Dealing With a White Film on Fermenting Wine: How to Handle Bacterial or Yeast Contamination

When you notice a white film on your fermenting wine, it's important to determine its origin and take appropriate measures to ensure the quality and safety of your wine. This guide will help you identify the possible causes and provide solutions to address the issue.

Understanding the White Film

In your experience, if the white film is papery, it is likely a microbial contamination, specifically bacterial. While it is not considered poisonous, such contamination can affect the aging process of the wine, making it less favorable over time. If you have this issue, it's best to rack the wine, leaving the top layer of the film behind, and bottle it as soon as possible.

For those who are scientifically inclined, holding one bottle for a year or two can provide insight into the condition of the wine. If you notice any changes, it is recommended to take necessary steps to address the contamination.

Assessing Fermenting Wine After the Initial Fermentation

Depending on what you mean by "fermenting wine," the white film could arise from different stages. During the active fermentation period, you will see numerous bubbles and items rising to the surface. If the white film occurs after the fermentation has stopped or during the malolactic phase, you need to consider different factors.

Floret Yeasts: A Common Cause of White Film

A common cause of the white film is floret yeasts, particularly if you use minimal sulfur in your wine. These yeasts appear when the sulfur levels in your wine are insufficient. Skimming them off once fermentation and malolactic conversion are completed is sufficient. For red wines, increasing the sulfur to 30-40 ppm can resolve the issue.

However, if you are dealing with rosé or white wines, there is a chance that after 12 months, the wine may develop sherry-like flavors. While not necessarily unpleasant, these flavors might not be desirable, depending on your preferences.

Other Possible Causes

In cases where you are making wine in unsanitary conditions, the white film might be due to a slime mold. Adding more sulfur is a good solution to address this issue.

Additional Tips and Recommendations

Skim the Film: Always skim off any visible film to prevent further contamination. Avoid Sensory Changes: Be aware that certain solutions, like adding sulfur, might lead to sensory changes in the wine over time. Regularly monitor the wine's condition. Sanitize Equipment: Ensure all equipment is thoroughly sanitized to prevent bacterial or yeast contamination.

Conclusion

Identifying and addressing the white film on fermenting wine is crucial for maintaining the quality and safety of your product. Whether caused by bacteria, yeast, or other factors, taking appropriate measures can help mitigate the issue and ensure optimal results.