True mold rarely appears on wine. If you see mold on the cork, you only need to decant the wine into a sterilized bottle and seal it using a non-cork stopper. Yeast spores, which appear as paper-like dot on the surface of wine, are common. Other wine maladies -- mycoderma, ropiness and a musty aroma -- have a mold-like appearance and are usually correctable.
To check if the substance is mold or a yeast-based growth or imperfection, take a sample using a wine thief, a pipette used to obtain a sample for testing. Rub the suspected mold between your thumb and forefinger; mold rolls up into a rubbery cylinder, whereas yeast smears. If the substance proves to be mold, take another sample and place it a sterilized food-grade container. Take the mold to the retailer who sold you the kit with its serial number and receipt. This type of mold is a rare thermophilic form that kit makers track and record.
Mycoderma, the 'Flowers of Wine'
Also known as flowers of wine, mycoderma results from oxygenation, insufficient sulfite and low alcohol content. If you smell an aggressive vinegar odor and mycoderma has covered the entire surface of the wine, you must toss it out, as painful as that is. If you smell just a hint of vinegar, top up the carboy, a large fermentation container, with a similar bottled wine to prevent additional growth. If you see partial growth on the wine surface, filter the wine into a sterilized carboy and add enough sulfur solution to bring it to between 30 and 50 ppm. Bottle the wine as soon as possible.
Drawing the Line on Ropiness
Ropy wines have a thick layer of oily, mucilaginous growth with thread-like strands on their surface caused by leuconostoc, a gram-positive yeast bacteria. Pour the affected wine into a large container; you need a few inches of space in the container above the surface of the wine. Beat the wine with a whisk or hand mixer until frothy and mix in two crushed sodium metabisulfite tablets per gallon. Cover the container with cheesecloth and secure it with twine. Stir the wine every hour for four or five hours and transfer it to a sterilized fermentation container. Let the wine sit for a couple of days and filter it into another sterilized fermentation container to finish.
Moldy Taste and Smell
Wine doesn't have to look moldy to taste and smell that way. Moldy and musty tastes for when you wait too long to siphon off the sediment, or lees. This type of moldiness has an easy fix. Add a crushed sodium metabisulfate tablet and 1/2 ounce of activated charcoal to the wine and stir. Stir the wine every four to six hours for 24 hours then let the wine sit for 24 hours. Filter the wine through several layers of cheesecloth or muslin and into a sterilized carboy.