Wine Fault

Lactobacillus

Microbial

Lactobacillus spoilage produces sour, cheesy, and sometimes mousy off-aromas when lactic acid bacteria grow outside controlled malolactic fermentation. The fault often appears in low-SO₂ or stuck wines with residual sugar.

Also known as: Lactic acid bacteria spoilage, LAB spoilage, Sauerkraut bacteria

Typical severity: Medium

Cause

Unwanted lactic acid bacteria (Lactobacillus and related LAB) metabolizing sugars and acids after primary fermentation.

How it occurs

Stuck ferments, high pH, low SO₂, and warm cellars allow LAB to proliferate when MLF is incomplete or unintended. Dirty hoses and unsanitized tanks are common entry points.

Prevention

Complete primary fermentation, control pH, maintain SO₂, inoculate MLF deliberately when desired, and enforce strict sanitation. Monitor malic acid depletion.

Descriptors created

Descriptors reduced

Commonly confused with

Common wine styles

Common grape varieties

Common regions

Related winemaking techniques

Serving implications

Beginner explanation

Controlled MLF is intentional; unwanted Lactobacillus growth smells sour or cheesy without the intended buttery integration.

FAQ

Is Lactobacillus the same as malolactic fermentation?
MLF uses beneficial LAB deliberately. Spoilage Lactobacillus grows uncontrolled and produces off-aromas beyond normal malic conversion.
Can filtration remove this fault?
Sterile filtration can remove bacteria before they spoil the wine, but sensory damage already done cannot be reversed.

Related ontology entities

See also

Fault identification guidance reflects common wine education practice and may vary by wine style, age, and context.