Photo is of an infected wine shortly after separation from solids. Fermentation in the must seemed normal, but stopped once in carboys as this white slime appeared. I have worked this vineyard for several years with conventional spray, fertilizers, beetle traps and grooming without ever having this problem. Grapes were well washed before crushing, but not presoaked in a camden solution.
What is this stuff? Can I save this batch and get fermentation restarted, and would it then be safe to drink, and how can I prevent this in the future? Thanks, Lee
Mostly likely you have one of 2 things going on. Either it is a film yeast formation, which causes your wine to oxidize to a Sherry form or it is acetic acid bacteria, which causes the wine to turn to vinegar.
The reason this happens is due to oxygen exposure. Notice the film is occurring at the interface of the wine and atmosphere (oxygen), so the microorganisms that form there likely require oxygen to survive. It is safe to drink, but it may not taste very good (may be better for cooking).
Any time you have headspace/oxygen exposure, you run the risk of microbial contamination and spoilage.
You can attempt to skim this film off the top of your bucket. I would probably rack this into a carboy if you want to save it. Make sure you pre-sanitize the carboy using a citric acid-SO2 solution prior to putting the wine in there. And fill the carboy so that you have limited headspace. If you don't have enough wine to fill and cap a carboy you can sanitize marbles and then add them to the carboy to push the volume of wine up and reduce headspace. Also make sure to make some SO2 additions (which should be made according to the wine's pH to be effective as an antimicrobial). There is a fact sheet about SO2 and its relationship in wine that may be helpful: http://pubs.cas.psu.edu/FreePubs/PDFs/ee0093.pdf
For the future, I would highly recommend sanitizing the parts of your bucket that do not have wine touching them with 40-70% food grade ethanol. Having bits of juice/wine/debris on the interior part of your vat or storage vessel leaves you at risk for microbial contamination.
Thank you, Denise, for your thoughtful answer. Attempting to keep my wine as "pure" as possible, I try to avoid using any chemical additives if at all possible, and have been making wine successfully this way for many years, but apparently my good luck has finally run out. This wine is in low head, air locked carboys. Some was put in the open bucket for clear photo purposes only. I agree that I will have to be more aggressive about sanitation in the future, but for now I would like to know if I can get fermentation restarted. When this slime first appeared I did treat the filled carboys with SO2 and reyeasting twice to no effect. Right now I'm letting the batch suffer at 30 degrees in the hope that this slime will "freeze" after which I will reyeast it yet again. So far it does not taste like vinegar. Any other suggestions you may have will also be greatly appreciated, and thanks again, Lee
You may be able to get the re-fermentation started if the pH/SO2 combination isn't inhibitive. (Fermentation yeast are generally more sensitive to SO2 than surface yeasts.) Of course, the strength of the SO2 is completely dependent on the pH of the wine, which I believe is covered slightly in the previous attachment I sent you.
Is there any residual sugar (i.e. sweetness) left in the wine? If there isn't, it may be challenging to re-start the fermentation. However, you could follow a re-fermentation protocol by separating out a portion of your finished wine, and add sucrose (table sugar) to that portion of your wine. Add wine yeast, get the fermentation to start, and slowly acclimate to your wine again. It is similar to re-starting a stuck fermentation: http://www.enartisvinquiry.com/download/protocols/Restart%20Stuck%20Fermentation.pdf
You can use whichever yeast you have, but a stronger yeast will definitely be more helpful because it's dealing with challenging wine conditions. Best, Denise