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Stuck Fermentations

TroubleShooting

Drew France — Middletown, Connecticut asks,
Q

I have a 59-gallon (223-L) batch of a 50% Cabernet Sauvignon, 50% old vine Zinfandel blend that is in oak. I pressed it in the fall with my stepdad. I used his family recipe, utilizing wild yeast from grapes to ferment it. Everything looks, smells, and tastes great with a delightful fruity nose, but it is only testing at 9% alcohol. His batch (same process) is at 15% alcohol. The only difference in the two wines is that mine was racked from glass to oak and placed in my cellar after two months. Fermentation seemed to slow a few days after. He wants me to add 100 proof vodka to stabilize it, but I would rather not turn it into a Port style. Will simply raising the temperature of wine restart fermentation, or do I need to pitch yeast? I really don’t want to lose all this beautiful wine. Please help.

A
Before you start going crazy with a fermentation restart protocol, are you sure that it is really stuck? The first thing that I would advise you to do is to taste and compare your wine with your stepdad’s. At 9%, and compared to 15%, you should notice sweetness on the palate. If your wine tastes dry or similar to his, then it might be a measurement or instrumentation problem. I’d also suggest sending a sample to your nearest wine lab (I use ETS Labs based in St. Helena, California, and there are many others around the country) and get an alcohol measurement to make sure your 9% is a “real” number as well as to see what the residual sugar is, i.e. how far you’ll have to go if you do need to do a re-start. Unfortunately, human error and equipment variation can sometimes give us the wrong numbers. Restarting a stuck fermentation is very difficult at this stage and takes a lot of time and some expense (more yeast, more nutrients, etc.) and somehow never quite makes the wine
Response by Alison Crowe.