Does My Fermentation Have Too Much Sugar?

I have been making wine for years and never had any trouble, but I tried a new wine recipe and made a six gallon batch. I’m afraid the specific gravity of the must was too high-1.1200 + and it has stalled out at about 1.100–too sweet. We will not drink wine that sweet. Is there any way I can salvage the 6 gallons by blending or trying to restart fermentation?
Name: John S.
State: Kansas
Hello John,
Your starting Specific Gravity on your wine hydrometer is a little high. We normally don’t recommend starting a fermentation any higher than 1.100. At an S.G. of 1.120 the potential alcohol for the fermentation is right at 15%. That’s just a little too high to shoot for and not have a potential for a stuck fermentation. The higher sugar concentration starts to act as a preservative, inhibiting the wine yeast activity.
Having said this, there is something that is a little puzzling. You say that the fermentation started and moved 20 points down to a Specific Gravity of 1.100. If the sugar level of the wine must was the issue at hand, typically the fermentation would not start at all. The fact that it did start tells me that the sugar concentration of the must is not  what’s causing the stuck fermentation. Or at least, it is not the main contributing factor.
Now the obvious question is: If it’s not the sugar level that’s holding the fermentation up, what is?
This could be one of an array of issues. It could also be a combination of two or more issues. While there may be something else causing the stuck fermentation, the higher sugar concentration level could be a contributing factor. It could be the jab to the upper-cut.
We could go through all the reasons why here, but that would not be very productive, and it would require me to go through a back-and-forth of questions and answers with you to get to the bottom of things. But here’s what we can do. On our website, we have put together The Top 10 Reasons For Fermentation Failure. This is a list of what we have discovered to be the top reasons why a wine must is not fermenting.
This list has been compiled through many years of experience with helping home winemakers through their more challenging moments. It is my feeling that this list covers well over 95% of the issues we run across. By going through them I’m fairly confident that we can solve your stuck fermentation riddle.
Going back to your sugar concentration, I wanted to bring up something real quick. I don’ t believe it to be the primary problem, currently, but as the fermentation continues and the alcohol level rises, it could indirectly cause a problem with the fermentation being able to finish completely. Just as too much sugar can interfere with a fermentation, so to can too much alcohol.
Happy Winemaking,
Ed Kraus
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Ed Kraus is a 3rd generation home brewer/winemaker and has been an owner of E. C. Kraus since 1999. He has been helping individuals make better wine and beer for over 25 years.