Details of defects associated with malolactic fermentation (MLF).
| Defect | Conditions increasing susceptibility | Compounds modified | Compounds produced | Sensory effects | Source |
|---|---|---|---|---|---|
| Increased pH | High pH, high climatic temperatures, uncontrolled/spontaneous MLF, malic acid addition | Malic acid | Lactic acid; ethyl lactate and ethyl acetate; propanoic acid; 2-methyl; 3-hydroxy-2,2,4-trimethylpentyl ester | Flavors described as lactic, wet wool/wet dog, rancid, cheesy, sweaty | Keng et al. 2025 |
| Color instability | High pH, high climatic temperatures, oxygen exposure | Anthocyanins | Glycosidases, anthocyanidins, monomeric anthocyanins | Reduced color intensity, oxidation with increased pH | Tofalo et al. 2021, Burns and Osborne 2013, Bartowsky and Krieger-Weber 2020 |
| Increased alcohol/fusel alcohols | High pH, high climatic temperatures, high alcohol, oxygen exposure | a-Keto acids | Fusel aldehydes, fusel alcohols | Burning/tingling sensation; flavors described as solvent-like, boozy, and bitter | Hazelwood et al. 2008, Lerm et al. 2010, de-la-Fuente-Blanco et al. 2024 |
| Ropiness | High pH, high climatic temperatures, more common in white wine | Glucose | Extracellular polysaccharides, glucan | Increased viscosity, gelatinous substances | Ciezack et al. 2010, Dimopoulou and Dols-Lafargue 2021 |
| Mousiness | High pH, oxidative conditions, uncontrolled/spontaneous MLF | Amino acids | N-heterocyclic compounds, 2-acetyltetrahydropyridine, 2-acetyl-1-pyrroline | Mousiness | Costello et al. 2001 |
| Citric acid degradation | High pH, uncontrolled MLF | Citric acid | Acetic acid, diacetyl, acetoin | Volatile acidity, buttery and nutty flavors | Nielsen and Richelieu 1999 |
| Tartaric acid degradation | High pH | Tartaric acid | Lactic acid, acetic acid | Increased pH, volatile acidity, effervescence, lactic flavors | Krumperman and Vaughn 1966 |
| Glycerol degradation | High pH (>4.0), high climatic temperatures, high postharvest temperatures (>20°C), low alcohol/low fermentable sugar, press wines, wines with prolonged lees aging | Glycerol | 3-Hydroxypropionaldehyde, acrolein, acetic acid | Bitterness, volatile acidity | Bauer et al. 2010, Popescu-Mitroi et al. 2014 |