Microbial spoilage
Microbial spoilage refers to the deterioration of wine caused by unwanted activity of yeasts, bacteria, or moulds that develop under certain winemaking or storage conditions. Unlike the controlled organisms used in fermentation, spoilage microbes can produce undesirable aromas, flavours, and textures that compromise both quality and commercial value.[1]
Causes and Organisms
The organisms most commonly associated with microbial spoilage are wild yeasts, lactic acid bacteria, and acetic acid bacteria. Species of Brettanomyces are particularly notorious for imparting aromas described as “barnyard” or “medicinal”.[2] Lactic acid bacteria such as Lactobacillus and Pediococcus may cause off-flavours, excessive volatile acidity, or slimy textures when they grow uncontrolled. Acetic acid bacteria, including Acetobacter, can oxidise ethanol into acetic acid, giving wine an unpleasant vinegar character.
Mould growth, although less frequent, can occur on poorly cleaned cellar equipment or in barrels with excessive humidity. These organisms can produce earthy or musty aromas, further diminishing wine quality.[3]
Environmental conditions also play a crucial role. Warm temperatures, residual sugar, insufficient sulphur dioxide, and poor sanitation all provide opportunities for spoilage organisms to proliferate. Wines with lower alcohol, such as unfinished fermentations or lightly fortified examples, are particularly vulnerable.
Impact on Wine
The sensory effects of microbial spoilage range from subtle to severe. Brettanomyces may impart faint spicy or smoky notes at low levels but can dominate the wine with leathery or animal-like odours when populations increase. Lactic acid bacteria can generate diacetyl, producing buttery aromas, or exopolysaccharides, leading to an unpalatable viscosity sometimes referred to as “ropy” wine.[4]
Other changes include turbidity or haziness from microbial growth, unintended refermentation in bottled wine, and the production of excessive volatile acidity. These faults not only alter the organoleptic profile but can shorten shelf life and erode consumer confidence. Economic consequences are significant: contaminated batches may need to be discarded or heavily discounted, and reputation damage can impact long-term market position.
Prevention and Control
Control of microbial spoilage begins with vigilant cellar hygiene. Thorough cleaning of tanks, barrels, and bottling equipment reduces the risk of contamination. Proper management of oxygen exposure is essential, since many spoilage bacteria thrive under aerobic conditions.[5]
Sulphur dioxide remains the principal preservative used in winemaking, inhibiting microbial growth while also protecting against oxidation.[6] Additional protective measures include maintaining adequate alcohol levels, controlling pH, and minimising residual sugar. For wines at risk, sterile filtration and pasteurisation provide further assurance of stability.
Some modern wineries use oxygen management techniques such as micro-oxygenation to enhance tannin polymerisation and stability, but careful calibration is required to avoid creating conditions favourable to spoilage. Research continues into natural antimicrobial agents, such as lysozyme and chitosan, although these remain complementary rather than replacements for established practices.
See also
References
- ↑ Robinson (ed.), The Oxford Companion to Wine, Oxford University Press, 2015.
- ↑ Jackson, Wine Science: Principles and Applications, Academic Press, 2020.
- ↑ Ribéreau-Gayon et al., Handbook of Enology, Vol. 1, Wiley, 2006.
- ↑ AWRI, “Wine faults: microbial spoilage”, awri.com.au.
- ↑ Jackson, Wine Science: Principles and Applications, Academic Press, 2020.
- ↑ Ribéreau-Gayon et al., Handbook of Enology, Vol. 1, Wiley, 2006.