Protein haze

Protein haze meaning in wine

Protein haze is a clarity defect in wine characterized by a cloudy, turbid appearance caused by an excessive concentration of protein particles that react with tannins and other phenolic compounds. This condition typically develops when proteins naturally present in grape juice—primarily from the grape pulp and skin contact during fermentation—remain in high concentrations in the finished wine. The proteins can precipitate and form visible particles, particularly when exposed to temperature fluctuations, pH changes, or during aging. White wines are more susceptible to protein haze than reds, as red wines naturally lose most proteins during fermentation due to their interaction with tannins. The haze becomes more pronounced when wines are chilled, making it especially problematic for wines intended for cold service. Winemakers routinely test for protein stability using heat tests that simulate potential haze formation. Treatment involves fining with bentonite clay, a negatively charged agent that attracts and binds to positively charged proteins, allowing them to settle and be removed through filtration or racking. Other protein-removing fining agents include isinglass and egg whites, though bentonite remains the most common commercial solution for preventing this aesthetic flaw.