Wine Fault

Diacetyl Excess

Additional

Diacetyl excess occurs when buttery, butterscotch-like aroma from malolactic fermentation or bacterial spoilage overwhelms fruit and balance. Controlled diacetyl adds complexity in Chardonnay; excess reads as a sensory fault.

Also known as: Butter bomb, Diacetyl fault, Over-buttery

Typical severity: Medium

Cause

Elevated diacetyl from malolactic bacteria, Pediococcus, or delayed MLF without sufficient SO₂ post-MLF.

How it occurs

Warm MLF, high pH, and bacterial stress push diacetyl above integration thresholds. Pediococcus spoilage can amplify buttery character into fault territory.

Prevention

Monitor MLF temperature and timing, adjust SO₂ after MLF completes, and test for bacterial spoilage before bottling.

Descriptors created

Descriptors reduced

Commonly confused with

Common wine styles

Common grape varieties

Common regions

Related winemaking techniques

Serving implications

Beginner explanation

A Chardonnay that smells like movie-theater butter — without fruit — likely has diacetyl excess, not balanced MLF.

FAQ

Is buttery Chardonnay always a fault?
No — intentional MLF produces moderate buttery notes. The fault is when diacetyl dominates and masks fruit.
Will diacetyl fade in bottle?
It can diminish slowly as diacetyl converts to less aromatic compounds, but severe excess may never integrate.

Related ontology entities

See also

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