainly S. cerevisiae) convert sugars → ethanol + CO₂ + heat.
• Malolactic fermentation (MLF): O. oeni converts sharp malic acid → softer lactic acid → decreases acidity, adds buttery/creamy notes.
• Aging on lees: yeast autolysis (dead yeast breakdown) releases mannoproteins → mouthfeel, brioche flavor.
• Stuck fermentation: premature stop before sugar conversion (e.g., nutrient deficiency).

⚙️ Control & Spoilage Prevention

Method	Target / Mechanism
SO₂ (sulfur dioxide)	Antimicrobial: suppresses wild yeasts, Acetobacter, LAB
Low pH (<3.5)	Inhibits spoilage bacteria growth
Anaerobic conditions (no O₂)	Prevents Acetobacter (needs oxygen)
Sterile filtration (0.2-0.45 µm)	Physically removes all microbes before bottling
Inoculation (starter cultures)	Predictable fermentation, alcohol control, flavor targeting

🧪 Common Spoilage & Vocabulary

• Acetobacter → vinegar taint (sharp, sour).
• Brettanomyces → barnyard, band-aid.
• Pediococcus/Lactobacillus → ropy / viscous wine.
• Must: unfermented grape juice + skins/seeds.
• Lees: dead yeast cells; Autolysis: breakdown of dead yeast.
• MLF is standard for reds (high malic acid) → softening; whites like Riesling often skip MLF to retain crispness.

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Tip: Always remember: S. cerevisiae = alcohol, O. oeni = MLF, Acetobacter = vinegar, sterile filtration = bottle stability.