Copper poses notable challenges in winemaking due to its catalytic properties in oxidation and reduction reactions, which can impact wine quality significantly. Particularly sensitive are grape varieties like Sauvignon Blanc and Cabernet Sauvignon, where copper can alter their distinct aromas rich in thiols.
Sources of Copper in Grape Juice
Copper found in grape juice primarily originates from fungicides containing copper used in vineyards. The exact amount derived from soil versus fungicide use remains difficult to quantify accurately, making it crucial for winemakers to monitor and manage copper levels throughout grape processing.
What Constitutes High Copper Concentrations in Must or Juice?
The concentration of copper in grape juice typically remains below 0.5 mg/L in the absence of copper-based sprays. However, this can rise significantly based on the frequency and dosage of fungicide applications, potentially exceeding 15 mg/L closer to harvest. While levels around 10 mg/L may not directly inhibit fermentation, other factors like residual agrochemicals and high ethanol content can exacerbate potential issues.
Impact on Fermentation and Mitigation Strategies
Research indicates that copper concentrations between 10-15 mg/L can inhibit fermentation and alter wine color due to increased oxidation. During fermentation, most copper is removed through sulfide formation and binding to yeast lees. To mitigate potential issues, winemakers are advised to select robust yeast strains, monitor yeast assimilable nitrogen (YAN) levels, and ensure stable fermentation conditions.
Use of Copper During Fermentation
Copper sulfate is commonly used during fermentation to mitigate hydrogen sulfide (H2S) odors. However, its interaction with wine compounds can affect aroma intensity, particularly in varieties sensitive to thiol alteration. Careful consideration is necessary to balance its use effectively while preserving wine quality.
Adding Copper Before Bottling
Adding copper sulfate before bottling, especially with screw cap closures, is discouraged unless wines exhibit clear reductive qualities. This precaution helps avoid potential post-bottling issues such as haze formation and undesirable chemical reactions during aging.
In conclusion, while copper plays a pivotal role in managing certain winemaking challenges, its careful application and monitoring are crucial to uphold wine quality and preserve varietal characteristics. Awareness of its potential impacts on fermentation and aroma profile underscores the importance of informed decision-making throughout the winemaking process.