Mycoderma aka Flowers of Wine
Mycoderma, known as Flowers of Wine, is a spoilage yeast like organism which forms a film on the surface of the wine exposed to air. It starts as small islets then coalaces to cover the surface of the wine. When disturbed , the islets bead up and drift down through the wine like snowflakes. Mycoderma oxidizes the alcohol to Co2 and water forming a by-product that includes acetic acid.
Mycoderma is aerobic meaning that oxygen is required for growth and development of the flowers or film on the surface of the wine. You can prevent its appearance by excluding air from your wine during secondary fermentation and aging. A common cause of this spoilage is poor seal from bungs. Screw caps are another culprit. Also, fermentation locks should be properly filled with sulphite solution and containers should be topped up.
At too high pH or too low acidity, So2 is much less effective. Therefore, such wines are much more prone to oxidation, acetic spoilage and mycoderma. Maintaining a So2 level of 30-50 ppm at all times is one of the best preventatives.
Once the mycoderma has completely covered the surface of the wine the resulting bad flavors cannot be removed or disguised. The only option is to throw it out.
If you detect mycoderma early enough by noticing the first few small islets and a trace of sour, vinegary smell, eliminate their access to air by filling up that space and keeping it filled, thus asphyxiating the spoilage micro-organism.
Didn't catch it in time? These suggestions may enable you to eliminate the bad flavor and save the wine:
1. Sterile filter.
2. Add 50-100 ppm of sulphite, that's 1-2 Campden Tablets per gallon.
3. Bottle immediately.
4. Thoroughly disinfect the fermentor in which the mycoderma appeared and anything else in which it came in contact.