Wine Fault

Protein Haze

Physical

Protein haze is a visual fault where unstable grape proteins precipitate as a cloudy or milky suspension, often triggered by warm storage. The wine may taste unchanged but appears unappealing and suggests inadequate fining.

Also known as: Protein instability, Heat haze, White wine haze

Typical severity: Low

Cause

Heat-sensitive grape proteins aggregating when wine warms above typical cellar temperatures.

How it occurs

Insufficient bentonite or protein stabilization before bottling leaves proteins that coagulate in warm transit or retail storage. Some varieties are naturally higher in unstable protein.

Prevention

Bentonite fining, heat stability testing, and cold conditioning before bottling to precipitate proteins in tank rather than in bottle.

Descriptors created

Descriptors reduced

Commonly confused with

Common wine styles

Common grape varieties

Common regions

Related winemaking techniques

Serving implications

Beginner explanation

Cloudy white wine that tastes fine may be protein haze — harmless but a quality control failure, not intentional natural wine character.

FAQ

Is protein haze harmful to drink?
No — it is a visual stability fault. The proteins are natural grape material, not microbial spoilage.
Will chilling clear protein haze?
Chilling may reduce visible haze temporarily, but the underlying instability remains without proper fining.

Related ontology entities

See also

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